# Outdoor combustion air?



## ttaylor (Feb 11, 2009)

I'm finishing a basement and building a small room with door around the gas furnace and gas water heater. Instead of putting an upper and lower opening/grill in the top and bottom of this new furnace room door I'd like to add an outside intake for fresh combustion air. I've been told I have to add two outside intakes, one high and one low but I know I've seen on those home reno shows a way of doing one intake pipe that comes in through the ceiling, climbs down the wall and then does a bend back up to 12" above the ground. The bend supposedly creates an air trap when the furnace isn't sucking air to prevent a lot of cold air from coming in. Anyone hear of this and anyone know how to size the pipe?


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## hvaclover (Oct 2, 2008)




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## yuri (Nov 29, 2008)

You can do it that way. Size depends on the amount of BTU's of your furnace and water heater (if you have one in that room) and your local gas code. In the old days we used 1 sq.ft /100,000 BTU's rule of thumb. A 6 " round pipe would be good for that amount. You need to make sure that the pipe does not have kinks in it if you are using insulated flex pipe. Call your gas supplier and they can look it up in their code book.


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## ttaylor (Feb 11, 2009)

Thanks. I read "if operating in a confined space, additional air may be added by a duct to the outside, sized on 1 square inch per 5,000 BTU input.". I'll take a look in the morning if I can find the BTU's of the furnance and of the water heater. 


I also read "To help keep incoming cold air in one place instead of allowing it to spread across your basement floor, build a closed-bottom containment box out of sheet metal or use a 5-gallon bucket that allows air to flow freely in and out. Drop the combustion air supply duct into the containment box and attach the duct permanently to it. To avoid restricting airflow, the box or bucket cannot be more than one foot high. "


I prefer the curve method I saw but have not been able to find anything about it on the net.


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## Revue (Jan 9, 2009)

ttaylor said:


> Thanks. I read "if operating in a confined space, additional air may be added by a duct to the outside, sized on 1 square inch per 5,000 BTU input.". I'll take a look in the morning if I can find the BTU's of the furnance and of the water heater.
> 
> I also read "To help keep incoming cold air in one place instead of allowing it to spread across your basement floor, build a closed-bottom containment box out of sheet metal or use a 5-gallon bucket that allows air to flow freely in and out. Drop the combustion air supply duct into the containment box and attach the duct permanently to it. To avoid restricting airflow, the box or bucket cannot be more than one foot high. "
> 
> I prefer the curve method I saw but have not been able to find anything about it on the net.


Google "saskatoon loop". Skuttle also makes a device.


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## hvaclover (Oct 2, 2008)

Can't say I ever saw one and won't believe til I see a professional paper on it.

Thermodynamics: Hot flows to cold until equilibrium is reached between two masses of equal volume.

The warm air in the "Trap" elbow that is supposed to prevent cold air infiltration on Heating off cycle would have more cold air in the pipe length then in the elbow. Hence, as I see it seems to me that there would be a chimney effect, a draft, in that pipe length as the smaller warm air volume migrates to the colder and higher cold air volume in the pipe .


Somebody correct me if I am wrong.


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## yuri (Nov 29, 2008)

Even with the trap cold air will migrate in as most houses have a chimney effect where air is rising up the stairs. The only solution is a Hoyme damper in the fresh air pipe and have it electrically interlocked to open when the furnace calls for heat. Cost $$ though.
http://www.hoyme.com/


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## hvaclover (Oct 2, 2008)

Skuttle make up air kit with counter balanced damper prevents cold air infiltration on off cycle.


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## ttaylor (Feb 11, 2009)

hvaclover said:


> Can't say I ever saw one and won't believe til I see a professional paper on it.
> 
> Thermodynamics: Hot flows to cold until equilibrium is reached between two masses of equal volume.
> 
> ...


If the warm air migrated then that would actually be a good thing! no? If the purpose of the Saskatchewan bend is to prevent cold air from continuing to flow into a room and along the floor then the warm air traveling out the pipe (if your correct and it migrates as opposed to just sitting in the bend) means no cold air is coming in. Unless your saying the warm air leaves and then the cold air comes in again. Hmmmm....

