Running Furnace Fan...creating neg pressure in house?

[poordamocles]

I have a basic question: On my forced air gas furnace, if I run the fan alone (no heat), does it force some of my house air out of the chimney? Or would there be a damper stopping this from happening?
Thanks.

 

[JohnD]

If it was a gas boiler in the UK (this is a UK site) you would have to have fresh-air-in ventilation for such a boiler, of a size that could supply it without needing to suck air from the house, and so could not create negative pressure.

this is usually a hole in the adjacent wall, but sometimes ducts are used (this prevents draughts)

 

[Onetap]

I have a basic question: On my forced air gas furnace, .......

Try asking here;
http://forums.invision.net/index.cfm?CFApp=2

 

[poordamocles]

Okay, I'll try the other link; thanks. My situation is the same as in the U.K., though. I have a fresh-air intake near the furnace, but I'm experiencing some problems I think may have to do with negative pressure. Is there an easy way to test whether you have negative pressure in your house, or do you have to guess by the way your appliances are acting?

 

[JohnD]

We have defined Air aperture sizes for each boiler; calculated so that the suction won't occur (I believe the reason is so that inadequate airflow won't cause poor combustion and possible CO fumes into the house)

I would have thought your manufacturer would have a table of sizes for boilers, possibly a current model of equivalent rating if yours is old.
If you have neg pressure you would notice it by cold air rushing in through any gaps or holes, e.g. round the doors, even when there is no wind on that side.

There is always a slight upwards flow, due to heating convection, inside a building, and you may have warm air escaping into the roof space.

 

[poordamocles]

Yes, my attic hatch-cover is allowing warm air to leak out of the upstairs. I just discovered that with a stick of incense. There is a bathroom fan up there as well. I'll seal them both up and see if it helps the situation. This fresh-air intake in the basement is a real problem, though. I'd like to keep it plugged because it lets in so much cold air that you need to wear winter clothes down here. Doesn't seem logical: I bought a new higher-efficiency furnace, then had to let the winter into my basement in order to run it. Should have stuck with my old model and saved a bunch of money.

Thanks for your help, though. Appreciate it.