Furnace Roof Vent Ice Dam and Resuilting Roof Leak - HELP!!!

HVAC_Rookie

Hello folks - I'm really hoping someone can help me with this problem I've been trying to solve since last winter. As you can see I from the pictures I had a vertical ice damn being formed by the furnace roof exhaust vent. First I thought it was a roof problem but the roofer of the recently installed roof rightfully pointed out that there is no water leaking even after the heaviest rain. And then we saw theses vertical ice dams. Problem seems to be that none of the HVAC people I've spoken to seem to know how to address this. Two claim its a roof problem, while the last one side I should saw off the exhaust vent so that it is vertical pointing upwards which he feels means there will be nothing dripping out of it and thus no ice dam accumulation... ANY THOUGHTS PLEASE??

Zman

What model equipment is that venting.
Straight up is a good idea provided the manufacture approves.

HVAC_Rookie

Zman thanks for the comment.. it is a Comfortmaker furnace - can't seem to find anything that looks like a model name or number.

Zman

I would cut it off and go straight up, just like in the manual. https://www.utcccs-cdn.com/hvac/docs/1011/Public/0C/44001201003_ICP_5970.pdf

DZoro

The exhaust should go straight up, keep elbow on the intake. They should be a minimum of 18" apart.

Jamie Hall

Go straight up. If you are concerned about the possibility of rain getting into the pipe -- which is a very minor problem and one I wouldn't worry about (the top cap on chimneys for fireplaces which you often see is there to keep the birds out, not the rain) -- you can put a lid over the top opening -- a flattish cone (tip up!) about twice the diameter of the pipe and set the diameter of the pipe above the top of the pipe. If that makes any sense.

Leonard

Looks to me like it's an ice stalactite. Formed either by dripping water or cold steam vapor condensing on roof.

Just curious, have you ever seen it grow so tall it meets the pipe?

If I didn't have the installation manual I might have installed a Tee fitting on the vertical pipe ( as they like to do in England)

captainco

It should be straight up. I don't believe a flue should ever be 180 degrees back down. Rain is good because it helps neutralize the condensate in the furnace. Birds can get in any vent pipe. Can't cover them or they will freeze shut.

HVAC_Rookie

Guys thanks very much for all of the great comments. I took the advice and had the vent cut so that it goes straight up. However as you can see now there is ice somehow accumulating along the based of the vent/flashing. Any ideas on what can now be causing this?? Could the cap somehow be causing the problem??
Thanks in advance for any help!

KC_Jones

It looks like they put a cap on it, I am pretty sure that isn't necessary and probably causing the issue.

Harold

My two cents. If the new roof is properly installed and the two pipes properly installed with appropriate materials at the base; the ice should not matter. I would guess it is possible for melt and remelt could affect the roofing. But it should not cause damage.

I have a question: should the exhaust pipe be below the intake? Or does it matter. It would seem to me that in the new configuration the intake would inhale some of the exhaust.

DZoro

That's wrong, should not be a cap on it, it should be higher than the intake pipe, and at least 18" away from the intake pipe. That ice will push up on the shingles and find its way in. Keep the exhaust pipe straight up no tee's , 90's, caps.

HVAC_Rookie

Guys so is the cap a problem because air going up is being forced back down to the roof and then freezing?
Thanks.

SuperJ

HVAC_Rookie said:

Guys so is the cap a problem because air going up is being forced back down to the roof and then freezing?
Thanks.

It's a problem, because the moisture in the flue gases (steam) hits the cold cap, condenses, and then drips down and freezes on your roof. Without a cap any condensation will flow back down the vent pipe and be dealt with thru the condensate drain at the bottom.

DZoro

Don't forget that that condensate is VERY CORROSIVE. Not something you want running down your roof, gutters, siding....

NeverDone

Point the exhaust straight up, no cap. Its done like that here in WI all the time. The cap is the cause of the condensate dripping.

NeverDone

Also it might be a good idea to put a reducer on the end of the pipe to drop 1 size, for example 1-1/2 -to- 1-1/4. Lennox calls this an 'accelerator' and it increases velocity to help blow the exhaust further away from the termination point to prevent exhaust from being drawn into the intake.

John Mills_5

Yup, blow straight up. There's a drain in the furnace if a little bit of rain gets in it. I see these elbowed over all the time. Like DZoro said, you don't want that stuff on your roof. I have a picture somewhere of one that blew on an adjoining chimney and the mortar is totally gone between the bricks.

HomerJSmith

A permanent solution would be to not use your boiler in the winter time.

Ya, saw off the coupling at the pipe and glue a new coupling on the exhaust pipe. You could also glue a vertical facing pvc vane in the top of the coupling that would help with down drafting.

In case you're wondering, the exhaust vent is the one with the ice stalagmite.

TonKa

NeverDone said:

Also it might be a good idea to put a reducer on the end of the pipe to drop 1 size, for example 1-1/2 -to- 1-1/4. Lennox calls this an 'accelerator' and it increases velocity to help blow the exhaust further away from the termination point to prevent exhaust from being drawn into the intake.

Do not do this without consulting the installation manual for the exact make and model of your furnace. Don't do it if it is not in the manual.

hot_rod

The flashing should seal any water from getting inside, is it in good condition? The rubber seal tight and flexible?

In snow country we would run those vents up near the ridge, to prevent damming, which often lead to shearing off of the pipes. Assuming the vent tables and fittings
fell within the max. Length tables

ethicalpaul

Sorry but this notion of poor roof insulation is wrong or misguided. Unless the attic is finished, you don't want any "roof insulation". You want the attic to be cold, so it would be expected that the roof would be cold and water on it would freeze.

And even if the attic is finished, the rooftop itself should be cold due to the insulation between the conditioned space and the outdoors.

You want a lot of snow on your roof.

Brent H.

Bear in mind that this is a 4 year old thread but it’s still interesting reading.

ethicalpaul

Well it WAS a 4 year old thread LOL