# Kohler vs Generac standby



## Speedy Petey (Feb 1, 2004)

Generac is OK. Well made, decent warranty. Easy to install. Transfer switches are well laid out. 

Kohler is very well made, better warranty. Not bad to install. New ones require special shielded cable for the controls (ie: NOT found in home centers). 
The one thing I do not like about the new Kohlers is the plastic housing. It cracks WAY too easily. PLEASE don't ask me how I know this. 

What is the running amps of the A/C?


----------



## 7474 (Dec 8, 2008)

Speedy Petey said:


> Generac is OK. Well made, decent warranty. Easy to install. Transfer switches are well laid out.
> 
> Kohler is very well made, better warranty. Not bad to install. New ones require special shielded cable for the controls (ie: NOT found in home centers).
> The one thing I do not like about the new Kohlers is the plastic housing. It cracks WAY too easily. PLEASE don't ask me how I know this.
> ...


Thanks for the reply.
The rated load amps for the compressor is 19.2 with a power factor of .94. The full load amps for the condenser is 1.7. Not that I know what any of that means, but it was the info on the Lennox engineering data book for the unit.
Thanks again.


----------



## Yoyizit (Jul 11, 2008)

Same question for a gen to run only a central AC unit: 4500W continuous and 4x this much during startup.

I'm waiting on two generator companies to also answer this question so now I guess I'll try to e-mail Kohler.


----------



## wkearney99 (Apr 8, 2009)

FWIW, I have a Generac and my neighbor has a Kohler, both of the same capacity. The Generac is noticeably quieter. Something to think about, both for the noise in your own house during the outage, and that of your neighbors stuck with their windows open trying to cool off in this summer heat.


----------



## Auger01 (Sep 13, 2011)

You might also consider Onan. Costco probalby has the best prices for the Onan generators. If must go with generac, I would go with the Quietsource series. They have automotive style engines and aluminium enclosures. 

The best way to figure your AC starting current is to put a clamp meter on the unit and start it up. They can capture the starting current required.

A "Hard Start Kit" will also reduce the amount of power that your ac needs to start. The kit has a Capacitor that helps to start the AC thus reducing the power needed to start it. 

Here is the kit I put on my AC:

http://five-two-one.com/

They cost about 45 bucks on ebay. It reduced the starting current of my four ton ac from about 90 to 42 amps. That allows me to run the ac on my 12kw generator without problem.


----------



## Missouri Bound (Apr 9, 2011)

My Generac sounds like a small lawn tractor. I don't consider AC a necessity in the event of a power failure, so I chose an 8KW unit. It's been 3 years with no issues. LIghts, tv, home office, fans and keeping the freezer and refrigerators operating. Generac has improved greatly in the last few years, Kohler has always been good. A 10k generator is capable of delivering 41A @ 240v. Watts divided by voltage equals amperage.:yes:


----------



## stickboy1375 (Apr 28, 2012)

7474 said:


> Looking for opinions on Kohler vs Generac for standby home generators.
> 
> Also, have a 4 ton Lennox 13ACD Merit series with compressor locked rotor amps of 97 and condenser locked rotor amps of 3.1. What size generator would be needed to start this unit?
> 
> Thanks for any assistance.


Just as a heads up, if you choose not to include the AC in your generator needs, with a automatic generator, you will have to provide load shedding to disable the AC. Generac provides this feature in its newer ATS. (automatic transfer switch)


----------



## Speedy Petey (Feb 1, 2004)

stickboy1375 said:


> Just as a heads up, if you choose not to include the AC in your generator needs, with a automatic generator, *you will have to provide load shedding to disable the AC*. Generac provides this feature in its newer ATS. (automatic transfer switch)


Not if it is sized properly. :whistling2:


----------



## stickboy1375 (Apr 28, 2012)

Speedy Petey said:


> Not if it is sized properly. :whistling2:


Yeah, I think I indirectly mentioned that.  That was my point, I just didn't come out and say it.


----------



## Speedy Petey (Feb 1, 2004)

stickboy1375 said:


> Yeah, I think I indirectly mentioned that.  That was my point, I just didn't come out and say it.


Then I think I misunderstood your comment. :001_unsure:


----------



## stickboy1375 (Apr 28, 2012)

Speedy Petey said:


> Then I think I misunderstood your comment. :001_unsure:


Not your fault, I totally missed my mark.


----------



## 7474 (Dec 8, 2008)

Auger01 said:


> You might also consider Onan. Costco probalby has the best prices for the Onan generators. If must go with generac, I would go with the Quietsource series. They have automotive style engines and aluminium enclosures.
> 
> The best way to figure your AC starting current is to put a clamp meter on the unit and start it up. They can capture the starting current required.
> 
> ...


