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Old 02-12-2012, 03:26 PM  
dellposter
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Default fresh air intake draft

I have a mid nat gas forced air furnace and gas hot water tank. The hot water tank directly exhausts outside, while the furnace has a fan to push the exhaust up a chimney (no draft hood) i also have a natural gas fireplace that has b-vent. I have been fighing trying to keep my utility room warmer as my kids bedroom is directly above. The only cold source i found is the fresh air intake. It is currently a 4" insulated pipe that goes down to the floor then back up 3' like a p trap. It originally just hung in the air, and i thoght the p-trap would help but it doesn't. It has cold air coming from it even when everything is off. I am too nervous to damper it anymore casue there is the chance that all appliances could run at the same time. Should i worry about doing this, or is there any other suggestions on what to do? Oh ya i have a venmar HRV. it has a single motor so whatever it oushes out it draws in so i assume its balanced. I even shut it off and still have the cold air issue. All new windows in the house. I had it tested and its a pretty tight house.



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Old 02-12-2012, 07:51 PM  
Dionysia
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The HVAC folks know much more about this than I do I am sure. But, I'll chime in anyway. It would seem to reason that a P-trap down to the floor would not keep cold air out since cold air sinks. As the air enters the house, warms and rises, I would think it would come out of your pipe, sucking more cold air behind it.

The exhause vent for our furnace points like an upside down U, keeping the cold air from rising up into the pipe and into the house. Just my 2 cents.



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Old 02-12-2012, 09:13 PM  
paul52446m
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Quote:
Originally Posted by dellposter View Post
I have a mid nat gas forced air furnace and gas hot water tank. The hot water tank directly exhausts outside, while the furnace has a fan to push the exhaust up a chimney (no draft hood) i also have a natural gas fireplace that has b-vent. I have been fighing trying to keep my utility room warmer as my kids bedroom is directly above. The only cold source i found is the fresh air intake. It is currently a 4" insulated pipe that goes down to the floor then back up 3' like a p trap. It originally just hung in the air, and i thoght the p-trap would help but it doesn't. It has cold air coming from it even when everything is off. I am too nervous to damper it anymore casue there is the chance that all appliances could run at the same time. Should i worry about doing this, or is there any other suggestions on what to do? Oh ya i have a venmar HRV. it has a single motor so whatever it oushes out it draws in so i assume its balanced. I even shut it off and still have the cold air issue. All new windows in the house. I had it tested and its a pretty tight house.
Where is this 4" pipe coming from? Is your furnace on the main floor or in the basement? do you have a craw space?
One thing you could try. Take a 5 gal. bucket setting on the floor, cut the 4" pipe so it hangs in the bucket about 4" off the bottom. This will make a heat trap so it will only pull air in when you have a small vacuum on the room. Paul.
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Old 02-13-2012, 01:15 PM  
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the furnace is located in the basement. which is used as living space as well. The 4" line travels stright up along the floor joists approx 8' then straight outside through the wall. It ends up a little over 3' off the outside grade. Oustide There is a hood with a screen, so wind can't deirectly blow into it

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Old 02-13-2012, 01:59 PM  
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Paul's explanation is just what I have and my intake vent goes up about 20' up and we have -10F to -20F in the winter and no problems or excessive costs. It is a normal situation here.

The key is a furnace/utility room that is reasonably well closed with a door and without a vent/louver in the door. This makes it draw only when required.

Dick

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Old 02-13-2012, 05:38 PM  
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Originally Posted by dellposter View Post
I have a mid nat gas forced air furnace and gas hot water tank. The hot water tank directly exhausts outside, while the furnace has a fan to push the exhaust up a chimney (no draft hood) i also have a natural gas fireplace that has b-vent. I have been fighing trying to keep my utility room warmer as my kids bedroom is directly above. The only cold source i found is the fresh air intake. It is currently a 4" insulated pipe that goes down to the floor then back up 3' like a p trap. It originally just hung in the air, and i thoght the p-trap would help but it doesn't. It has cold air coming from it even when everything is off. I am too nervous to damper it anymore casue there is the chance that all appliances could run at the same time. Should i worry about doing this, or is there any other suggestions on what to do? Oh ya i have a venmar HRV. it has a single motor so whatever it oushes out it draws in so i assume its balanced. I even shut it off and still have the cold air issue. All new windows in the house. I had it tested and its a pretty tight house.
Lets start all over again. You are calling this 4" flex pipe a fresh air intake. A fresh air intake is a 4" pipe that comes from out side and goes into the return air of the furnace. It would be there to bring fresh breathing air into the home.
Now we have another thing called burner make up air. This is to give air to let the burners and natural draft stacks work. .
So you say your water heater is power draft to the out side, and does it bring in its own burner air in? Does your furnace have metal pipe and a fan, and does it go into a chimney to the out side?
Is your furnace room sealed off with a solid door on it?
What is the BTU rating of the furnace?
How many sq. feet is your furnace room?
The reason i am asking these question, is if your furnace room is tight and you have a fan assisted furnace, then the 4" pipe is not large enough.
Where is this fire place at in the house? Paul
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Old 02-13-2012, 08:30 PM  
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paul and others -

Just to clarify, what I described was burner make up air or fresh air supply and not a vent. We do not have an exterior vent for fresh air. The 5 gallon pail does wonders. this is common for all homes in the development.

My utility room works well even though it is not 100% tight (leakage under the door) and the outside air is not sucked into the utility/heating room unless there is a draw from the furnace or gas water heater, but when I switch to a gas dryer, there may some more for a few minutes every other day.

Dick

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Old 02-13-2012, 09:20 PM  
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Lets start all over again. You are calling this 4" flex pipe a fresh air intake. A fresh air intake is a 4" pipe that comes from out side and goes into the return air of the furnace. It would be there to bring fresh breathing air into the home.
Now we have another thing called burner make up air. This is to give air to let the burners and natural draft stacks work. .
So you say your water heater is power draft to the out side, and does it bring in its own burner air in? Does your furnace have metal pipe and a fan, and does it go into a chimney to the out side?
Is your furnace room sealed off with a solid door on it?
What is the BTU rating of the furnace?
How many sq. feet is your furnace room?
The reason i am asking these question, is if your furnace room is tight and you have a fan assisted furnace, then the 4" pipe is not large enough.
Where is this fire place at in the house? Paul
Its a burner make-up air. The furnace room is 300sqft. total living space is 2500, 1250 up and down. I think its 80,000 btu The hot water tank power vents out the wall (pvc), but does not bring in fresh air. The furnace power vents up a sealed chimney (metal 4" pipe and fan), and does not bring in fresh air. The gas fireplace is in the basement 30' away, and does bring in its own air, and is hardly used. Also the furnace room isnt tight. I usually have the door open. If the door is closed the floor joists from the upper level are open into the next room which is open to the rest of the basement
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Old 02-14-2012, 05:42 AM  
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Quote:
Originally Posted by dellposter View Post
Its a burner make-up air. The furnace room is 300sqft. total living space is 2500, 1250 up and down. I think its 80,000 btu The hot water tank power vents out the wall (pvc), but does not bring in fresh air. The furnace power vents up a sealed chimney (metal 4" pipe and fan), and does not bring in fresh air. The gas fireplace is in the basement 30' away, and does bring in its own air, and is hardly used. Also the furnace room isnt tight. I usually have the door open. If the door is closed the floor joists from the upper level are open into the next room which is open to the rest of the basement
If i was you i would just put the pipe in the bucket, because that does work.
Do not seal up your furnace because that 4" pipe is not even half of what you need for burner air. Paul


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