I've seen it done on some reno shows in cold climates like Saskatchewan.


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## yuri (Nov 29, 2008)

There is a lot of theory as to how this works. In real life as I am a tech and stand next to them I find that most of the time there is a draft flowing thru them. Most homes are under a negative pressure as hot air rises and leaks out thru chimneys etc. Adding the Hoyme damper allows air in only when the furnace is running. Still need some air for the water heater and you should NEVER seal that room up airtight. The Hoyme seems to eliminate the amount of draft. Have never seen the Skuttle unit but it must work like a barometeric damper and swing open by negative pressure. Every home is different so Internet advice while helpful is not 100% definitive/scientific.


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## hvaclover (Oct 2, 2008)

ttaylor said:


> If the warm air migrated then that would actually be a good thing! no? If the purpose of the Saskatchewan bend is to prevent cold air from continuing to flow into a room and along the floor then the warm air traveling out the pipe (if your correct and it migrates as opposed to just sitting in the bend) means no cold air is coming in. Unless your saying the warm air leaves and then the cold air comes in again. Hmmmm....
> 
> I've seen it done on some reno shows in cold climates like Saskatchewan.


I am saying it would suck air out of the enclosure. When the furnace fires it would draw air in.

But aiint no way a bend is going to stop the air from being sucked out by the chimney effect mentioned. End result enclosure evens out to the same cold air temp as the out side.

Might as well call that thing the "Newfie" bend for all it's good for.

Newfie joke courtesy of Wayne and Schuster.


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## hvaclover (Oct 2, 2008)

yuri said:


> There is a lot of theory as to how this works. In real life as I am a tech and stand next to them I find that most of the time there is a draft flowing thru them. Most homes are under a negative pressure as hot air rises and leaks out thru chimneys etc. Adding the Hoyme damper allows air in only when the furnace is running. Still need some air for the water heater and you should NEVER seal that room up airtight. The Hoyme seems to eliminate the amount of draft. Have never seen the Skuttle unit but it must work like a barometeric damper and swing open by negative pressure. Every home is different so Internet advice while helpful is not 100% definitive/scientific.



Skuttle works as you say. It runs from an outside hood air-intake to the cold air return. Furnace fires and blower starts. Blower suction opens a counter balanced normally closed damper allowing in fresh outside air.
Blower stops and counter balanced damper closes and stops
cold air infiltration .


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## yuri (Nov 29, 2008)

Do you have website/link for it? I would really like to see it. Hoyme's are expensive but good and I may sell these if I like them.

Thanks


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## Revue (Jan 9, 2009)

yuri said:


> Do you have website/link for it? I would really like to see it. Hoyme's are expensive but good and I may sell these if I like them.
> 
> Thanks


http://www.skuttle.com/makeupcontrol.html


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## yuri (Nov 29, 2008)

Thanks. Seems like their server is slow. Will try later.


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## n0c7 (May 15, 2008)

yuri said:


> You can do it that way. Size depends on the amount of BTU's of your furnace and water heater (if you have one in that room) and your local gas code. In the old days we used 1 sq.ft /100,000 BTU's rule of thumb. A 6 " round pipe would be good for that amount. You need to make sure that the pipe does not have kinks in it if you are using insulated flex pipe. Call your gas supplier and they can look it up in their code book.


I'm considering a Hoyme damper as well. I have a small enclosed furnace room with a natural gas furnace(mid efficiency) and a hot water tank. The room has a solid door on it and for combustion air there are two 6" fresh air intakes - one to a combustion pot on the floor which freezes the basement, and another high into the return air ducting.

Now, according to National Standard of Canada - CAN/CSA-B149.1-05:

*8.2.3* An outdoor air supply shall not be required for a single water heater with an input of 50 000 Buth (15 kW) or less within an enclosure or structure where there are no other appliances that require an air supply. 

