# Reducing 15kw Heat Strip



## dac122 (Sep 5, 2008)

Yes, they make smaller heat strips. You'd have to research what sizes are available that fit in your air handler. 

But I'm not sure how that will lower your electric bill. A smaller heat strip may simply run longer.

If this is coupled with a Heat Pump perhaps you have the option to install primary, secondary and tertiary heat strips, depending on your heat pump and air handler. Or perhaps your system is not optimally configured.


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## tx_reeg (Sep 11, 2009)

I actually was trying to modify my 15kw heat strip to only run at 10kw's. I was assuming it would save money to only run the 10kw because it would be losing less power, and everywhere I have read 10kw would be more than enough to heat my size home. My air handler is 20 years old so I don't think I could find a heat strip that would fit.


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## mpoulton (Jul 23, 2009)

tx_reeg said:


> I actually was trying to modify my 15kw heat strip to only run at 10kw's. I was assuming it would save money to only run the 10kw because it would be losing less power, and everywhere I have read 10kw would be more than enough to heat my size home. My air handler is 20 years old so I don't think I could find a heat strip that would fit.


It will make no difference in your power bill. The heat strip does not "lose" 15kW in the sense of wasting it - it pushes 15kW of heat power into your home while it is on. When the temperature drops below a certain level, it turns on and runs until enough heat energy has been pushed into your home to raise the temperature enough to turn off the thermostat. How long it takes to push that much heat energy into the house depends on how much power the heat strip provides. A 15kW heat strip will run 1/3 less time than a 10kW. The total heat energy produced is the same, by definition, since that's what your thermostat actually responds to. It's also what you pay for on your electric bill.


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## tx_reeg (Sep 11, 2009)

mpoulton said:


> It will make no difference in your power bill. The heat strip does not "lose" 15kW in the sense of wasting it - it pushes 15kW of heat power into your home while it is on. When the temperature drops below a certain level, it turns on and runs until enough heat energy has been pushed into your home to raise the temperature enough to turn off the thermostat. How long it takes to push that much heat energy into the house depends on how much power the heat strip provides. A 15kW heat strip will run 1/3 less time than a 10kW. The total heat energy produced is the same, by definition, since that's what your thermostat actually responds to. It's also what you pay for on your electric bill.


Thanks for the info. I did not know that.


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## Yoyizit (Jul 11, 2008)

Supposedly you get the max efficiency by having the heater on all the time, so if you have a 10 kw or 11 kw or 12 kw or . . .heater running at 100% duty cycle on the 97.5% percentile day at your location then you are doing the best you can.
If you occasionally wear a sweater you might get by with less than 10 kw.
http://www.degreedays.net/
http://web2.airmail.net/danb1/climate.htm

Depending on how many heaters of what size you have, you can get several intermediate levels of power dissipation. 
Half the voltage = 1/4th the power, and since you'll be running these particular heaters at less than full power I can't imagine any safety concerns with this type of cross-strapping.

Or get a heat pump and divide your heating elec. bill by 3.
1 Therm of energy can be had from approx. 0.71 gal of fuel oil, 0.77 gal of gasoline, 100 cubic feet of natural gas, 1.1 gal of propane, 29 kwh of elec heat, 8.4 kwh of heat pump heat (COP = 3.5), 4.2 kwh of heat pump heat (COP = 6.9), 14 pounds of wood.
Or go solar. Texas must have high insolation.

3 tons = 10.5 kw[?]


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## beenthere (Oct 11, 2008)

You may be able to disable 5KW of that heat package.
If your air handler is in the attic. It may save you some money.
Since the hotter the air is in the duct work. The more heat the duct work loses in an unconditioned space.


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## newtech (Mar 21, 2009)

Yoyizit said:


> If you occasionally wear a sweater you might get by with less than 10 kw.
> [?]


Or.... how bout a snuggie:laughing: Does the same thing apply in the summer if you wear less you don't need as much cooling?


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## Yoyizit (Jul 11, 2008)

newtech said:


> Does the same thing apply in the summer if you wear less you don't need as much cooling?


Never tried it, but wearing wet clothes in moving air might work; kind of like your own personal evap. cooler. :thumbsup:

I knew of people in Austin who talked about sleeping under damp sheets back when almost nobody had A/C. She didn't mention fans but it would have worked much better. Maybe they didn't have elec., either. . .


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## zootjeff (Jul 11, 2007)

tx_reeg said:


> I actually was trying to modify my 15kw heat strip to only run at 10kw's. I was assuming it would save money to only run the 10kw because it would be losing less power, and everywhere I have read 10kw would be more than enough to heat my size home. My air handler is 20 years old so I don't think I could find a heat strip that would fit.



A heat strip is nothing but a big resistor, basically you need to make your heat strip have more resistance. If the construction is that of parallel coils of wire, removing a few of the coils could reduce it to less power. Since I don't know what kind of heat strip you have I can't tell you how possible this is.

Basically if you have 15kw and your running it at 240 volts, then your heatstrip is about 62 amps and 3.8. ohms. If you for instance were able to make the coil of wire longer, or remove some parallel portions of the element, you could increase the resistance and reduce the power. 10kW would be 41 amps and 5.8 ohms.

Something else to consider, if you wired two heat strips in series, you would double the resistance and reduce the power by half. You'd have 7.5kW heater using two 15kW heaters. If you wired them in parallel, you'd have 30kW...