Thanks.
I was thinking the same thing regarding the hard start kit. I presented this on an HVAC site looking for a quantification of the reduction and one of their moderators stated the amp draw for start up would be the same with the hard start kit but would be for a shorter time. Didn't really understand this as my understanding of the hard start kit was as you had stated.


----------



## 7474 (Dec 8, 2008)

Speedy Petey said:


> Not if it is sized properly. :whistling2:


With a home full of gas appliances (stove, dryer, hot water, furnace) and CFLs, how would you size the generator based on the AC. Kohler's site says the 14res can easily start a 5-ton AC. However, the generator rep out to my house stated I would need at least a 17 or 20 kW unit.


----------



## Auger01 (Sep 13, 2011)

7474 said:


> Thanks.
> I was thinking the same thing regarding the hard start kit. I presented this on an HVAC site looking for a quantification of the reduction and one of their moderators stated the amp draw for start up would be the same with the hard start kit but would be for a shorter time. Didn't really understand this as my understanding of the hard start kit was as you had stated.


All I can say about that is that the Fluke (meter) doesnt lie. :yes:


----------



## Auger01 (Sep 13, 2011)

7474 said:


> With a home full of gas appliances (stove, dryer, hot water, furnace) and CFLs, how would you size the generator based on the AC. Kohler's site says the 14res can easily start a 5-ton AC. However, the generator rep out to my house stated I would need at least a 17 or 20 kW unit.


Not all 5 ton ac's are the same. Factors such as compressor type and age of the unit have a bearing on starting current. While the 14kw unit may start the ac with no other loads, if you are running things such as the microwave, refrigerator and lets say a hair dryer, there may or may not be enough excess capacity in the 14kw unit to start the ac. 

Did the rep do a load calcuation at your house or did he just automatically reccomend the 17-20kw units?


----------



## stickboy1375 (Apr 28, 2012)

Auger01 said:


> Not all 5 ton ac's are the same. Factors such as compressor type and age of the unit have a bearing on starting current. While the 14kw unit may start the ac with no other loads, if you are running things such as the microwave, refrigerator and lets say a hair dryer, there may or may not be enough excess capacity in the 14kw unit to start the ac.
> 
> *Did the rep do a load calcuation at your house or did he just automatically reccomend the 17-20kw units?*



Im betting the farm I know how he decided this factor.


----------



## Yoyizit (Jul 11, 2008)

Auger01 said:


> A "Hard Start Kit" will also reduce the amount of power that your ac needs to start. The kit has a Capacitor that helps to start the AC thus reducing the power needed to start it.


Yes. 
The highest surge vs. rated watts ratio for a Grainger listed generator that I could find was 1.6 and many motors have a much higher ratio.

BTW, I don't guess PoCo ever has to worry about this ratio for their generators.


----------



## 7474 (Dec 8, 2008)

Auger01 said:


> Not all 5 ton ac's are the same. Factors such as compressor type and age of the unit have a bearing on starting current. While the 14kw unit may start the ac with no other loads, if you are running things such as the microwave, refrigerator and lets say a hair dryer, there may or may not be enough excess capacity in the 14kw unit to start the ac.
> 
> Did the rep do a load calcuation at your house or did he just automatically reccomend the 17-20kw units?


He made his recommendation based on the LRA of the AC, 97 amps. He then looked at the electrical panel and said "you have no load on this house except the AC".


----------



## 7474 (Dec 8, 2008)

Yoyizit said:


> Yes.
> The highest surge vs. rated watts ratio for a Grainger listed generator that I could find was 1.6 and many motors have a much higher ratio.
> 
> BTW, I don't guess PoCo ever has to worry about this ratio for their generators.


From what I have read, all the generacs are 150% at 30% voltage drop. The Kohler's with the PowerBoost feature are 185%.


----------



## 7474 (Dec 8, 2008)

stickboy1375 said:


> Im betting the farm I know how he decided this factor.


He based the 17-20 on the LRA of the AC which was 97 amps. He also looked at the electrical panel and stated "you have no load on the house except the AC". He was the first rep out, more to come.

My simple understanding of electrical need is 97A x 240V = 23,280 watts to start the AC?


----------



## Yoyizit (Jul 11, 2008)

Another thing from Grainger is that the price per watt goes from $0.20 to $2.00 which is an order of magnitude. This seems to be an inordinately wide range.

And one contractor quoted me about $0.80/w for an installed, large, resi unit.

Is this variation due to supply and demand? Quality?


