Adding Make up air to boiler

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Old 03-20-11, 03:55 PM
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Adding Make up air to boiler

I have a oil fired boiler in a utility room in my basement. I would like to add some make up air to this room so it is not pulling air from the rest of the finished basment space or the rest of the house. The boiler has a direct vent with a power venter and pulls air into it through the burner directly from the room. Can I install an inlet on the side of the house that come in with pvc and terminates approx. 6 inches off the floor.... possible put a bucket under this as a "trap" for the cold air. Or should I bring this pvc right down to the floor, use a 90degree elbow and then pvc it back up to about 8 inches off the floor so it has a built in trap? I plan on insulating the pvc also. Similar to this:
Combustion Air
See section on Duct outside air to floor in furnace area

Can this be installed on the same wall as the power venter, or would it suck in the vented gases into the house? I could try to install this on the from of the house just above the sill plate, this way its on a different side of the house away from the power venter.

Please let me know if this would is a good method for adding make up air and how much cold air would get into this room using this method?
 
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Old 03-20-11, 08:28 PM
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Generally it is preferable to bring combustion air in on the same wall as the the exhaust. There are specific installation instructions pertaining to spacing between power vents & air intakes. These instructions come with the power venters.
I've never installed one but from everything I've read, the pipe into a bucket seems to be the preferred method. Make sure the intake is above the snow line & has a cover (similar to a dryer hood) or a down turned elbow. A screen is also a must have to keep out birds.
 
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Old 03-20-11, 09:56 PM
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Your likely going to want a 5 or 6" vent pipe.
Since the exhaust is under pressure that pipe sizing is smaller.
Since the inlet will be under a potential negative pressure it needs to be bigger in order to minimize the loss thru it...
To small and you will still be burning room air, but don't make it too big.
 
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Old 03-21-11, 01:03 PM
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Is it ok to use pvc for this, or should I use aluminum in case I want to upgrade to a fan in a can in the future? Also does anyone know why this has to be on the same wall as the power venter? The boiler is in a corner of the house so if i were to pipe the fresh air approx 2 feet away from the venter I am afraid of brining in gases from the venter especially on windy days. What is the reason that this cannot be on the other wall of the house where it would be more shielded from the exiting gases? It is only a difference of about 4-5 feet if you measure around the corner of the house.
 
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Old 03-21-11, 01:11 PM
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With the air not being piped directly to the burner, it really doesn't have to come from the same "atmospheric zone" (wall) as the exhaust exits. Since you are familiar with the Fan-In-A-Can, that's the route I would go. You can interlock it with the venter. By doing so, you are only bringing in outside air when the venter is running.
 
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Old 03-21-11, 03:54 PM
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Also does anyone know why this has to be on the same wall as the power venter?
Pressure differences. Wind blowing across the house can cause a higher pressure on one side and a lower pressure on the other.

As Grady said, it won't matter with the fan in a can because it's not 'booted' right onto the burner.

You need to research what the manufacturers specs as separation distance between the inlet and the outlet... I don't think 2' is nearly enough.
 
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Old 03-21-11, 04:25 PM
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Yeah, with an induced draft such as that (power venter) the pressure switch is not sensitive enough to become blocked out by different pressure zones.
I would think you can draw your make up air from anywhere, further from the vent the better.
If there are manufacturers spec, follow them.
 
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Old 03-23-11, 06:44 AM
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Whose burner do you have? Most offer kits to connect directly to the burner so you do not need to do any of the options you mentioned. If it mounts directly to the burner it is usually only 4" pipe.
If you are dumping it into the room you need to calculate how much combustion air you need. This is not hard, you need to bring in whatever is not supplied by the room.
Example, if the room is suppling 40% than 60% needs to come from the outdoors.
The best way it connecting directly to the burner. You can use a smaller pipe and the fan pulls in the combustion air as needed. If using this application the combustion air should be on the same wall as the vent.
See link and click on Combustion Air Calculation
Technical Menu
 
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Old 03-23-11, 02:15 PM
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I agree that connecting directly to the burner is a good way. My thought process was that when you add in 3 bathroom vent fans and a dryer in a well sealed house I need air from somewhere. I figured that brining air into the room from the outside is the best way to go (not a boot that just draws air when the boiler runs). That was all these other appliances have something to draw and wont use up all the house air.
I went with a 6 in pipe based on the BTU calculations down to about 7 in off the floor. Its about 30 degrees here and the room doenst really feel any different in temp. Maybe a degree or two cooler. I do feel like the entire basement has a "fresher" feel to it but it may just be in my head.
 
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Old 03-23-11, 02:31 PM
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I forgot to add that I also have a power venter also sucks out alot of air. Those boots only go to the burner and do nothing for the air that is lost from the venter.

One last question I have is the previous owner put a door sweep on the door to the basment. Should I remove this to allow air to circulate better down the stairwell and not just sit behind the door and also for when fans or dryers are running upstairs? I cant see that stop doing much for heat loss on the 1st floor seeing its a hollow core door.
 
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Old 03-23-11, 04:03 PM
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If the venter is connected to the boiler it would pull air in thru the burner intake, thru the boiler, then out the exhaust. IF the pipe from the boiler to the venter has a barometric damper (draft regulator) in it you would also be pulling out room air. Without the barometric, you are only pulling air thru the burner.
 
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