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## beenthere (Oct 11, 2008)

Yoyizit said:


> Never tried it, but wearing wet clothes in moving air might work; kind of like your own personal evap. cooler. :thumbsup:
> 
> I knew of people in Austin who talked about sleeping under damp sheets back when almost nobody had A/C. She didn't mention fans but it would have worked much better. Maybe they didn't have elec., either. . .


It worked better without running a fan. A fan would cause the sheets to dry out faster. And then they would wake up sweating in the middle of the night.

Some people in AZ also used that same method.


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## beenthere (Oct 11, 2008)

Jeff. 

Your just making it sound more complicated then it is.


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## zootjeff (Jul 11, 2007)

beenthere said:


> Jeff.
> 
> Your just making it sound more complicated then it is.


I'm just explaining the theory. If you understand ohms law, it helps understanding the physics of what is going on with resistive heating. 
Power = Volts * Amps, Resistance = Volts / Amps.


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## beenthere (Oct 11, 2008)

Understanding ohm's law means nothing in this case. If you really don't know how strip heaters are configured.

And your post shows you don't know.


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## zootjeff (Jul 11, 2007)

beenthere said:


> Understanding ohm's law means nothing in this case. If you really don't know how strip heaters are configured.
> 
> And your post shows you don't know.



OK, you were right, I was wrong. You win. Now lets see some helpful guidance on re-config, rather then just insulting me.


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## yuri (Nov 29, 2008)

He can disconnect one of his 5kw strips if he can find which sequencer cuts in the last element. Otherwise the timing of the furnace will get screwed up. He may save a bit of heat due to less radiant heat loss in the ducts but not enough to notice a huge difference. If a house loses 10,000 BTU/hr it needs 10,000 replaced and it does not matter how quick that happens. On gas furnaces they are more efficient if running longer but not electric.


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## Yoyizit (Jul 11, 2008)

zootjeff said:


> OK, you were right, I was wrong. You win. Now lets see some helpful guidance on re-config, rather then just *insulting* me.


The first thing he did was "frame it and claim it".

Then, he [correctly or otherwise] interpreted your behavior back to you. 
It's called "Process Commentary" and is not cited much on the Internet in a useful way. 
Kids don't like to be at the receiving end of it and neither do adults. Politicians do it all the time.
As a countermove, I guess you could say, "I'm sorry you feel that way."
Or, I guess you could interpret his/her motives back to him/her, if you reasonably know what they are. This results in a 'tie'.
If your interpretation is correct, these people don't usually mess with you again.

Anyway, back to DIY business, if the OP knows the duty cycle of his existing setup he can guesstimate the lowest total strip power needed. I.e., 15 kw at 80% duty cycle needs 12 kw.


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## beenthere (Oct 11, 2008)

zootjeff said:


> OK, you were right, I was wrong. You win. Now lets see some helpful guidance on re-config, rather then just insulting me.


I gave him a possibility of what he may be able to do.

He hasn't posted anything back about about his brand to tell him anymore.

As long as people that don't know, don't confuse him. He will probably be ok.


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## beenthere (Oct 11, 2008)

Yoyizit said:


> Anyway, back to DIY business, if the OP knows the duty cycle of his existing setup he can guesstimate the lowest total strip power needed. I.e., 15 kw at 80% duty cycle needs 12 kw.


His best bet.

Is to spend a few bucks. And install an outdoor stat, to stage his heaters on.


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## Yoyizit (Jul 11, 2008)

beenthere said:


> His best bet.
> 
> Is to spend a few bucks. And install an outdoor stat, to stage his heaters on.


As an afterthought, I guess I did process commentary on you.

I doubt that knowing the theory can ever hurt anyone, and it may help. But DIY and contractor forums "do not suffer [theory] gladly*." 
Nerd/geek forums are way more tolerant of it.

Along those lines, apparently you and some others have given me a pass regarding theories, my own and theories in general.
Thanks. :thumbsup:

*II Corinthians 11:19


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## beenthere (Oct 11, 2008)

I believe I've told you more then once. You ain't even close.
And are doing more harm then good.

Powerpile thread comes to mind.

Just call them as i see them.

But, should probably wear my glasses more often then I do. :laughing:

If someone takes offense. Well, depends what they took offense to. 
Being wrong, or being pointed out that they are wrong. Or don't know what they are talking about.


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## tech2rescue (Jan 24, 2010)

Jeff, everything you said is 100% correct and the other gentleman must just be some cantankerous old coot with a deep-rooted psychological need to appear superior to others. I did exactly what you are talking about at my own house in MN. The system (that I got new for free) is actually oversized for the living space. I had an extra space or bay, whatever you call it, for a second heat strip in my unit, so I got one, installed it in that position, and wired the element (and thermal protection) in series with the other one. This cut the heat output by 1/2, just as you said. I did complicate it a little further by adding a couple of relays, that allow it to be switched back to one heat strip for quick warm-up on demand. I'm using a heat pump thermostat and using the AUX heat output to switch the unit to full output only when necessary, or when I set the thermostat to Emergency Heat. I had to spend a little money for the parts, but the system was free in the first place, and there is some satisfaction in having it behave exactly the way I want it to.


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## beenthere (Oct 11, 2008)

So did you wire a 5 KW heater in series to a 5 KW heater.
Or a 5KW heater in series with a 5 KW heater of a 10 KW heat package.
Or wire 5 KW in series with a full 10 KW heater.

If you wired it the way you said.
Then you could have installed a staged stage as easy, with out having to buy the extra heater, and relays.

Nothing wrong with building a Rube Goldberg in your own home.

Giving instructions for someone else to build in in their home?


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