----------



## 7474 (Dec 8, 2008)

Auger01 said:


> You might also consider Onan. Costco probalby has the best prices for the Onan generators. If must go with generac, I would go with the Quietsource series. They have automotive style engines and aluminium enclosures.
> 
> The best way to figure your AC starting current is to put a clamp meter on the unit and start it up. They can capture the starting current required.
> 
> ...


Further review on the HVAC site regarding hard start kits showed they may drop the amp draw with an amp meter but this is too slow of a measuring device. When measured with an oscilloscope the amp draw of the AC with a hard start kit is still the same as without.

However, you and many other have shown with their amp meters and real world experience the AC running on much smaller generators. 

My electrical understanding is minimal at best, but I think originally for yourself 90A x 240V = 21,600 to start your AC. Mine would be even higher with 97 amps. Based on this we would both need the 20kW at least, but you are getting by on much less.


----------



## stickboy1375 (Apr 28, 2012)

7474 said:


> He based the 17-20 on the LRA of the AC which was 97 amps. He also looked at the electrical panel and stated "you have no load on the house except the AC". He was the first rep out, more to come.
> 
> My simple understanding of electrical need is 97A x 240V = 23,280 watts to start the AC?


Odd, I've never done a load calculation by 'looking' at an existing panel. Lol...


----------



## 7474 (Dec 8, 2008)

stickboy1375 said:


> Odd, I've never done a load calculation by 'looking' at an existing panel. Lol...



I appreciate your time with replying but you have yet to offer any insight only your pleasant sarcasm. 

I provided you with my understand of the electrical requirements of the AC alone, 97A x 240V = 23,280, which on NG would be a 20kW at least. Is this correct? 

The other electrical appliances in my home all running at once would be about 6 kW.


----------



## 7474 (Dec 8, 2008)

Auger01 said:


> You might also consider Onan. Costco probalby has the best prices for the Onan generators. If must go with generac, I would go with the Quietsource series. They have automotive style engines and aluminium enclosures.
> 
> The best way to figure your AC starting current is to put a clamp meter on the unit and start it up. They can capture the starting current required.
> 
> ...


I see there are (2) 4 ton options, the 3-5 ton and 4-5 ton. Which did you choose for your unit and why? Based on your price, I would believe it was the 4-5 one.


----------



## Auger01 (Sep 13, 2011)

7474 said:


> I see there are (2) 4 ton options, the 3-5 ton and 4-5 ton. Which did you choose for your unit and why? Based on your price, I would believe it was the 4-5 one.


I have the 4-5 ton one. I got that model because the capacitor is bigger and provides more "kick". You dont want to oversize the start capacitor too much however, because that can cause other problems.

Also consider that LRA or "locked rotor amps" is the current draw with the compressor not moving or stalled. While that has a loose correlation to the starting current required, it is NOT the same because obviously the compressor is moving when it is started. 

Its probably true that the current required is the same with or without the hard start kit. However, if my fluke cant detect the current on peak hold mode, neither can the generator. :icon_cool:


----------



## Auger01 (Sep 13, 2011)

7474 said:


> From what I have read, all the generacs are 150% at 30% voltage drop. The Kohler's with the PowerBoost feature are 185%.


 
I would take all "surge" ratings from any manufacturer with a very, very large grain of salt. :whistling2: Most are very optimistic. A 30% voltage drop WILL cause a noticeable flicker in any lights that you have and also wont be very good for any sensitive electronic that you may have.


----------



## Yoyizit (Jul 11, 2008)

7474 said:


> When measured with an oscilloscope the amp draw of the AC with a hard start kit is still the same as without.


Then the kit must reduce the time it takes for the heavy current transient to die out, or somehow reduce the RMS current value, so that the total energy consumed by the transient is reduced.
It also depends on the transient response of the generator, and generic info on this is probably on the Web. 
PoCo's transient response is probably less than 20 mS and they can deliver 24 to 48 kw or more to a house.

It seems like with 3 kw you get some inconvenience and with 20 kW you almost get life as usual, and you'll use your gen a few days every two or three years.

And a small fan takes 50w, a fridge 500w and a central AC 5000w. 

This last time we used a table top single burner butane stove to do the cooking. Minimal initial investment and you only buy cartridges as you need them.

BTW, a 30% drop in voltage for incandescents will cause a 70% drop in brightness, in principle.


----------



## 7474 (Dec 8, 2008)

Yoyizit said:


> Then the kit must reduce the time it takes for the heavy current transient to die out, or somehow reduce the RMS current value, so that the total energy consumed by the transient is reduced.
> It also depends on the transient response of the generator, and generic info on this is probably on the Web.
> PoCo's transient response is probably less than 20 mS and they can deliver 24 to 48 kw or more to a house.
> 
> ...


