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Old 08-18-2011, 10:52 AM   #1
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Furnace venting plan - comments?


I am still looking at venting options for replacing the old 80% gas furnace with a new 95+% unit in my towhhouse. Old unit uses type B vent out the roof shared with water heater so that won't work.

I have sketched out a plan to run the PVC direct vent and intake pipes that I think will work and meets code. I have attached a picture. Anyone have any comments?
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Old 08-18-2011, 01:35 PM   #2
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Furnace venting plan - comments?


would be better if you posted some actual pictures of that area.

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Old 08-18-2011, 05:07 PM   #3
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Furnace venting plan - comments?


Here are a couple of pics.

Pipes would leave the util room through this joist bay.



Pipes would go through the void space under the stoop and make a 90 degree right turn and exit roughly where the paper is taped to mark about where the bay vent would go.

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Old 08-18-2011, 06:52 PM   #4
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Furnace venting plan - comments?


Looks like a good location. No issues with common walk ways,window,doors,gas or electric meters being too close so the inspector should not have any problems with it.
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Old 08-18-2011, 07:06 PM   #5
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Furnace venting plan - comments?


if it gets cold under that space then the exhaust will need to be well insulated and also it needs to slope back to the furnace otherwise it should work OK.
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Old 08-18-2011, 07:44 PM   #6
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Furnace venting plan - comments?


Yes, it is located so the pipes will slope back towards the furnace by the required amount. Also, that void space is definitely unconditioned. It is attached to my house so probably retains some heat but it likely gets below freezing on really cold days. What kind of insulation would work? That black foam pipe wrap? Or is there something more compact that would do the job? Yuri, you mentioned some sort of refrig tape in the other thread.

It will be a PITA to pull the bricks, run the pipes, and refinish the vent outlet area. But that is really my only alternative. And there is no telling what is in the void. Probably dirt and construction debris. I'll probably drill a hole from the inside this weekend and have a look with a borescope.

Thanks for the feedback, guys.
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Old 08-18-2011, 07:58 PM   #7
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Furnace venting plan - comments?


we have the same type of insulation that is used on the outside of AC lines and in the trade it can be called "Armaflex". we can get it in 2" or larger but I don't know where a DIYer can find it. it needs to be sealed/insulated perfectly as the water that is in it will eventually hit a cold spot and freeze and get bigger and bigger and block the pipe even though most of it drains back the inside of that pipe is always moist. you will always have drafts thru bricks so that area is going to be cold. maybe some of the other guys have some ideas but my co. uses that refrig armaflex stuff. Google it and there is info out there 4U.
http://www.a-f-insulation.com/docume...ipe-Insulation
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Old 08-18-2011, 08:32 PM   #8
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Furnace venting plan - comments?


That space actually butts up to houses on 2 sides, mine and my neighbor's so that should moderate the temps a bit. Not sure of the brand but the big box stores sell split black pipe wrap which probably should work with some tape. Also, I have a friend of a friend in the commercial HVAC business I can ask and perhaps get a source or even some remnants from a job. I'll need only about 6 feet. And I am not in a hurry... still trying to decide if I really want to replace a working but old system for improvements in comfort and efficiency... and to minimize the chance for failure at a bad time.


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we have the same type of insulation that is used on the outside of AC lines and in the trade it can be called "Armaflex". we can get it in 2" or larger but I don't know where a DIYer can find it. it needs to be sealed/insulated perfectly as the water that is in it will eventually hit a cold spot and freeze and get bigger and bigger and block the pipe even though most of it drains back the inside of that pipe is always moist. you will always have drafts thru bricks so that area is going to be cold. maybe some of the other guys have some ideas but my co. uses that refrig armaflex stuff. Google it and there is info out there 4U.
http://www.a-f-insulation.com/docume...ipe-Insulation
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Old 08-18-2011, 08:43 PM   #9
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Furnace venting plan - comments?


These guys have it. Looks like the size for 2 1/2" copper would be the best fit for 2" PVC which is about 2 3/8" OD. Wouls also need to cut up a piece or get some Armaflex sheet to do the elbows.... or maybe I'll cut up an old wetsuit I have laying around.

http://www.statesupply.com/maintenan...rmaflex-ig1040

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Old 08-18-2011, 08:44 PM   #10
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if that is the only place to vent it then you do want to do it B4 the furnace dies and you have a panic situation. going to be a time consuming job and most contractors don't want to start busting bricks and doing jobs like that as we get blamed for cosmetic damage. may be very hard to find someone to do it in a hurry or at all.
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Old 08-18-2011, 09:02 PM   #11
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Furnace venting plan - comments?


Agreed. And yes, that is the only place for a Cat 4 vent. The rear option turned out to be impossible because of the 25' span through finished space (so would have to be above ceiling drywall) and because of the pitch requirement that would make it terminate too close underneath the 2nd floor deck. I hoped that path would work but detailed measurments put that to rest.

The fallback if in a hurry would be to just drop in another 80% er. I am pretty confident I could repair the one I have if it failed and if I could get the parts like circuit boards and blowers... but I'd rather not have to put $$ into a 16 year old system. But it is in good shape. I was in there cleaning the evap coil (it was really clean already, BTW) and the furnace HX looked brand new. The other beauty of being an inner unit TH is that the neighbors add a lot of insulation on the side walls. That would make all but the most extreme conditions tolerable for awhile w/o risking freeze damage.


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if that is the only place to vent it then you do want to do it B4 the furnace dies and you have a panic situation. going to be a time consuming job and most contractors don't want to start busting bricks and doing jobs like that as we get blamed for cosmetic damage. may be very hard to find someone to do it in a hurry or at all.
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Old 08-18-2011, 09:09 PM   #12
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Furnace venting plan - comments?


well at least you have a viable plan now.
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Old 08-19-2011, 06:31 AM   #13
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Furnace venting plan - comments?


If you live in a Condo you may want to check with the board. Some of them won't allow changes to the outside of the bldg/sightlines etc.
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Old 08-19-2011, 07:15 AM   #14
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Furnace venting plan - comments?


It's a townhouse, but yes we have a Home Owners Assoc and architectural code. I don't see anything in it that would be invoked for such a trivial change. I did call them before I installed the hose reel back in 1996 and it was not an issue. This will be less intrusive than that. But I think I'd try to find a way to paint the bay vent to blend in a bit... maybe even glue on some of that brick print vinyl or wall paper.
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Old 08-19-2011, 01:14 PM   #15
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I would get confirmation from them. there will be smoke/white vapor shooting out and some malcontent neighbor may not like the look of that. some people just like to be miserable and complain. pretty hard to undo the work if they complain later. we always get the homeowner to check before doing any condo work.

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