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Old 10-14-2010, 10:01 AM   #1
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Fresh Air Intake for Furnace Room. Help Needed


Hello,

I have a question that I am hoping someone can help me with. I have a 70kBTU Hi Efficiency furnace and a 33kBTU conventional water heater. The Hi-Efficiency Furnace has its own intake and exhaust and vents through a side wall but the Water Heater is vented through the chimney.

I am told I now need to install a Fresh Air Intake so I don't get the possibility of back draft from the chimney (The only think vented through the chimney is the water heater).

I investigated and found that I do have a Fresh Air Intake installed into my cold air return (it is a flex duck 3" in diameter) and attach directly to my cold air return (about 9' away from the furnace). But the HVAC installer said he wants to leave that in place but run another 4" diameter duct from the outside to my furnace room and make it into a U-Shape similar to the letter "J" about 6" off the ground next to the furnace.

My question is, if I add that new 4" dia pipe would that not bring in a ton of cold air into my home since I already have a fresh air intake installed into my cold air return. Or should I just close up the fresh air intake into my cold air return and just run the 4" dia duct to my furnace room alone as the HVAC tech suggested??

I live in Canada and it get to be -30 around here in the winter. Can some one help me with this one, how do you size a fresh air intake anyways maybe 4" is to big or to small, I just don't want that freezing air coming into my home?????

Samantha

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Old 10-14-2010, 10:31 AM   #2
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Fresh Air Intake for Furnace Room. Help Needed


Fresh air intake on the furnace return is brought in to add fresh air to the home. It sounds like he wants to bring in fresh outside air for combustion of the wh. Some areas require this & some don't . The ones that don't require fresh outside air, require that the area which the appliance is installed has enough combustion / dilution air. Could be that canada requirs this.. There is a guy from canada on here. Maybe he can provide some info for your area when he checks in


Last edited by kenmac; 10-14-2010 at 10:36 AM.
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Old 10-14-2010, 10:50 AM   #3
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Fresh Air Intake for Furnace Room. Help Needed


Thanks kenmac, so the line that runs into my cold air return mixes fresh air with the furnace but the additional 4" dia duct to the Furnace Room is for combustion of the water heater ONLY since the Hi-Efficiency furnace is vented outside?? But my water heater is only 32400 BTU does it really need a 4" dia pipe how did he size that unless he is considering the furnace BTU's as well but I would probably think you would not use the BTU of the Furnace since it is a Hi-Efficiency. Am I right in my thinking, I just think this pipe is not necessary?
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Old 10-14-2010, 12:01 PM   #4
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Fresh Air Intake for Furnace Room. Help Needed


Samantha,

I am in Edmonton Alberta so I undestand your pain. From talking with contractors I believe it is code to have a seperate pipe in to the furnace room with a pot on the bottom. This lets fresh combustion air in to the furnace room. My friend has a High Efficiency furnace in his place and his conctractor said the same thing, it is still required by code even though the furnace is outfitted with a direct outside line for combustion air. With how cold it gets outside I would say it has something to do with the draft in the chimeny for the water heater, you wouldn't want back draft in to your house.

I was concerned as well with the cold air coming in, I watched it last winter and it does let in cold air however it isnt overly noticable. If you are really concerned, Hoyme manufacturers electric dampers for both the fresh air in take to a combustion pot as well as to your cold air return. These are apparantly certified to meet code. They open up when the furnace comes on and close when it is off, preventing a lot of that cold air from entering the home.
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Old 10-14-2010, 01:04 PM   #5
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Fresh Air Intake for Furnace Room. Help Needed


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Originally Posted by samantha.77 View Post
Thanks kenmac, so the line that runs into my cold air return mixes fresh air with the furnace but the additional 4" dia duct to the Furnace Room is for combustion of the water heater ONLY since the Hi-Efficiency furnace is vented outside?? But my water heater is only 32400 BTU does it really need a 4" dia pipe how did he size that unless he is considering the furnace BTU's as well but I would probably think you would not use the BTU of the Furnace since it is a Hi-Efficiency. Am I right in my thinking, I just think this pipe is not necessary?