Not sure how the kit works, as the HVAC experts say it decreases the time for start-up not the amp draw. But, I have seen numerous places, this thread included, where people are powering large ACs with relatively small gens because of the decreased amps noted with amp meter.

We could get by with very little and will probably rarely, if ever use it, especially with almost all underground utilities throughout our city. But, wife wants to make sure we have the AC available as family in Columbus, OH were without power for 4 days and especially since we have 3 under 3 y.o.


----------



## Yoyizit (Jul 11, 2008)

One company responds -

". . .a unit of at least 20kw depending on fuel type should be sufficient to start and run [my] unit."

He didn't mention hard start kits but it is not in his financial interest to do so, either.

One thing that makes this gen. question tricky as decision problem is that the HO's incentive to buy a generator increases as the time without power goes by.


----------



## wkearney99 (Apr 8, 2009)

Yoyizit said:


> One thing that makes this gen. question tricky as decision problem is that the HO's incentive to buy a generator increases as the time without power goes by.


Or frequency of outages. It's one thing to suffer 5 days straight (or 8 during Hurricane Isabel several years ago). But it's nearly as bad to have low voltage drop-outs and brief outages happening at least once a month, if not more during heavy weather incidents. This was also why I skipped going with a portable or even a manual transfer. The house already had a manual xfer panel and outside plug. The idea of hauling out the genset once a month was unacceptable. 

I wasn't pleased we had to shell out $10k, but we truly value the freedom from aggravation it's provided.


----------



## 7474 (Dec 8, 2008)

wkearney99 said:


> Or frequency of outages. It's one thing to suffer 5 days straight (or 8 during Hurricane Isabel several years ago). But it's nearly as bad to have low voltage drop-outs and brief outages happening at least once a month, if not more during heavy weather incidents. This was also why I skipped going with a portable or even a manual transfer. The house already had a manual xfer panel and outside plug. The idea of hauling out the genset once a month was unacceptable.
> 
> I wasn't pleased we had to shell out $10k, but we truly value the freedom from aggravation it's provided.


The inconvenience of a portable generator is also what steered us towards the whole house standby. 

What generator do you have? Problems? Things you would have done differently?

Thanks.


----------



## 7474 (Dec 8, 2008)

Yoyizit said:


> One company responds -
> 
> ". . .a unit of at least 20kw depending on fuel type should be sufficient to start and run [my] unit."
> 
> ...


I asked the one guy that was out about hard start kits. He said that if they were that beneficial they would be installed at the factory. He said he used to own a mech contracting company and they only put them on as a last ditch effort to save a compressor with very limited life left. 

From my reviews of HVAC forums, companies used to install hard start kits on every unit but in an effort to keep costs down to remain competitive they began to be removed from all except the higher level units.

Seems like a no lose situation with the addition of a hard start kit, especially the 5-2-1 Compressor saver at only $45.


----------



## wkearney99 (Apr 8, 2009)

7474 said:


> The inconvenience of a portable generator is also what steered us towards the whole house standby. What generator do you have? Problems? Things you would have done differently?


We bought Generac 20kw with an automatic transfer switch. Starts/stops itself automatically and tests itself once a week. I don't think we'd do much differently. 

Going whole house only cost us more up-front. The operational costs aren't appreciably different other than consuming more natural gas if you've got more stuff running. We really didn't have the room on the paneled wall for an interior transfer switch that would've worked with a smaller unit and only select circuits. We could've gotten by with a small unit and only selected circuits. But the cost increase on the units alone would then have to factor the added labor of rearranging the circuits in the breaker panel. 

Aim for as quiet as you can get. In the summer when everyone else has to leave their windows open it's nicer to have a quieter unit. Not for you, but for your neighbor's sake. If you're not close to anyone you'd still want to factor how much noise it'd make, for you inside the house.

I didn't go with their larger, cooled units as the capacity was more than we'll need and they're a LOT more expensive (nearly double). But they are quieter.

My advice is if you've got enough room near the electrical panel and want to save some money then a smaller unit is certainly worth considering. You really can live with only certain circuits being on the generator. It requires some forethought and possibly rearranging some circuits. It all depends on how your wiring is laid out and what your consumption patterns are like. 

Me, I wanted the HVAC to stay running, the hot tub to not freeze in the winter, and 2 refrigerators and 1 freezer to not spoil. Combine that with the lack of panel space, and it was worth spending the extra few grand to go with the 20kw whole house unit.

