Overheated furnace room?

burleyfarm · Feb 23, 2013

My furnace room (forced air) consists of my 95% furnace and water heater, both propane. The furnace room is off my garage and is completely sealed with the exception of a makeup air vent leading from the outside. The room is about 6' by 3' and has a double door, completely sealing it off from the rest of the garage.

My problem is that I have major ice hanging from the roof in the general area of the furnace room both front and back of the garage roof. The furnace room is always very warm even when were gone for a week or two. I have 6 inches of fiberglass and another 12-15 inches of blown fiberglass over the room.

Any suggestions on how to get control over the build up of heat and ice?
I'm thinking of removing all the insulation and placing 2-3 inch rigid styrofoam between the rafters, sealing that with spray in foam for doors and windows and putting the original fiberglass back over the styrofoam. Does this make sense?

Would it cause a problem if I cut a vent hole in the top of one of the doors to let some heat out? My garage is heated so a little more heat coming into it would be great..
Thanks for your help..

Highbeam · Feb 23, 2013

So you are suspecting that the heat from the furnace room is enough to melt the snow on the roof which then runs down to the cooler parts of the roof and freezes into solid ice?

That's a lot of heat being lost to the furnace room. You aren't supposed to lose that much. FIgure you are paying for that heat that is melting the snow.

I suspect that your propane exhaust may not be making it out of the furnace room.

burleyfarm · Feb 24, 2013

Highbeam said:
So you are suspecting that the heat from the furnace room is enough to melt the snow on the roof which then runs down to the cooler parts of the roof and freezes into solid ice?

That's a lot of heat being lost to the furnace room. You aren't supposed to lose that much. FIgure you are paying for that heat that is melting the snow.

I suspect that your propane exhaust may not be making it out of the furnace room.

Yes, I suspect the heat is building up and radiating through the ceiling into the attic causing the snow melt and then freeze along the facia. There is no escape for the heat that builds up other than to radiat through the ceiling.

The furnace is 95% and uses pvc for venting. All connections are tight. The water heater is a power vent and uses pvc venting also. Both exhaust vents exit the roof and have about 3 feet of clearance.

I'm looking for the most efficient way to reinsulate the ceiling. I thought of adding 2-3 inches of rigid to the bottom of the ceiling which would be easier than rmoving all the fiberglass, but I think I'd have to add another layer of dry wall over that.

Any other thoughts?

ambenz · Feb 24, 2013

I think a return air grill added to the furnace room wall with a cheapo box fan tied to a thermostat relay to exhaust the heat from the room would be a great solution!
The more air you can circulate the better...you can really insulate but eventually, heat will rise and find a way to get into the rafters. Might as well use that heat in the garage!

kbs2244 · Feb 24, 2013

I like your door mod idea.

Socophreak · Feb 24, 2013

I would
A.Get more circulation into that room
B. Confirm that there is proper combustion taking place

p_mori7 · Feb 24, 2013

The hot pvc exhaust pipe above the cieling insulation is heating the underside of the roof. I realize it is vented thru the roof, but still a hot pipe under the roof. Does your pvc vent extend high enough ? I know you wrote 3', but how much higher is the ridge ? Is the vent capped to prevent snow clogging (don't know your location) ?

cowboyjosh · Feb 24, 2013

leaky ductwork? Did the installers foil tape or use mastic? I have witnessed un-patched holes in trunklines in furnace closets and basements; the installer makes a wrong cut into the trunk and forgets or doesn't bother to patch the bad cut. Another thought is piss poor insulation above your furnace room, if there is little or no insulation any heat no matter how little is going to cause the problems you describe.

burleyfarm · Feb 25, 2013

These are all great ideas. It's been about 5 years since the house was built. We live in northern Michigan. The furnace is a down flow.

At that time I sealed the duct with foil tape and insulated it with bubble insulation. I think I'll remove the bubble insulation and look for spots I may have missed. I'm also thinking I'll buy an insulating blanket for the water heater. I also used the bubble insulation to wrap both pvc exhaust vents where they pass through the attic. I'll also get on the roof and check out the vents for height above the roof and ridge vent although I think were good there.

I definitely will be putting in a vent so the hot air that does accumulate can escape. Not too sure if I'll need a fan for it but will keep that in mind. I think if the furnace room was in the house and not the garage, the doors would be vented and the heat would just naturaly radiat into the rest of the house.

pop pop · Feb 25, 2013

In order:
1. Check that you are getting enough make up air for combusion - install a CO meter/alarm in the room. Mofify something to get enough air into the room.
2. Insulate the HW heater with a blanket.
3. Your high eff. propane will have a LOT of water vapor in the exhaust that condenses when it hits outside//cold air. It's raining on your roof. That runs down the roof till it cools enough to freeze.

no. 205 · Feb 25, 2013

I agree with "pop pop". Very good advice.

sands35 · Feb 26, 2013

In three houses that I've owned in 5 years.... ALL needed to have duct work taped. Each time I did it, it dropped the local ambient temperature down ~10*F or more.