The outside line to the return air is only to bring / circulate fresh air into the home. It has nothing to do with combustion
If your furnace uses a 2 ( PVC) pipe system . 1 is for exhaust & 1 is for combustion air. If that's the case , outside air may be needed for water heater .. It all depends on what's required in your area

Last edited by kenmac; 10-14-2010 at 06:14 PM.
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Old 10-14-2010, 05:54 PM   #6
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Fresh Air Intake for Furnace Room. Help Needed


Where do you live Samantha and how old is your house. The Hoyme damper will not work with a gas water heater as it needs to be interlocked to the gas valve electrically with a furnace. Impossible with a water heater.

Your contractor is talking about a combustion air supply pipe which you may or may not need depending on age of house etc.
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Old 10-14-2010, 08:45 PM   #7
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Fresh Air Intake for Furnace Room. Help Needed


if the HWH is a regular burner with no induced draft as the furnace the rooms temperature will make a natural draft up th heaters flue in the off cycle .then when it runs it will get the basement air and pull nothing fron the furnace ID setup.any outside ducts dropping below the ground level into the basement will chill it out with those temps in the winter
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Old 10-15-2010, 12:37 PM   #8
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I live in Winnipeg, Manitoba and the home is 50 years old with poured concrete foundation but has been updated extensively over the years has an energy rating of 78, good windows, sealing etc. I do have a gas conventional water heater that is the only thing venting through the chimney. I think the 4" diameter insulated duct he wants to run into my furnace room is for the water heater combustion, he says it will also help reduce the humidity in my home. I don't know how the pipe will reduce the humidity but that is the information he is telling me. I guess if I need it then I will let him install it.
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Old 10-15-2010, 01:13 PM   #9
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It depends on haw large the room is. You need xxx amount of combustion air for xxx btu. If it's a small room & no air to get in for combustion. Then you may need the vent
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Old 10-15-2010, 07:04 PM   #10
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Fresh Air Intake for Furnace Room. Help Needed


A Hometown gal eh,

I doubt VERY much that you need that pipe with the age of your house. I have installed high eff. units for 32 yrs in Wpg and we very rarely had to add a combustion air pipe in your age of home. Reason being that the vapor barrier in homes then was poorly installed, not glued to the joists like they do now so you will always have enough air infiltration to take care of a small BTU appliance like a water heater. Only if you have a large powerful JennAir cooktop fan and central vacuum running at the same time can you depressurize your house. Houses built in the last 20 yrs have to have that pipe by code as they are tight. With the installs we do now 98% of the people convert to a electric water heater and cap off the chimney to make the house more airtight. Costs the same to heat water here with elec as gas. Gas tanks last 6-8 yrs and cost close to a grand installed. Elec last longer so that is what I would suggest. Get 2 new CO detectors. Put one in the basement stairwell and 1 by your bedroom and you should be safe.

If you have the outside of your house redone with Tyvek wrap or have the stucco elastomerically sealed (rubberized spray on stucco paint and coating)then your house will be tight and you may need some combustion air.
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Last edited by yuri; 10-15-2010 at 07:09 PM.
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Old 10-15-2010, 07:54 PM   #11
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Fresh Air Intake for Furnace Room. Help Needed


Based on the information you have provided no outdoor air supply is required. Code states that water heaters under 50 MBTUH don't require an air supply (B149.1 section 8.2.3).
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Old 10-15-2010, 10:23 PM   #12
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Based on the information you have provided no outdoor air supply is required. Code states that water heaters under 50 MBTUH don't require an air supply (B149.1 section 8.2.3).


That would depend on location.. IFGC 304.1 - 304.12list combustion, ventilation, dilution air requirements that we have to follow
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Old 10-16-2010, 09:18 AM   #13
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That would depend on location.. IFGC 304.1 - 304.12list combustion, ventilation, dilution air requirements that we have to follow
OP is in Canada, hence the use of B149.1.
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Old 10-16-2010, 09:26 AM   #14
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I wonder who supersedes who in the Great White North. Local building codes or gas code? I don't get involved in new home construction but know that in Calgary the furnace has to be interlocked by building code to run the fan with a fresh air intake if the kitchen exhuast fan is over 100 cfm or some such size. That may not be in the gas code?
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Old 10-16-2010, 09:47 AM   #15
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OP is in Canada, hence the use of B149.1.

I had no idea what B149.1 was. That's why I said all areas are different . I don't even know who all goes by the IFGC. Most of the towns around aren't even up to date on the IFGC. some still use 2003 while others use 2006. I don't know of any that are using 2010 code

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