Hello,
I have a 1.5 story bungalow in Minneapolis with a full basement. One room in the basement is finished. The house is heated by a high-effeciency forced air furnace that was installed before I owned the house. It is located in the basement in a large room.
Next to the funace, there is a make up air duct that is apx 6″ in dia and goes directcy from outside to within apx 1 foot of the floor. LOTS of cold air continuosly flows into my basement through thiis vent. I assume it was installed to ensure the house doesn’t have “backdraft” issues, but it seems a bit excessive. In fact, I question if it is nessisary at all. I have seen much tighter houses that have no such vent.
Comments? Should I get an HVAC guy out to look at it and determin if this vent can be removed? I don’t think it is doing good things for my heating expense.
Thanks,
Erik
Replies
look here for options and sizing on combustion air.
http://www.codecheck.com/pg21_22mechanical.html#combustionair
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Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
If your furnace needs a makeup air duct from outside, then it's not high efficiency as I know it....and even (in general) older houses have enough leakage that they don't need dedicated makeup air for the typical furnace...
Do you have any other "combustion appliances" (gas water heater, gas dryer, gas range, gas fireplace)? If so, you need makeup air (though probably not that much). Otherwise the duct can be blocked or removed (assuming that the "high efficiency" furnace uses outside combustion air).
Edited 12/11/2006 11:02 pm by DanH
Put an open topped box under/around it so that the bottom of the duct is below the top edges of the box, or put a "J" neck on the bottom. (The box should be sized so that the "unfilled" opening of the top of the box exceeds the area of the intake duct.)
Some jurisdictions will allow a barometric damper on it, which only opens (you'll still have some air movement) when the combustion zone pressure goes negative viz a viz the outdoor air pressure.
BTW, My understanding is that "makeup air" is air that is added to the flame itself from outside the flame but inside the furnace, and is technically different from (or is a subset of) "combustion air," but this could well be one of those areas with different usages in different areas.
The "War on Terrorism" has failed - in part by narrowing our options to only the option of last resort.
I propose we start a worldwide Partnership Against Terror, in which the reasonable people of the world work together to oppose terrorism and the conditions which lead people to that desperate condition.
"We hold these truths to be self-evident, that all people are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are life, liberty and the pursuit of happiness."
Edited 12/11/2006 11:09 pm ET by rjw
BTW, rule of thumb:
There has to be 50 cubic feet of space in the combustion zone per 1,000 aggregate BTUs of combustion appliances for there to be no need to additiojnally provide for combustion air.
If that ratio isn't met, there are various ways of adding provision, such as 1 sq in free vent space (into the rest of the house) per 1,000 btu, half near the top of the space, 1/2 near the bottom.
Sizing of the combustion duct you have also depends on aggregate BTU's, but I don't have the sizing charts at hand.
The "War on Terrorism" has failed - in part by narrowing our options to only the option of last resort.
I propose we start a worldwide Partnership Against Terror, in which the reasonable people of the world work together to oppose terrorism and the conditions which lead people to that desperate condition.
"We hold these truths to be self-evident, that all people are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are life, liberty and the pursuit of happiness."
Thanks guys,
Based on the above info, I do not think the vent is nessisary. However, I will have a HVAC guy look at it (someday!)
Erik
It takes a BIG room to meet those requirements:a 100,000 btu furnace alone needs a 20x30' room (with an 8' ceiling) to met those requirementsAnd don't forget the gas water heater (and dryer, perhaps)Nat gas water heaters are generally at least 32,000 btu, so a 100,000 furnace plus a water heater need a 20x40 roomA "typical" 2 car garage is only good for about 51,000BTU
The "War on Terrorism" has failed - in part by narrowing our options to only the option of last resort.
I propose we start a worldwide Partnership Against Terror, in which the reasonable people of the world work together to oppose terrorism and the conditions which lead people to that desperate condition.
"We hold these truths to be self-evident, that all people are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are life, liberty and the pursuit of happiness."
make-up air around here is a code requirement to get your furnace passed.
the pipe is a 4" insulated duct attached to the side of the furnace shapped like a inverted question mark or brought next to the furnace and ended in a 5 gal pail about 6" from the bottom to stop drafts , this trick seems to work well and is the one i use
under our new regulations oil tank cant be over 20 yrs old
furnace practically new with 5" vent
chimney needs 5" stainless liner or wall vent
oil line from tank to furnace entirely visible and plastic covered at time of mfg.
furnace was rated at 80.5% efficiency and they managed to get it up to 85.5% efficency