So, theoretically, you could install the damper in a setup like mine as the water heater does not need an air supply by itself, only when the furnace runs hence the damper........ I'm going to run this by the City of Edmonton and see what their take is on it.


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## yuri (Nov 29, 2008)

As long as there is SOME way for air to enter that room, as the water heater and its chimney do need air. If the ceiling is open to the joists then there usually is no problem. If it is all drywalled up there I would still allow some air into the room. ALL gas appliances need air for combustion AND draft up the chimney. I have seen some VERY badly carbonned up water heaters and they will produce/spill CO and have no safety devices ie:rollout switch like a furnace to protect you.


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## n0c7 (May 15, 2008)

yuri said:


> As long as there is SOME way for air to enter that room, as the water heater and its chimney do need air. If the ceiling is open to the joists then there usually is no problem. If it is all drywalled up there I would still allow some air into the room. ALL gas appliances need air for combustion AND draft up the chimney. I have seen some VERY badly carbonned up water heaters and they will produce/spill CO and have no safety devices ie:rollout switch like a furnace to protect you.


In my case, the furnace room ceiling is open to the joists, but the rest of the basement has drywalled ceilings and insulation in the joists.

Would the crack under the bottom of the door be enough for the water heater?


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## yuri (Nov 29, 2008)

As long as a couple of joist space(s) is open to the rest of the basement and you have a 1" crack under the door you should be fine. However, I have seen newer airtight homes that are so tight that when the customer turns on a central vac, jennair power range fan and the bathroom fans you can downdraft a chimney. Obviously you should have a CO detector in your basement and one by your bedroom and buy the best kind you can afford.


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## n0c7 (May 15, 2008)

yuri said:


> As long as a couple of joist space(s) is open to the rest of the basement and you have a 1" crack under the door you should be fine. However, I have seen newer airtight homes that are so tight that when the customer turns on a central vac, jennair power range fan and the bathroom fans you can downdraft a chimney. Obviously you should have a CO detector in your basement and one by your bedroom and buy the best kind you can afford.


Half of the basement ceiling(joists) were left uninsulated as it was not necessary. Isn't that dead air, or do all the "cracks" from around the foundation allow air to squeeze through there?

I have Kiddie CO detectors. A CO detector installed in the furnace room(I keep it clean and do vacuum the furnace room, and have only once got a minimum reading of 11ppm over a 4 month period due to the initial firing of appliances) and have another one on the second level near bedrooms. Most expensive suckers the store had.


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## yuri (Nov 29, 2008)

It is impossible for me to safely give you advice as I do not know how airtight your house is. I had a new house built in Calgary and the builder told me that if I had ordered a more powerful kitchen range/exhaust fan (not sure of the CFMs) that the building code would demand that the furnace fan with a fresh air intake be interlocked with it to prevent downdrafting of the chimney. It is possible to suck enough air out of an airtight home with exhaust fans to cause a problem. That is why they put those open combustion air pipe and pots in new homes. My new home in Wpg has an airtight hiefficiency furnace and electric water heater and no chimney, and a HRV so I have no worries.


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## hvaclover (Oct 2, 2008)

Here's an old timer test you can perform to see if you have enough air exchange to maintain combustion air and draft: Turn on all the exhaust fans, clothes dryer ect. Close the door to the WH room and check with the flame of a candle at the WH draft hood to see if the the water heater is venting well.
Hold the lite candle flame just under the outer lip of the WH vent hood.

If there is a back venting occurring he flame will waver wildly and blow out. 

Wait five minutes and test again. If flame stays lite while positioned just inside the lip of the draft hood you are ok


http://www.enviro.com/images/manual...nstruction Freestanding Drafthood Adaptor.pdf


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## n0c7 (May 15, 2008)

I got a response back from Hoyme Manufacturing. They make combustion air dampers for the cold air. This was their response to my setup, and may be beneficial to the original poster:

Thank you for your interest in Hoyme dampers. 

