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Old 01-30-2011, 07:06 PM   #1
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Did I create an intake problem?


I built this deck this past summer. My furnace is a 90 plus I guess? has an intake and exhaust in one pipe assembly. When I built the deck, the ledger board on the house had to be exactly in line with the intake/exhaust. So I broke the ledger just before it and started back just after it (see attached photo). Anyway, the furnace started the past fall and seemed okay at first. But then it started with a code flashing code 34. A friend of mine is a HVAC guy, but I hate to call him every time I have a problem of any kind. We lived across the street from each other for 14 years and are good friends. However since I moved were live about 15 miles apart and it seems like the only time I call is when I need something. Back to the issue, he and I ran thru this on the phone and he had me check a bunch of stuff and none of it was wrong. Finally I loosened the cover on what I call the fire box and it ran as it was supposed to. I look at the intake outside and nothing was in the openings but it was about 1/2 from the house. He thought it was too close and suggested if there was room, move it out to about 3 inches or so. I did that and at first it helped, but a couple days later it was back to it's old tricks. I finally got po'd and took a hole saw and made one 1.5 inch opening in the intake about a foot up next to the furnace and it's worked fine since. BUT, as I am finishing my basement and closing that area off from the rest of the basement, I feel I need to get to the bottom of this. I hope you can see in the photo where I build the deck around the intake. Is it possible I have restricted the air flow to the intake? Thanks and sorry for the long post.


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Old 01-30-2011, 07:30 PM   #2
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Did I create an intake problem?


Yes, and you have created a worse problem with the exhaust recirculating into the intake. This will corrode the heck out of your burners etc and cause it to burn badly and foul up the heat exchanger and do serious damage. You have what is called a concentric kit. I would suggest you re-vent the furnace out a different wall. Your furnace (carrier/payne/bryant is it?) is not approved for taking air from inside the house nor is it legal to sell the house and leave it that way. Sorry.

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Old 01-30-2011, 07:49 PM   #3
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Did I create an intake problem?


Thank you for that. It is a Bryant. The previous owner had added a 90 elbow on the exhaust portion. Could I extend that farther away? Is the exhaust being drawn in what is causing it to think it is being starved for air? Quality of air vs. volume?
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Old 01-30-2011, 08:32 PM   #4
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Did I create an intake problem?


I have worked on hundreds of them (used to sell them). They can be VERY finicky if they don't get 100% clean air. Gas burners won't tolerate a lack of oxygen from recirculated exhaust gas and the moisture in it is very bad. That furnace is VERY sensitive to being vented EXACTLY according to Bryants specs so no I would not alter the venting. Will develop nuisance pressure switch tripping and can affect the way the burner lights etc etc. They put a lot of testing and engineering into that concentric kit so it works properly in an open area. You can re-vent it with a 2 pipe setup and gooseneck it above your deck but it will be UGLY. No easy solution unfortunately.
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Old 01-30-2011, 08:53 PM   #5
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Did I create an intake problem?


Well, it looks like I will be doing some deck remodeling. What is the minimum space around the vent/intake assy?
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Old 01-30-2011, 09:02 PM   #6
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Did I create an intake problem?


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well, it looks like i will be doing some deck remodeling. What is the minimum space around the vent/intake assy?
the code/manufacture requirements for the venting of your bryant/carrier furnace ,requires you to extend the venting beyond the deck.your termination you refer too is called a concentric.check with the installation instructions to be sure you are not exceeding any lengths,and amount of turns that apply to your furnace .usually minus 5 feet per 90,2.5 per 45 good luck im sure youll be fine
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Old 01-30-2011, 09:08 PM   #7
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Did I create an intake problem?


Another thing to know is that the intake and exhaust should be within 1 foot from eachother to prevent cross draft in the burner compartment.2 inch pipe is not necessarily the right size,it depends on the btu of your furnace ,hence refering to the installation manual.also be sure the intake is at least 12 inches above anticipated snow level,here in va that would be 6 inches ,plus 12 .good luck.......ONE OTHER THING YOU SHOULD KNOW ....extending the pipes beyond your deck will also require them to be insulated ,to prevent freezing of the condensation in the pipe

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Old 01-30-2011, 09:10 PM   #8
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Did I create an intake problem?


I hate to say it but it really is designed to be used on an open flat wall. I would want at least 3 feet as the exhaust comes out at a fair velocity and anything less will bounce back and get sucked in. Still may recirculate in no wind conditions even with that clearance. It is amazing how little an amount of exhaust back into the intake will cause burner problems and will eventually cause your secondary heat exchanger to plug up, overheat and they will void the warranty if it is overheated. You can replace the furnace with a brand/model that is approved for single pipe venting and gooseneck it above the deck(Lennox G61V is a good candidate) One pipe won't look ugly, 2 will. How old is it. If it is close to 15 yrs I would think about it. I'm back tomorrow.
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Old 01-30-2011, 10:12 PM   #9
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Did I create an intake problem?