But I'd still absolutely go with an automatic unit and probably stick with the Generac brand. If only because I've heard how much louder the same sized Kohler is.


----------



## 7474 (Dec 8, 2008)

wkearney99 said:


> We bought Generac 20kw with an automatic transfer switch. Starts/stops itself automatically and tests itself once a week. I don't think we'd do much differently.
> 
> Going whole house only cost us more up-front. The operational costs aren't appreciably different other than consuming more natural gas if you've got more stuff running. We really didn't have the room on the paneled wall for an interior transfer switch that would've worked with a smaller unit and only select circuits. We could've gotten by with a small unit and only selected circuits. But the cost increase on the units alone would then have to factor the added labor of rearranging the circuits in the breaker panel.
> 
> ...


Thanks for the reply.

We are thinking 17 - 20kW with ATS from Generac. Originally was thinking the smaller panel with essential circuits as well to save money. But, after factoring in labor to move all the circuits figured for a couple hundred bucks more than the essential with extra labor we could have the whole house. 

I noticed how much more expensive the liquid cooled units are for the benefit of running at 1800 rpm vs 3600 for the air cooled. For the limited amount we will probably use it, don't see the RPMs making a whole lot of difference.

We also are mostly concerned about the AC. Without the AC we only have about 6-7kW with all our electric appliances running at once.

I have heard that the Kohler's are loud. Although, they do seem to be more fuel efficient at the 14kW level and to a lesser amount at the 20kW. Also, the warranty is better with the Kohler's. 5 years parts, 2 years labor for Kohler vs 3 years parts, 2 years labor for Generac.

Thanks again.


----------



## wkearney99 (Apr 8, 2009)

Sounds a lot like the decision making process I went through.

I turned every blessed thing in the house on, to it's highest power-consuming setting and we still only managed to push it to 85% load. With the AC already running, I didn't check the startup issue. But it's seriously unlikely we'd ever have the stove on broil-high, the microwave, AC, 2 fridges, 1 freezer, two hair dryers, all the computers (a 72" rack's worth), AV gear, TVs, the hot tub on high and heating, the vacuum and all lights lit, all at once. So yeah, we could probably use a 14kw and have no problems. We could pare back to just the 7kw and be really stingy with what was got used. For the added cost it was a no-brainer to go with the larger unit and avoid pretty much any complications.

We are in the process of renovating (by tearing the existing house down) and figured that into the equation also. So there's pretty much no scenario in which this unit wouldn't be suitable for us. 

As for warranties, eh, maintenance goes a long way. I'm following the vendor and dealer recommendations on service intervals. I'm sure, at some point, something expensive will crap out, but I doubt it'll be within the 1st 5 years. We're already into the 3rd and it's still running fine.


----------



## 7474 (Dec 8, 2008)

wkearney99 said:


> Sounds a lot like the decision making process I went through.
> 
> We are in the process of renovating (by tearing the existing house down) and figured that into the equation also. So there's pretty much no scenario in which this unit wouldn't be suitable for us.
> 
> As for warranties, eh, maintenance goes a long way. I'm following the vendor and dealer recommendations on service intervals. I'm sure, at some point, something expensive will crap out, but I doubt it'll be within the 1st 5 years. We're already into the 3rd and it's still running fine.


Those are also my thoughts regarding the 20, no scenario it can't handle. For about $200 more than the 17, why not. Although, if I could get away with the 14 from Kohler it would be about $800 less. But, might still want to go with the 20 just to cover any future additions.

Figure the maintenance goes a long way as with anything. Do you change your oil throughout the year with the changing of the temperatures, if you are in such a climate. We are in Northeast Ohio and looking at the owner's manual Generac requires different viscosities above and below 40 degrees (I believe).


----------



## wkearney99 (Apr 8, 2009)

I usually have it serviced any time it's been run for more than a few days straight, and then in spring/fall. I'm sure I'm probably wasting money doing it more often, but an oil change is a lot less expensive that bigger repairs. 

We have a boat so I'm used to the spring/fall servicing. I don't know if they used a different viscosity for winter. Here we haven't gotten really cold stretches lately.


----------



## Yoyizit (Jul 11, 2008)

My "utility function" must be different from you guys.

I'm now leaning toward a portable gen in the 5 to 6 kw range (liquid cooled for quietness if I can get it) that I can put in the back of my truck if necessary, and buying one more window AC to be put in the breakfast area or gathering place. We already have one for the bedroom.
Even if Pepco gets their act together these things are still useful.