Your 6" duct having a bucket on the floor allows outside cold air to continually flood your furnace room even when the furnace and the DHW fires are off. The answer is to install approved automatic motorized dampers which is a paying proposition as well as increasing comfort in your basement and the rest of your home. 

First the bucket is to be removed and the damper, which is approved for your combustion air supply, is to be mounted on the side of your furnace approximately 1 foot above the FLAME level. The damper I.D is 'HOM-0611-SF1'. The fresh air will then drop into the flame increasing the efficiency of your furnace. 

Your DHW is less than 50,000 BTUH and according to the B149 Gas Code does not require extra air during its firing. We do, however, have a Heat Limit Switch that will cause the damper to open after 30 seconds of firing if you feel it necessary, 

Your fresh air duct leading to the return air should also have a motorized damper which will open when the combustion air opens and both dampers will close to save energy when the fire is off. The damper ID is 'HAC-1610-OPC'.

Your new house will also have a designated ventilation switch which by code is to open the fresh air damper, turn on the furnace fan and turn on the exhaust fan simultaneously. An interface adaptor is, therefore, required. The ID of this adaptor is 'ADP-1101-05A'

A colored wiring diagram #5 is on our web www.hoyme.com under FAQ.

The city never got back to me on my request(typical). But this should answer most peoples questions regarding combustion air supply w/ cold air issues.


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## kenmac (Feb 26, 2009)

This would work for a furnace... But not on a water heater with a standing pilot.. There would be no electrical to tell damper to open when the WH fired


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## hvaclover (Oct 2, 2008)

It's just too much. The more electro mechanical devices the more to go wrong.

A simple Skuttle counter balanced damper would provide the same result with no electric parts what so ever.

Do you find the the electric product to be more desirable?


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## n0c7 (May 15, 2008)

kenmac said:


> This would work for a furnace... But not on a water heater with a standing pilot.. There would be no electrical to tell damper to open when the WH fired


See this part:

Your DHW is less than 50,000 BTUH and according to the B149 Gas Code does not require extra air during its firing. *We do, however, have a Heat Limit Switch that will cause the damper to open after 30 seconds of firing if you feel it necessary,*

So according to our gas code, your average hot water tank doesn't need air apparently...... and if you're paranoid like me, you can install this Heat Limit Switch.


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## n0c7 (May 15, 2008)

hvaclover said:


> It's just too much. The more electro mechanical devices the more to go wrong.
> 
> A simple Skuttle counter balanced damper would provide the same result with no electric parts what so ever.
> 
> Do you find the the electric product to be more desirable?


I'm not sure what the Skuttle is. I have not heard any better ideas aside from the mechanical damper yet. I've heard of one person I know that has done this conversion and had nothing but good things to say about it.

Their warranty isn't all that bad either:

The Products manufactured by *Hoyme Manufacturing Inc.* are warranted to be free from defects in workmanship and material under normal use and service and carry a limited warranty for a period of two years electrical and ten years mechanical.


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## hvaclover (Oct 2, 2008)

I gave you a link to the Skuttle site earlier in this thread. That Hoyme system sweet as it sounds will need maintenance of a higher level than what its worth for the application. Bearing can seize, swiches can fail ect.


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## kenmac (Feb 26, 2009)

n0c7 said:


> See this part:
> 
> Your DHW is less than 50,000 BTUH and according to the B149 Gas Code does not require extra air during its firing. *We do, however, have a Heat Limit Switch that will cause the damper to open after 30 seconds of firing if you feel it necessary,*
> 
> So according to our gas code, your average hot water tank doesn't need air apparently...... and if you're paranoid like me, you can install this Heat Limit Switch.


