6 inch furnace vent. Can I use two elbows in place of a real cap?

Submitted by Scozz554 t3_y6ibtx in DIY

Basically the title. I discovered our furnace vent cap blew away when I found water dripping on my basement floor at the bottom of the riser.

Climbed up and checked and it appears to have about a 6 1/2 inch ID. I am guessing this is a "6 inch" duct. I am having a really hard time finding a 6 inch [or larger] vent cap without shelling out an unreasonable amount on Amazon. So question is:

Can I just, even temporarily [few months, til I feel like getting on the roof again], fit two elbows into a u and fix them to the outlet to keep water out for now?

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statikuz t1_ispumoj wrote

What's your definition of an unreasonable amount?

https://www.homedepot.com/p/Master-Flow-5-in-to-7-in-Adjustable-Versa-Cap-5070/100396919

https://www.menards.com/main/heating-cooling/venting/b-vent/amerivent-reg-b-vent-cap/6ecw/p-1444432082385-c-9462.htm

https://www.plumbersstock.com/duravent-0133-6gvvth-6in-vent-top-type-b.html

It could be a code enforced thing so insert all the usual "you should ask someone" stuff.

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Scozz554 OP t1_ispwtbu wrote

Yeah I imagined a u would be not code, but it could keep things dry until I got a proper one up. Nothing is available locally and things are expected to be wet and below freezing in the next few days. I can find 5" all day. I could reduce to it but that feels more wrong than my u-vent.

Just trying to get something up before I'm no longer willing to be on my roof.

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thblackdeth t1_isqig14 wrote

If it's just capped off (no flow) there is no functional difference between reduced or not. Diameter is to allow more airflow

Edit: misread the post, I saw cap, not vent cap. Disregard

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statikuz t1_isr3bp6 wrote

> If it's just capped off (no flow)

Wait, nobody is talking about literally capping it off...

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Scozz554 OP t1_issy8pg wrote

Dear reddit. What's the best way to plug up my furnace exhaust for the winter? I'd like to spend less on my heating bill.

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Fawxhox t1_isq01vh wrote

Assuming you don't care about code and it's temporary, I would just get a piece of scrap metal and make one. Use tin snips or something to cut a circle about 10 inches in diameter, put a few legs on it and mount it on top of the pipe. I'd worry about flow bring cut down with two elbows. I mean it'd probably be fine but just in case. If it's a wood furnace I'd also worry about soot build causing a fire.

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Diligent_Nature t1_issrhbl wrote

Are you sure the water didn't enter on the outside of the pipe? You also need to screen it to keep critters from getting in there. Don't use two elbows get a proper cap.

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rededelk t1_isssetj wrote

Do it right. My neighbors went south for the winter and after 8 feet of snow their oil heater was clogged and cost them $50k restoration, house was covered in soot

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Reelfungi t1_isvs290 wrote

You can’t put a gooseneck on a flue like that. You need vertical flow to maintain draft. Just go to a plumbing supply house and ask for a rain cap. It shouldn’t be that expensive

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usedTP t1_ispqoex wrote

Get a professional to fix it. Carbon Monoxide should not be trifled with.

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