If I got 20 kw, most of the time I'd be running substantially under capacity. 
But, since the avg. US house uses 4A continuously, 98% of the capacity of most houses is not usually used anyway.


----------



## 7474 (Dec 8, 2008)

Yoyizit said:


> My "utility function" must be different from you guys.
> 
> I'm now leaning toward a portable gen in the 5 to 6 kw range (liquid cooled for quietness if I can get it) that I can put in the back of my truck if necessary, and buying one more window AC to be put in the breakfast area or gathering place. We already have one for the bedroom.
> Even if Pepco gets their act together these things are still useful.
> ...


Unfortunately, nothing utilitarian about my set-up.

Wife's main reason is AC availability. We have (3) kids 3 and under.


----------



## 7474 (Dec 8, 2008)

Yoyizit said:


> One company responds -
> 
> ". . .a unit of at least 20kw depending on fuel type should be sufficient to start and run [my] unit."
> 
> ...


From an online generator sales company...."The 14kW (generac or kohler) will handle a 4 ton but depends on what else you want to run."

Will have to wait for the next couple sales reps to come out and give me a more detailed analysis.


----------



## bernie963 (Dec 18, 2010)

If you have not made a choice yet, check out the following site. Do a post and ask the question of generator experts.

www.smokstak.com and go to the generator forum also known as "sparks and arcs" 

havae a great day

bernie


----------



## 7474 (Dec 8, 2008)

bernie963 said:


> If you have not made a choice yet, check out the following site. Do a post and ask the question of generator experts.
> 
> www.smokstak.com and go to the generator forum also known as "sparks and arcs"
> 
> ...


Thanks, appreciate the info.


----------



## Yoyizit (Jul 11, 2008)

Two more companies have responded; one sent me to a dealer with a no-respond e-mail and the other had me go to an automated power calc. site which didn't work.

If you have trouble getting to an e-mail address on websites, go to "Press Releases". They usually have an employee address at the end of each article and so I just post my question and say "Please forward."


Let's say PoCo announced ahead of time that each year you would be without power for D consecutive days. Your choice is between a $500 gen and a $20K gen.
What value of D would be necessary for this decision to be a toss-up 
(see "indifference" below
http://www.transtutors.com/homework...and-decision/indifference-curve-approach.aspx)
for you?

For me it might be about 14 days or longer but for my wife it's 90 days. I thought it'd be the other way around but she's not the one who will be hooking up cords and lugging gas cans.

Historically PEPCO has lost power for a max of 5 days or so, so it's $500 for me for now.


----------



## 7474 (Dec 8, 2008)

Online generator sites say that the AC needs the 17 or 20 from generac.

Company 1 says Generac 17 at least, maybe 20.

Company 2 says Generac 14 will handle AC no problem.

From Generac ....."A 14kw would have 102 amps @ 240v with a voltage dip of 30%. A 17kw would have 125 amps @ 240v with a voltage dip of 30%.
Those numbers are for a unit running on LP. If you are using natural gas then those numbers can derate by up to 10%. I think based on these numbers and if the LRA is correct a 17kw would be a better fit for you. You could also look at the 20kw unit. It would have 145 amps @ 240v with a voltage dip of 30% on LP."

From hvac-talk.com, HVAC moderator answered that I would need 7.5kW to run the AC reliably while using other appliances.

Answers seem to be all over the board.


----------



## 7474 (Dec 8, 2008)

Further explanation from the HVAC site....

The LRA of 97 amps is what the compressor would draw for one hour running at the LRA. So, 97 x 240 = 23,280 watts or 23kW hour. Since the LRA only lasts about a second, 23,280 divided by 60 minutes divided by 60 seconds gives 6.5 watt seconds.


----------



## Auger01 (Sep 13, 2011)

7474 said:


> Further explanation from the HVAC site....
> 
> The LRA of 97 amps is what the compressor would draw for one hour running at the LRA. So, 97 x 240 = 23,280 watts or 23kW hour. Since the LRA only lasts about a second, 23,280 divided by 60 minutes divided by 60 seconds gives 6.5 watt seconds.


 
I think those HVAC guys are leading you down the primrose path. 
If you get a 7.5kw unit, odds are very high that are going to be very dissappointed if you expect it to run your ac. 

Amps is a measure of current. Watts is a measure of work. Volts times amps equals watts. Watts measured over time equals energy. 97 amps is what the unit would draw with a locked rotor or in other words a stalled condition. Breaking that down into killwatt hours or watt seconds does not help to define your problem. In other words, my my litte 200 watt inverter can also supply 23 kilowatt hours (kwh), it just takes it five days to do it. :whistling2: Assuming the circuit breaker didint trip any compressor drawing a LRA current for anything more than a few seconds would quickly be reduced to slag.