 

I don't know what B149 gas code is.. But around here a gas wh installed in a room /area wouldn't pass inspection if the deemed by the inspector isn't large enough to support combustion air / dilution air. & would be considered a confined space... confined space........a space whose space is less than 50 cu. ft. per 1000 btu per hr imput rating of all appliances in the room... If there is a clothes dryer in that same room ( doesn't matter if it's gas or elect. the combustion air requirments increase


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## yuri (Nov 29, 2008)

So far the Hoyme dampers have been INCREDIBLY reliable. Have not had to replace one yet. They close on the off cycle (powered closed) and open when no power applied. In other words they fail open and need to be driven closed. If the motor fails/strips you will still have heat. Any gas burning appliance needs air and air to have draft for the chimney so I would always make sure it gets it irregardless of the minimum code.


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## hvaclover (Oct 2, 2008)

yuri said:


> So far the Hoyme dampers have been INCREDIBLY reliable. Have not had to replace one yet. They close on the off cycle (powered closed) and open when no power applied. In other words they fail open and need to be driven closed. If the motor fails/strips you will still have heat. Any gas burning appliance needs air and air to have draft for the chimney so I would always make sure it gets it irregardless of the minimum code.



Does not matter. Too many moving parts is trumped by a product that has none and gives the same results.


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## lnlakes (Apr 24, 2011)

*question about fresh air dampners*

I am planning to build a home and need to know how I can assure enough fresh air in the house since it will be very tightly insulated. The ranch home is 1800 sq ft with a full walkout basement. The heating system is hot water radiant, w/high efficiency boiler. There will be a gas fireplace on the main level and a wood burning stove in the basement. Also, there will be radon abatement in the house (pipe w/blower exhausting to roof) which I understand requires the house to have slight negative pressure to work correctly. The home is located in the Thumb area of Michigan. 

Is there a recommended method for this situation? Thank you for your assistance.


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## yuri (Nov 29, 2008)

I deal with lots of negative pressure problems and would recommend a sealed combustion boiler that takes its combustion air from outside. Also a sealed combustion direct vent gas fireplace and NOT a wood burning stove. Read this post about draft problems with them. IMPOSSIBLE to maintain a slight negative pressure and not downdraft a stove. http://www.diychatroom.com/f17/down-draft-issues-woodstove-100436/


Your local contractors should know how to setup the radon fan properly and give you advice. You will need to bring in some fresh air equivalent to the CFMs it is exhausting and they know that amount. If the house is very airtight you may need a HRV or ERV heat recovery or energy recovery ventilator to exhaust moisture/cooking smells etc. Google those terms or visit Lifebreath.com
http://www.lifebreath.com/


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## lnlakes (Apr 24, 2011)

ok. thanks. the boiler will be sealed. my biggest concern about the new house is that it won't get the minimum needed air changes daily during the winter. I think outside air is going to be needed. 

funny that people have so much trouble with wood stoves. I've had one for over 20 years and never had smoking issues like these. I learned early though that watching the fire caused problems so I light it and close it up until the stack temp drops enough to signal needing more wood. the stack does go through the center of the house so maybe that helps too. this will be used only occasionally since it is in the basement. if needed, a window could be cracked for that. 

the major concern is the general air quality.


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## yuri (Nov 29, 2008)

Lennox HRVs are very good and made by Lifebreath and yes you do need some ductwork or a basic airhandler and ducts. No way to get around that. I see VERY airtight R2000 homes ( google that) and have a very airtight home myself and you may be VERY sorry if you do not have some ductwork/ventilation system. VERY expensive and difficult or impossible to add later w/o ripping out ceilings etc so I would seriously consider it now. We want to have very airtight homes but not do the necessary work/buy equipment to deal with the problems they create. For the first 2 yrs you will be getting sick with off gassing from the paint/carpet etc etc. You can put an airhandler in the attic. I guess you do not want air conditioning either? Why not go with a forced air furnace, Lennox 3 stage SLP with variable speed energy saving ECM motor and a HRV. Just as comfortable as hot water heating, 98% efficient and you can put in AC later if you want. Only advantage to h/w heat is the comfort IMO and those 3 stage/modulating furnaces can easily match that now that the technology is here. Not sure about your climate but heat pumps are a good efficient alternative and we have several heat pump experts here and a Lennox guy (Marty) who has one and can give you advice.


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