combustion air intake

[Tom7227]

I have a 5 or 6 inch duct that is providing combustion air to the furnace. An awful lot of cold air is coming in and cooling off the basement. I elevated the end of the duct about 4 feet and that may be a bit of a help but it still seems like something could be done to only have the air flowing in when the unit is fired up. Any ideas on how to deal with this, or is that just the way it is?

Thanks for your time.

Tom

[soldoncass]

They are supposed to have a bend (like a horseshoe)at the bottom....does yours have that? I have heard about people putting the horseshoe end in a 5 gallon bucket, that may help. Just make SURE it stays OPEN, or there could be big problems with backdrafting...(carcon monoxide being sucked back down the chimney)....definitely NOT healthy.

Is the outlet end of your intake pipe on the windy side of the house?

[Redlantern]

I agree with SoldonCass. Either a bend in it so it looks similar to a P- trap or stick it in a five gallon bucket, making sure it's not touching the bottom of the bucket. This helps keep the cold air from spilling out onto the floor. I've seen the cold air spill out and freeze a water service before because there wasn't a trap in the fresh air intake. Doesn't normally happen but it was extremely cold weather.

[Tom7227]

I've got a J but I'll move down the alphabet and try a P. I doubt that it's long enough for both a P and a bucket.

Thanks guys.

Tom

[chad austin]

Tom,

The bucket works better in my opinion. When I bought my current house I had your same issue. So I took out the "J" and cut the pipe just short of floor height and stuck it in a bucket. Much better!

[Tom7227]

I was getting ready to make some changes when I realized that I have replaced the furnace that was the reason why it was installed with a high efficiency rig that has a combustion air intake in PVC all it's own. Maybe I don't need this tube thing afterall. All that's left is a power vent water heater and the gas dryer that have exhaust. What about this?

[MNice]

Still need it, power vent water heater & gas dryer burns indoor air.

[soldoncass]

The efficent, sealed combustion furnace won't need it....the efficent sealed water heater won't need it, but, the cold air intake size is based on the TOTAL of ALL exhausts (such as bath fans, gas dryer, vented microwave, fireplace, etc.). When you have any fans/vents blowing inside air OUT, there has to be an equal volume of outside air coming IN(through an fresh air intake pipe)...or the negative pressure will draw in air from somewhere. Common places are downdrafting appliances , doors and windows leaking, etc. I don't know how tight your house is built, but the newer ,tighter ones need enough fresh air to completely change the air inside every so often (I don't remember frequency), just to keep good oxygenated air for breathing ,etc. Your gas dryer needs oxygen to burn efficently, just as much as YOU NEED it to breath. I hope this helps some, but there are many variables, but do you Need fresh air in your house, and a fresh air insulated pipe is the best way to do that.

[WallEYES]

SOLONCASS??????? The power vented water heater still needs combustion air.... any exhausted appliance such as bath fans and kitchen exhaust need make up air which is different than combustion air. If your house was built before before 2000 and the basement is unfinished or your CAS(combustion air space) of which your mechanical equipment sits...odds are you don't need any combustion air. Air exchangers ventilate the house...better air quality...exhausts and brings in equal air at maybe 3 air changes per hour. I have a six inch combustion air in the house and installed a motorized damper on it and interlocked with my furnace. The damper stays closed until the furnace kicks on supplying combustion/dillusion air to the space. very cheap to do

[soldoncass]

Walleyes,

Interesting idea about the damper tied into your furnace. I've never seen or heard of that method. That would be a neat thing to do IF your furnace was older(not closed combustion), and you have an electric water heater. I've seen houses that the owner didn't like the COLD AIR coming in the pipe....so they plugged the pipe. That caused backdrafting, down the chimney, and boy did that make a mess. For that reason I will never tell anyone they don't NEED the pipe anymore.

As far as the air exchanger being the best for changing house air....I agree, but there are MANY older houses that only have exhaust fans venting bathrooms, they still need fresh air coming in that equals the total outputs.

Tom, Please get a professional to look at your situation before taking the pipe out....they can give you option, ideas, costs before you decide what is best for your house.

[Tom7227]

I had an energy audit since I first posted this and it included a blower door test. The energy audit report has a graph showing the amount of air leaks showed the house in what I will label as the 75% category - that's on the bad end. Since that report I have done everything recommended on the report. Obviously this has sealed up the house but it's till a 50 year old house.

The intake pipe is causing the basement to be at least 10 degrees colder. I don't have much heat going down there. The attached garage door opens right near the intake vent and some air can come that way. I am having a tough time rationalizing keeping that pipe going with that heat loss. The guys that put in the furnace put it in and plugged the old one that only had a short 3 inch pipe on it. If a 3 inch opening was enough why would I need a 5 or 6 inch one for adding a high efficiency furnace that has it's own combustion air intake?

[Surface Tension]

Do the bucket or P and see if you have less air piling in.

I stayed at a resort and the cabin we were in lost heat from the furnace.

We did have a gas fireplace that up till the cold front moved must have been enough to the the place.

It was probably -10 plus high winds.

This was a big place, a louvered door indicated that was the place that housed the furnace.

It was a very small utility room containing a high efficacy(condensing)direct vent furnace, water heater, and 6" combustion air duct. Cold air was blowing in from the 6" duct on account of the inlet was on the side of the building the wind blowing into. Result, it was freezing in there.

The 2" intake for the furnace was on the same side of the building.

The furnace's trap and the line from inducer to switch were frozen.

Everything was as it should be but there has to be a better way.

[shizzy]

I do the bucket thing in my 83 year old house. it works quite well. you want to get the bottom of the tube as far down in the bucket as possible without it sitting on the bottom for maximum effect.

In my basement it's worth an easy 5-8 degrees of increased basement temp.