Venting High Efficiency Furnace
user-773
| Posted in Energy, Heating & Insulation on
I am about to purchase a new house with a high efficiency furnace fueled with propane. The vent and fresh air intake pipes are PVC protruding from a side wall to the outside. The vent pipe is about 10 inches long and 15 inches above the ground, sticking straight out from the wall with nothing capping it. The fresh air intake pipe is an elbow with the opening facing the ground. The end, with the opening, is about 10 inches above the ground. My concern is that both ends have nothing on them to prevent critters or debris from entering. Also, what happens when we get a substantial snowfall and theses two things are buried.
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Try posting your question at http://hvac-talk.com/vbb/forumdisplay.php?forumid=1
Some good heating and A/C experts over there.
They do have screens available for these things. Try a plumbing supply house.
The snow is a real problem with side-vent. You have to keep it shoveled. Nearby, there were deaths when a power-vent was blocked by snow this past winter. The death part should not happen with your sealed unit though. Would just shutdown.
My concentric vent is about 18" above the ground and I have never had a problem in the north woods of Illinois. Lots of critters and 3-4 feet of snow each winter. The exhaust will melt what little snow might block it. When heavy snows occur, have look and clear away as necessary. You generally don't have to worry about debris but do not put a screen across these pipes. The furnace will not operate if the air flow though the combustion section does not meet minimum requirements. If it does fire some time, check and see if there is a clog, otherwise, don't worry.
I installed one of these in my home last year. The instructions were clear. The intake and exhaust must be installed at least 18 inches (I think) higher than the highest snowfall that can be expected. I installed accordingly, but I notice many installations in my area are way too low. I haven't heard of any related deaths or fires locally though. I work as a paramedic in our local fire department and regularly see problems with boilers causing or nearly causing fires or CO2 problems. In all cases that I've seen they have been older traditional boilers that don't have sealed combustion. Whether the installation was perfect or not having a sealed combustion type unit like yours probably puts you way ahead in the game.
Most (not all) call for 18" above grade or above the highest anticipated snow level.
Few are installed that way. Few have problems, so far as i know.
If the flue is blocked, the pressure switches are supposed to shut it down,
So far as I know, none have pressure switches on the intake side.
definetly check the manual, the vent should have an elbow, I too worry about a mouse crawling up the pipe but any kind of screen could become a source for ice build up from condensation in the exhaust ... dammed if you do ...
>>definetly check the manual, the vent should have an elbow,I don't know of any that require an elbow on the vent - because they are designed to handle condensate in the flue gases, they can handle rain water as well. (The air intake needs an elbow, though.)And, forwhatever reason, wildlife in the vent or air intake doesn't seem to be a problem that the HVAC folks I know have experienced.
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Sojourners: Christians for Justice and Peace
I just checked the Carrier site, could only find operating manuals, but the installation manual definitely prescribes an elbow, even if it is not "really" necessary, if something goes wrong and it isn't installed as per the manual your SOL, so .. ps know of one unit that froze up and blocked because of a fur ball ..
It sounds like a lennox setup. OP needs to give a make and model.
yup, the other reason they like to put an elbow on it is to disperse the vapour away from the house, away from the house and soffit ..
I'm not sure if soffit clearance is an issue, since he's worried about being too close to the ground.Something very important which hasn't been mentioned yet is that the flue and air intake have to be well separated (typically, the flue has to be above the air intake.)Otherwise, the air intake can start pulling flue gases which results in huge carbon monxide problems (from lack of oxygen in the combustion air*), poor furnace efficiency and, in really cold weather, the air intake can get iced up.-----------
*FWIW, oxygen content in air runs about 20-21%, in 90+ flue gases it's tyipically down to about 9-10.5%
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Sojourners: Christians for Justice and Peace
Bob, start watching exhaust patterns in the winter. I know of a couple of situations where it is a problem.
YEah - I've got a great shot of an iced up air intake, but it is MIA on the hard drive
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Sojourners: Christians for Justice and Peace
It was a long day. What I meant was watch for exhuast being drawn into soffits.Especially if there are whirlybirds on the roof.
Are you thinking of through-roof mounting?Or perhaps through wall up near the soffits?I've never seen them mounted high on a wall, but suspect that is a regional thing.
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Sojourners: Christians for Justice and Peace
10' below the soffit, but on a calm day the exhaust drifts up and the attic is in a negative pressure so the exhaust gets sucked right in through the soffits. Really is interesting to see.
Interesting - I'll have to keep my eyes open for that.Thx
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Sojourners: Christians for Justice and Peace