----------



## Auger01 (Sep 13, 2011)

Here is some good info from generac on sizing:

http://www.aapower.com/pdfs/SIZING GUIDE.pdf


----------



## jimmy21 (Jul 2, 2008)

Do you guys really have outages that often, and in the summer? Around here we only have maybe 2 or 3 outages a winter that last 15 minutes - 1 hour. I remember once in my entire life that it lasted something like 12 hours


----------



## 7474 (Dec 8, 2008)

Auger01 said:


> I think those HVAC guys are leading you down the primrose path.
> If you get a 7.5kw unit, odds are very high that are going to be very dissappointed if you expect it to run your ac.
> 
> Amps is a measure of current. Watts is a measure of work. Volts times amps equals watts. Watts measured over time equals energy. 97 amps is what the unit would draw with a locked rotor or in other words a stalled condition. Breaking that down into killwatt hours or watt seconds does not help to define your problem. In other words, my my litte 200 watt inverter can also supply 23 kilowatt hours (kwh), it just takes it five days to do it. :whistling2: Assuming the circuit breaker didint trip any compressor drawing a LRA current for anything more than a few seconds would quickly be reduced to slag.


The 7.5 was wishful thinking. I knew that it couldn't be that low of a generator. Just find it interesting that the "answers" to my needs are all over the place.


----------



## 7474 (Dec 8, 2008)

Auger01 said:


> Here is some good info from generac on sizing:
> 
> http://www.aapower.com/pdfs/SIZING GUIDE.pdf


Thanks...good find.

This follows in line with what Generac was saying in their reply. The 14 would provide 102 amps surge with LP, derated at 10% for NG, would only give me 92 amps. So, the 17 would be the better choice at 125 LP, 112 NG.


----------



## 7474 (Dec 8, 2008)

jimmy21 said:


> Do you guys really have outages that often, and in the summer? Around here we only have maybe 2 or 3 outages a winter that last 15 minutes - 1 hour. I remember once in my entire life that it lasted something like 12 hours


This is what it is coming down to now for us. 

We initially got interested in the generator secondary to my brother being without power for 5 days in Columbus, OH. Got us thinking. Was more spur of the moment/impulse buy. Just so happened the same day we found out about my brother, we had storms and knocked the power out for an hour. Having 3 kids 3 and younger also made us think about extended loss of power.

However, with some time to sit back and think. We have never had a power outage greater than an hour in 6 years. Total power outages probably number 5, if that, over 6 years. 

However, as with the market "past performance is not indicative of future results". But, we will probably forgo the back-up generator for now. Knock on wood.....


----------



## stickboy1375 (Apr 28, 2012)

jimmy21 said:


> Do you guys really have outages that often, and in the summer? Around here we only have maybe 2 or 3 outages a winter that last 15 minutes - 1 hour. I remember once in my entire life that it lasted something like 12 hours


Last October we had a freak snow/ice storm, was without power for a week.  I must have installed over 20 + generators that winter, all ranging from 12kw to 20 kw... thankfully it was an above average temperature for the winter.


----------



## jimmy21 (Jul 2, 2008)

7474 said:


> This is what it is coming down to now for us.
> 
> We initially got interested in the generator secondary to my brother being without power for 5 days in Columbus, OH. Got us thinking. Was more spur of the moment/impulse buy. Just so happened the same day we found out about my brother, we had storms and knocked the power out for an hour. Having 3 kids 3 and younger also made us think about extended loss of power.
> 
> ...



thats why i can't see spending the money on a whole house genset. Ive been debating buying a small portable generator, though. Just in case


Here is a question for people that do more of these. What would you do if you had customer that wants utility power, PV, a windmill, and a genset. I suppose they probably make special transfer switches for that.


----------



## wkearney99 (Apr 8, 2009)

Most residential PV or wind in populated areas is fed to the utility, not stored at the house itself. Dealing with battery maintenance is not trivial, so the idea is to use your roof to 'sell' the power into the local grid, not use it directly. Now, how that would get handled during a utility outage is an interesting question. Unless some sort of local storage was set up then it would likely go unused while the genset handled everything. For most residential situations that's reasonable. Making perfect use of it starts getting a lot more expensive.

Around here it's pretty much guaranteed you'll have an outage of greater than a day at least once a season, and regular low-voltage drops and short outages. Pepco is totally unreliable around here and that's not likely to change anytime soon.

