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I live in a house that was built in 2000. I’m puzzled about the way air flows in two instances:
1. When the (oil, hydronic heat) furnace is running, there is positive pressure in the basement (air flows into first floor through crack under basement door; air flows out through vent in floor of fireplace).
2. When fire is burning in fireplace, air/smoke is sucked down through a vent in the back of the fireplace floor.
The fireplace has two openings on the floor, one in the front and one in the back. They appear to go to plenum in the foundation of the fireplace. There are two aluminum doors in the basement that open into this space. If you open one of the aluminum doors while the fireplace is running, there is a strong suction through the door. There is a small aluminum vent on the outside of the chimney. There is a CO detector right above the furnace.
Regarding 1), I would have expected the furnace to draw air, not produce it.
Regarding 2), I would have expected that the fireplace vents would be a cold air intake, not a vacuum. The fireplace draws fabulously, but generates virtually no heat; I suspect partly because it’s sucking huge amounts of air out of the house.
I didn’t build this house or see it built, and I’ve never had an oil furnace or a tight house before, so all of this is new. Can anyone help me sort this out?
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Pete,
I can't think of a reason (maybe a prolonged senior moment???) but that positive pressure in the basement bother's me.
I think you should have it checked out ASAP
One possible explanation is that the flue is missing a connection or is blocked.
When we heat the combustion air, it has to expand and it will create additional pressure in the space it's in to some extent.
Assuming the CO detector hasn't gone off (is it an alarm only or have a digital readout?), it doesn't mean you might not end up with a serious CO problem tomorrow.
Your boiler probably isn't producing a lot of CO, mainly CO2. If the basement gets enough CO2 buildup, however, the boiler flame could start being starved of available oxygen to support the clean burn and all of a sudden the boiler would turn into a big time CO machine.
For example, if a cold snap hits tomorrow and lasts, and the boiler is running longer than it has been, the balance may shift and cause CO problems.
I don't know how likely this is; but think it's a possibility which should be checked out by a competent HVAC technician.
Is the humidity in the house high? More condensation on the windows than you'd expect? If so, its and additional indication of flue gases not being properly vented.
*Another possibility (probably more likely) is that there is too much opening in the distro pelnum in the basement and little of no return.Check 'em both.
*Bob,Not sure what this means. Can you give me a basic layman's understanding? I'm a mechanical engineer, so it doesn't need to be too basic.Pete
*To help me understand what you have:-Where is the boiler(you did say hot water baseboard heat didn't you)? Garage, basement, utility room?-Does the boiler have an outside combustion air source? Or, does it just get its' combustion air from ambient air in the house?-How do you know it is "positive pressure" and not just air flow to the boiler? Assuming the boiler is in the basement.-Have you looked at the flame in the fireplace when the boiler burner is lit? What does the flame do? Change color, change pattern, etc?
*-Where is the boiler(you did say hot water baseboard heat didn't you)? Garage, basement, utility room? Yup, hot water baseboard. Furnace in basement next to base of chimney. Flue goes into chimney.-Does the boiler have an outside combustion air source? Or, does it just get its' combustion air from ambient air in the house? Appears to be ambient. I only see the flue.-How do you know it is "positive pressure" and not just air flow to the boiler? Assuming the boiler is in the basement. By positive, I mean air wants to flow out of the basement when the furnace is running.-Have you looked at the flame in the fireplace when the boiler burner is lit? What does the flame do? Change color, change pattern, etc? Fireplace doesn't seem to change. When the fireplace is not lit though, there is a puff of ashes from the fireplace vents when the furnace fires up.
*Pete,"Not sure what this means. Can you give me a basic layman's understanding?"Ahhh, if you're looking at my reference to the distribution plenum, it means you've spotted by failing to recall that it's hydronic, and not a forced air system - please disregard that 2nd message.