DPelletier · Feb 26, 2013

OK,

I assume that your water heater is natural draft since you have a combustion air duct into the space? ...is this a combustion air duct or a fresh air duct? CA normally terminates 18" above the floor, a fresh air duct would be connected to the furnace return air duct.

normally I would suggest more insulation and an exhaust fan discharging into the garage hooked to a reverse acting thermostat which would draw outdoor air into the furnace room through a louver or hood with a back draft damper but you shouldn't induce a negative pressure into a mechanical room with naturally vented gas fired equipment (the furnace should be sealed combustion, drawing combustion air directly from the outside).

Your PVC venting shouldn't get very hot; if it does, something is wrong. Your heat could be from duct leakage or it could simply be radiating from the equipment. Insulating the DHWT is a good idea.

Dave

burleyfarm · Feb 26, 2013

The air duct into the room is for the water heater combustion air. It was originally installed leading down from the attic. This was great for introducing air but it let all the hot air from the furnace room into the attic. I removed it, sealed the hole and installed a new make up air from the outside.

The furnace return duct is connected to a fresh air makeup which is separate. The combustion air for the furnace is a separate pvc vented directly into the furnace. The furnace exhaust vent has a drain for condensation that drains directly into a condensate pump where it is pumped to waste. I don't think the moisture is from the exhaust but I'll get on the roof tomorrow anyway and check.

My furnace doesn't run much since this house has been our vacation home and was only getting used about twice a month. When not there we keep the themostat at 60 and turn the hot water heater off. When we have been there we use our pellet stove as much as possible.

I did conduct a quick check of the furnace for leaks when I arrived home this evening. I found that I didn't seal the back of the furnace where it connects to the hot air plenum. Not sure what to do about it as there is no way to get back there to seal it. I can just reach the nearest back corner with my finger tips and I'm no where near the far corner or back side.

brewchief · Feb 26, 2013

Duct mastic is the best way to seal up the ductwork, much better then tape.
Got a pic or two of the furnace room? I might be able to come up with an idea or two to seal it up if I see it.

burleyfarm · Feb 28, 2013

brewchief said:
Duct mastic is the best way to seal up the ductwork, much better then tape.
Got a pic or two of the furnace room? I might be able to come up with an idea or two to seal it up if I see it.

I'll take a picture asap and post it. My camera battery is dead and we are in the process of moving and can't find the charger.

thanks all for the ideas.

DPelletier · Feb 28, 2013

burleyfarm said:
The air duct into the room is for the water heater combustion air. It was originally installed leading down from the attic. This was great for introducing air but it let all the hot air from the furnace room into the attic. I removed it, sealed the hole and installed a new make up air from the outside.

The furnace return duct is connected to a fresh air makeup which is separate. The combustion air for the furnace is a separate pvc vented directly into the furnace. The furnace exhaust vent has a drain for condensation that drains directly into a condensate pump where it is pumped to waste. I don't think the moisture is from the exhaust but I'll get on the roof tomorrow anyway and check.

My furnace doesn't run much since this house has been our vacation home and was only getting used about twice a month. When not there we keep the themostat at 60 and turn the hot water heater off. When we have been there we use our pellet stove as much as possible.

I did conduct a quick check of the furnace for leaks when I arrived home this evening. I found that I didn't seal the back of the furnace where it connects to the hot air plenum. Not sure what to do about it as there is no way to get back there to seal it. I can just reach the nearest back corner with my finger tips and I'm no where near the far corner or back side.

OK, it all sounds right then. Do NOT exhaust air from the furnace room or you could cause improper venting of your water heater.

- Seal the ductwork
- insulated the HWT
- add insulation to the attic if possible.

as far as sealing the ductwork goes, do not use duct tape as it doesn't work. Low velocity duct sealer is what I would normally recommend, but where you have difficulty reaching, use a fibre reinforced foil tape. This tape is regularly used for HVAC insulation and should be locally available. If you just need a bit, try your local HVAC/Sheet Metal Contractor and you might be able to get a small pce for little to nothing. There is an even better product that is a tape with mastic on it but it's harder to install and even harder to find.

Dave

DPelletier · Feb 28, 2013

I re-read your post and realize that even the tape might be impossible to install. If that's the case, all I can think of is either: a) cutting an access into the plenum and sealing it from the inside or b) take it apart and install a gasket on the joint.

Dave

burleyfarm · Feb 28, 2013

DPelletier said:
I re-read your post and realize that even the tape might be impossible to install. If that's the case, all I can think of is either: a) cutting an access into the plenum and sealing it from the inside or b) take it apart and install a gasket on the joint.

Dave

Your giving me some good ideas Dave. I used a metal tape made by Nashua on the joints I could reach on the furnace. On all the other duct joints I used a brush on fiber sealer. Don't remember the term for it.

I noticed the installer used a clear sealant on the front and two sides where the AC box, plenum and furnace meet. Too bad he didn't seal the back before he connected the rest of the duct. I think I'll attempt to remove the main duct to gain access to the back of the furnace, then reinstall and reseal it. I'm thinking I'll still need to add some additional insulation to the ceiling.

Overheated furnace room?

burleyfarm

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Highbeam

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burleyfarm

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ambenz

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kbs2244

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Socophreak

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p_mori7

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cowboyjosh

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burleyfarm

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pop pop

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no. 205

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sands35

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DPelletier

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burleyfarm

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brewchief

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burleyfarm

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DPelletier

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