indoor boiler makeup air

[nctacoma]

I am curious why indoor wood boilers don't have a dedicated makeup air port that can be connected directly to the outside air via pipe like most new wood stoves have the option to? This seems like it doesn't make too much sense to me. Is there a good reason?

I have spent the past few years upgrading my attic, kneewall, and basement insulation and tightening up my house as much is as feasible. The guy I am buying my boiler system, when asked about makeup air, he said they normally just run a 6" duct from the outside to an area near the boiler to provide the air if the house is too tight for it to just come in through cracks and seams.

Any thoughts? I don't want to introduce a whole lot of cold air in the winter , seems sort of counterintuitive, but I also want it to draft right and burn well. Any ideas on how to vent the units but not sacrifice heat?

 

[alaskawild]

nctacoma...

Yes almost all manufacturers do not do anything about a direct combustion air connection sadly. I have field fabricated a few connections. If you are running a 6" vent for combustion air use one of these air dampers! http://www.supplyhouse.com/Honeywell-EARD6-6-Round-Motorized-Fresh-Air-Damper-DH90-13233000-p
Without it you do have a ton of unwanted air entering your building!

 

[PassionForFire&Water]

introducing sub-zero outside air will kill your combustion efficiency.
So, ... not a good idea.

 

[alaskawild]

You must have a proper amount of combustion air for a correct burn. We have been using outside combustion air (down to -60F) for years here. As temperature of air drops it becomes more dense. Physics at play here. Dense is good! Think about airplane performance at altitude. Temps are even lower than -60F and there is no preheating of intake air.

 

[heaterman]

There really is no choice in the matter. Your boiler, regardless of the fuel used, needs a neutral draft environment in order to function properly. That means enough air must be coming into the space to not only supply combustion air but also avoid a negative pressure situation in the boiler room. Whether that comes through cracks and crevices in the house or a dedicated combustion air duct is immaterial. Enough make up air has to be there.

 

[maple1]

I leave a basement window, that is located right behind my boiler, open just a small crack.

 

[velvetfoot]

alaskawild, I didn't know such a thing existed! Thanks for the link.
I have an automatic flue damper by Field Controls on my oil boiler, but it doesn't seal near as well as some of the reviewers noted for this fresh air damper: a foam seal!
With that damper, you wouldn't need a trap in the duct like I've read that folks far up north need.

 

[flyingcow]

Interesting thread. My boiler room is an insulated 8x12 room inside of a loosely insulated 24x36 garage. As time goes on I keep tightening up boiler room. Overlooked something, building shifts, etc. Seems to a moving target at times. Room is pretty tight now. Recently started smoking into room a bit upon start up. But I'm to the point now I am going to install a basic dryer vent in wall of boiler room, that will vent into garage. May need to weight flapper down with a sheet metal screw or two, making sure the flapper will open up when draft fan opens up, close good when off. That may involve sippn a cold one or two, studying the flappers performance.

Note, I'm not getting smoke roll out out the boiler loading door, just pipe and chimney clean out door.

 

[Coal Reaper]

http://www.supplyhouse.com/Fantech-COM6P-COM6P-Plastic-Supply-Exhaust-Hood-Combination-Pair-6-Duct
i have one of these sitting on the shelf for when i finally get doors on the room my boiler is in. i will just pop this in the wall and it can pull in air from the barn, which is about as air-tight as a corncrib.

 

[atvalaska]

http://www.supplyhouse.com/Honeywell-EARD6-6-Round-Motorized-Fresh-Air-Damper-DH90-13233000-p I got me one of these .....(thanks akwild!) ... I put it near the ceiling( 7'8"') on my boiler shed air will come across the ceiling /mx with the warmer air then down to the intake fans at 12" and 18" off the floor. well that's the idea never had trouble in the pass with cold air to feed a fire ...now a cold fuel/ source ...that's a different story

 

[alaskawild]

velvetfoot...

You would like this unit. I've tried them all and this is the cats meow! Just get a 24volt 40va transformer and wire it to a line voltage source such as a blower fan and you are in business! Air trap configurations are a total waste of time! - 60 degree air is so heavy that it is not practical to try and design an air trap. Yes I know it's a dry cold! It's darn cold
You guys should checkout atvalaska boiler building. I had the pleasure of taking a look-see at his boiler. His boiler building is a repurposed walk in cooler! Now that is one tight unit!! I hope you will post some pics And you are correct about cold fuel sources. Especially fuel oil! As viscosity changes, burn rates take a huge dump. On the Slope and here in Fairbanks many systems use day tank arrangements to preheat fuel. As for propane you better bury your tank here and oversize for your reduction in it's ability to gas off. -44 degrees and you are not gassing. Burying your tank here will keep you at about -22 which works.

 

[jebatty]

Another idea which works well:

Make-up Air

 

[avc8130]

My WoodGun has an intake pipe that could be easily plumbed outside.

Makeup air is very important. There are calculations for how big the room needs to be before you have to add purposeful venting. Flyingcow, I would bet your installation would not meet code without a significant makeup air vent.

A 4" dryer vent won't do much naturally unless it is connected directly to the boiler inlet. When I finished my basement and built a room around my old NG furnace (room was 10x20) the inspector came in and made me put 2 18x18 louvered vents in the wall, one at the ceiling and one at the floor, for makeup air.

ac