I looked and this is a 340MAV direct vent unit. I'm trying to come up with a solution to the deck vs. concentric situation. Would it be possible to remove the concentric and extend the two 3 inch pipes outside the house wall, turn them down with 45's below the joist of the deck and then 45 again and then run them out from under the deck? They would both be at least 30 inches above grade. Ideas welcome.
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Old 01-31-2011, 02:53 AM   #10
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Did I create an intake problem?


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Originally Posted by MikeKy55 View Post
I looked and this is a 340MAV direct vent unit. I'm trying to come up with a solution to the deck vs. concentric situation. Would it be possible to remove the concentric and extend the two 3 inch pipes outside the house wall, turn them down with 45's below the joist of the deck and then 45 again and then run them out from under the deck? They would both be at least 30 inches above grade. Ideas welcome.
Bummer man. Not trying to be a turd but how could you not realize the that little teeny space wouldn't work? No you cant have any dips in the PVC, it has to have 1/4" per foot of rise all the way. My first reccomendation would be to hire a quality contractor to come out and go over solutions with you, cost you a few hundred bucks. You may want to look into using the old metal furnace vent thats likely capped off provided your water heater isn't vented into it. Those 5" B vent pipes can fit 2 2" PVC pipes or 1 3" pipe. They have to be run all the way up with a 90 on the intake. As for the roof cap you have have to get some snips and bumble about. Not sure where the furnace is located and if the PVC pipes are accessible. Another crappy idea is to run them up through the deck against the house and up through the overhang with a roof termination. Its ugly as sin but its still done from time to time.
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Old 01-31-2011, 02:56 AM   #11
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Did I create an intake problem?


Oh yeah and you prolly wont have nearly enough rise to go to the end of the deck, plus that deck is awesome. Who would want pipes comin out of it?
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Old 01-31-2011, 05:39 AM   #12
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Did I create an intake problem?


Good advice and correct. No dips allowed and it needs to be completey insulated on the exhaust pipe so it does not freeze and sloped back to the furnace. There is also a maximum allowable length of pipe run which has to have elbows (equivalent length per elbow) added to it. Too long and it trips the pressure switch. Sorry.
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Old 01-31-2011, 07:36 AM   #13
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Did I create an intake problem?


Well, lots of good info here for sure. At this point the lessor of the evils in my mind is to remove the concentric, replace it with separate intake and vent pipes thru the wall and bring the ends up thru the deck there. The furnace is located directly below the kitchen dead center, so thats not an attractive option. I wouldn't have room for the necessary elevation going out even if I could drop below the deck joist (which it appears I can't). The joist run parallel to the house, so I couldn't go that way even if the rise wasn't needed.
It never occurred to me that the concentric was that picky. I should have checked into that prior to building the deck. But I would have been doing something like this then, because the deck had to built as it is.

Quick question, is PVC PVC? or is this a special type?

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Old 01-31-2011, 06:32 PM   #14
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Did I create an intake problem?


In Canada we have to use approved 636 grade PVC which is a higher grade than your average PVC. Depends on what your local gas codes allow and gas inspector allows. Best to find out for sure as you could be liable down the road if you sell the house and your setup is not to code. Here is an install manual for a similar Carrier furnace. Read p25 to determine your pipe size and allowable elbows and max feet of pipe. Read p31 for what the termination should look like. Try get the one for your furnace but in a pinch this manual may work. Once again that furnace can be picky about the termination. I did one once with an open tee on the end and it recirculated and kept freezing up. May look simple but it is not. Other brands like Goodman don't seem as picky.
http://www.docs.hvacpartners.com/idc...58mxa-10si.pdf
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Old 02-01-2011, 01:33 AM   #15
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Did I create an intake problem?


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Originally Posted by MikeKy55 View Post
Well, lots of good info here for sure. At this point the lessor of the evils in my mind is to remove the concentric, replace it with separate intake and vent pipes thru the wall and bring the ends up thru the deck there. The furnace is located directly below the kitchen dead center, so thats not an attractive option. I wouldn't have room for the necessary elevation going out even if I could drop below the deck joist (which it appears I can't). The joist run parallel to the house, so I couldn't go that way even if the rise wasn't needed.
It never occurred to me that the concentric was that picky. I should have checked into that prior to building the deck. But I would have been doing something like this then, because the deck had to built as it is.

Quick question, is PVC PVC? or is this a special type?
Its not the concentric thats picky, nothing will vent or bring in air from that space. What about the old furnace vent? its either capped off with nothing using it anymore or its got the water heater venting through it. If its abandoned use it as a chase, this will be better than having it exhuast up through the deck (which is a code violation in most places, you can't have exhaust venting into a walkway unless its 7' above) and its a hell of a lot better than having exposed pipe running up the side of your house. It has to be schedule 40 PVC

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