At the very least it's worth considering a manual transfer panel and the ability to use a portable generator. A small portable unit to support the fridge and the HVAC blower will get you through an outage in the winter. Going for a little more capacity will power the AC system in the warmer months, if you want to run the AC at night and not hear the noise. Otherwise the small unit, run for a few hours each day, will keep the fridge cold enough to avoid spoilage. Assuming you have a manual transfer setup ready to accept it.


----------



## jimmy21 (Jul 2, 2008)

wkearney99 said:


> Most residential PV or wind in populated areas is fed to the utility, not stored at the house itself. Dealing with battery maintenance is not trivial, so the idea is to use your roof to 'sell' the power into the local grid, not use it directly. Now, how that would get handled during a utility outage is an interesting question. Unless some sort of local storage was set up then it would likely go unused while the genset handled everything. For most residential situations that's reasonable. Making perfect use of it starts getting a lot more expensive.


Oh thats true. Forgot about that. Most PV is fed to the power company. The inverter makes sure it has utility power, otherwise it shuts off.


----------



## 7474 (Dec 8, 2008)

jimmy21 said:


> thats why i can't see spending the money on a whole house genset. Ive been debating buying a small portable generator, though. Just in case


That was our thought process. Portable for just utilitarian aspects and maybe a window unit for extended outage. Then why not manual transfer switch so we don't have to deal with extension cords. Then, if were going to spend that much why not a little more for the whole house with AC. Finally, do we really need it since we have only lost power at most 5 times in 6 six years for a combined total of 90 minutes at most.


----------



## jimmy21 (Jul 2, 2008)

7474 said:


> That was our thought process. Portable for just utilitarian aspects and maybe a window unit for extended outage. Then why not manual transfer switch so we don't have to deal with extension cords. Then, if were going to spend that much why not a little more for the whole house with AC. Finally, do we really need it since we have only lost power at most 5 times in 6 six years for a combined total of 90 minutes at most.


I don't know about that. You could run most of the house on a 6kw portable generator. You could find a nice newer used one. For 600. Do some kind of manual transfer for a couple hundred. So youd be in it for around $1,000 and be fairly comfortable in an extended outage. Compare that to about 10k for a more ideal setup.
Sure, you wouldn't be able to run you heat pump, but you could still run a 110v heater or air conditioner. I can deal with that for 1/10 the cost


----------



## JayBird (Aug 23, 2007)

I'm a little late to game, but figured I'd add some info if you guys hadn't made a decision. I just had a Generac 20Kw stand by unit installed. Runs off LP. My A/C unit is about 13 years old, 3.5 ton, rated at 105 LRA. The Auto transfer switch handles all my circuits except washer/dryer and dishwasher. The set up was sold as a package deal from a local electric contractor. Adding a "whole house" transfer switch requires the meter to be pulled by the PoCo and you are at their mercy getting things back on line during the installation process. Price was more as well. I can live without washer/dryer and dishwasher during an outage.

Electric contractor installed a contact/relay for the hot water tank which when paired with Generac's Load shedding capabilities will shed the hot water tank if to much load is being called for. I was told my A/C has one already and the genny won't start it if I'm pulling to much load as well. I was also informed the 20kw unit has the ability to handle 140 LRA which I have not seen those specs from Generac, so I'm not sure where he got that info from.

Also generac states their 20Kw unit is rated at 18Kw with natural gas and a full 20Kw with LP. So keep that in mind depending on your fuel. 

Generac's units all have "load shedding" capabilities automatically and if you simply don't have the wattage available when calling for another big load item, it will shed something so you won't damage the unit. It really is a smooth system. You determine priority loads to shed. 

Everyone's needs are different. Some people aren't readily available to drag out their genny's during an outage. They may be working, have to work if your considered essential personnel during emergency related outages, away on vacation, etc. With an automatic system, you have piece of mind your fridges will be running and things will be carry on normally during an outage if your not home.


----------



## herdfan (Jul 7, 2012)

JayBird said:


> Generac's units all have "load shedding" capabilities automatically and if you simply don't have the wattage available when calling for another big load item, it will shed something so you won't damage the unit.


Not ALL. You have the transfer switch that does. I have the standard EZ-Switch which does not. I had to pick 16 circuits and that is all I get. But since I was DIY, I didn't want to complicate it any more that it already was.


----------



## JayBird (Aug 23, 2007)

herdfan said:


> Not ALL. You have the transfer switch that does. I have the standard EZ-Switch which does not. I had to pick 16 circuits and that is all I get. But since I was DIY, I didn't want to complicate it any more that it already was.


Yes, I kinda explained that wrong. I guess I meant to say is most of the generators have load shedding option when paired with the correct transfer switch.


----------

