Make up air for standard boiler?

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Old 12-18-08, 06:29 AM
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Make up air for standard boiler?

I have a question about incomming air for my boiler's burner. It is a standard boiler with a down draft diverter on the flue. Above the diverter there is an automatic damper, which opens before the boiler fires.

How much incomming air is needed? Would it be advisable to add an automatic fresh air intake somewhere in the basement? Maybe use a similar automatic damper as the boiler has now, wired into the existing damper so they open together. Cut it into the wall and put a little rain hood on it w/ a screen. What do you think? Is it nessasary? The house has been sealed up much better in recent years, so much of the natural air leaks of an older house have been sealed off. I fear the boiler draft causing negative pressure in the house which my draw fireplace smoke into the room (which seems to have happened before I started opening a basement window when I have a fire lit).
 
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Old 12-18-08, 10:02 AM
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Dedicated make up air is a good way to go. For the required volume there is usually something in the I & O manual for the particular boiler. You may be able to (or should be able to) find the manual on line for your system.

As for using an auto-damper on the make up entrance, it will need to be larger then the one currently on the boiler flue. The reason is that the flue has draft from the chimney. Which moves the flue gases quickly out. The make up air is only going to move from the low level pressure difference of the burner room. So the opening needs to be larger.

Maybe a fan shutter arrangement would work for the make up air damper. These fit a square or rectangular opening.

Al.
 
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Old 12-18-08, 12:38 PM
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You say a fan blowing into the basement? I hope to not need a fan. I will get my model # and check online for the manual. I thought I saw a formula for BTU's x flue size to determin the fresh air opening required. I'll look it up.
 
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Old 12-18-08, 02:15 PM
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Didn't mean a fan, just the shutters that are used for them. There are both gravity shutters that the fan blows open, but there are also motorized shutters. A set of motorized shutters may be the ticket.

Al.
 
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Old 12-18-08, 07:45 PM
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Not sure the exact amount you need ... but it was something like 100 sq in for every so many BTU, wasn't it? Maybe someone will remember it...

Some ideas about running a piece of vent tubing into a bucket or a garbage can to form a 'heat trap' have been thrown out there recently... idea is to run the vent pipe to the bottom of the bucket or can. The container will fill with cold air and then the air flow pretty much stops (or so it's said)... until the burner kicks on and changes the pressure in the room. It will draw the air it needs. You can also chill beers in the bucket.
 
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