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-   -   Is the venting on my furnace screwed up? (http://www.diychatroom.com/f17/venting-my-furnace-screwed-up-169886/)

Toller 01-23-2013 10:13 AM

Is the venting on my furnace screwed up?
 
2 Attachment(s)
I have a Trane XR90 furnace, 80,000 btu.
Last night at 2am I noticed it wasn't working. A red light on it was flashing three times, which the instructions says means the inlet is blocked. I went out (-10 wind chill) and found ice on the inlet. I broke that away and the furnace started working properly.
However, the vent didn't look right to me. I checked the instructions and found it was below the minimum. Attached are a photo of the installation and a clipping from the instructions. They are 7" apart when the minimum is 9" and the vent is 7" when the minimum is 12". I suppose the inlet is getting moisture from the vent and it is freezing. I also wonder if it is getting adequate fresh air, being too near the vent.
There is also a water heater vent above and to the right, which probably doesn't help any.

Presumably something has to be done, as it did fail last night. This is all below a deck. Seems to me the easiest "fix" would be to hang a sheet of something from the deck between them. That would prevent the inlet from drawing from the vent, but wouldn't do anything to restrict the air flow. Does that make sense?
Any other ideas?

I have a call into the installer (I bought a 6 year old house last fall), but am not hopeful.

joecaption 01-23-2013 10:24 AM

I'd be tempted to cut that PVC pipe that's cut at an angle to get it flat, add a 45 deg. elbow and 12" of PVC pipe. Would not even have to glue them until you see if it works.

jagans 01-23-2013 10:29 AM

Guaranteed that the deck guy came along and said "This pipe has to go" and whacked it off. Sticking a piece of plywood between in the short run makes sense to me till the temperature comes up. Do those instructions still apply in an inside corner like you have there? I doubt it.

Toller 01-23-2013 11:20 AM

Quote:

Originally Posted by jagans (Post 1100127)
Guaranteed that the deck guy came along and said "This pipe has to go" and whacked it off. Sticking a piece of plywood between in the short run makes sense to me till the temperature comes up. Do those instructions still apply in an inside corner like you have there? I doubt it.

The vent is too short because it is supposed to be 6" long between the wall and the 45 piece.

The requirement from an inside corner is 12". It is about 10".

yuri 01-23-2013 12:52 PM

You CANNOT EVER vent a furnace under a deck period. The pipes must be insulated and extended past the edge of the deck period and it does not meet code. NO matter what you do the exhaust will always recirc into the intake and that moisture will corrode the heck out of your burners etc and damage them. The moisture/exhaust needs to rise straight up and under a deck is a no no.

ben's plumbing 01-23-2013 04:12 PM

yep end of discussion....needs to be changed...ben sr

Toller 01-23-2013 07:35 PM

Quote:

Originally Posted by yuri (Post 1100212)
You CANNOT EVER vent a furnace under a deck period. The pipes must be insulated and extended past the edge of the deck period and it does not meet code. NO matter what you do the exhaust will always recirc into the intake and that moisture will corrode the heck out of your burners etc and damage them. The moisture/exhaust needs to rise straight up and under a deck is a no no.


The installation instructions say there must be 12" below an overhang, and the illustration above shows the vent directed down. Actually it projects the exhaust pretty good, though obviously not good enough.

Marty S. 01-23-2013 07:42 PM

Yuri is 100% correct. Recirculating exhaust fumes will rust out a heat exchanger in just a few years. Probably one of the worst rusted furnaces I ever saw was in a church. The company that installed it 4 years earlier switched the intake and exhaust vent terminations on a vtk so the exhaust hit the brick,turned into a cloud and promptly got sucked back into the intake. Looked like a 30 year old furnace that had never been serviced.

yuri 01-24-2013 08:05 AM

Quote:

Originally Posted by Toller (Post 1100415)
The installation instructions say there must be 12" below an overhang,They mean roof overhang, soffit of a roof line which extends about a foot or two not a 6 foot deck overhang and the illustration above shows the vent directed down. Actually it projects the exhaust pretty good, though obviously not good enough.

.....

Toller 01-24-2013 10:46 PM

Quote:

Originally Posted by yuri (Post 1100212)
You CANNOT EVER vent a furnace under a deck period. The pipes must be insulated and extended past the edge of the deck period and it does not meet code. NO matter what you do the exhaust will always recirc into the intake and that moisture will corrode the heck out of your burners etc and damage them. The moisture/exhaust needs to rise straight up and under a deck is a no no.

So far the installer won't even talk to me. I will give him the benefit of the doubt and assume he is super busy with people who don't have any heat. As long as I keep ice out of the inlet, I have heat.

But is that a solution; just running the pipes further out? That is not a big deal. I figure the pipes are 23 feet long, there are 4 elbows at 5' an elbow, and the maximm run is 50'; so I have seven to spare. Does the inlet have to be insulated or just the vent?

There is no place else he could really run to. The back wall has a deck also, and the other side is too far away with a lot of stuff in the way.

I understand this is not allowed, but I don't know why. What would happen if he just ran the vent another 6' and left the inlet where it is? The instructions say the vent has to be between 12" and 14". What bad thing happens at 15"?

I understand it is wrong to vent under a deck; but is it an actual code violation or just a bad practice? The deck is shown on the plans; so it was likely in before the furnace. (it is actually an enclosed porch; I don't know why they didn't just build a sunroom, but that is besides the point)
I appreciate the help here. The more I know the better I can deal with the problem.

Marty S. 01-25-2013 07:27 AM

PVC is cheap. Run both out past the end of the deck and do it right. Should take you a whole 15 minutes to extend and support those vents with a helping hand. Only the exhaust needs insulated.

Intake and exhaust too far apart can make the pressure switch bounce open/closed under certain wind conditions and you'll have no heat. Leaving the exhaust under the deck will ruin the decking.

jagans 01-25-2013 08:39 AM

The Pros are all telling you what to do to save your furnace from premature failure, and incredibly, arguing with their expertise, or ignoring them??????
PVC Pipe is cheap. A new furnace is expensive. Gee let me think :whistling2::whistling2::whistling2::whistling2::w histling2::whistling2::whistling2::whistling2::whi stling2::whistling2::whistling2:

Toller 01-25-2013 09:22 AM

Quote:

Originally Posted by jagans (Post 1101581)
The Pros are all telling you what to do to save your furnace from premature failure, and incredibly, arguing with their expertise, or ignoring them??????
PVC Pipe is cheap. A new furnace is expensive. Gee let me think :whistling2::whistling2::whistling2::whistling2::w histling2::whistling2::whistling2::whistling2::whi stling2::whistling2::whistling2:

Who did I argue with? Is asking for details arguing?:(

Toller 01-25-2013 09:24 AM

Quote:

Originally Posted by Marty S. (Post 1101543)
PVC is cheap. Run both out past the end of the deck and do it right. Should take you a whole 15 minutes to extend and support those vents with a helping hand. Only the exhaust needs insulated.

Intake and exhaust too far apart can make the pressure switch bounce open/closed under certain wind conditions and you'll have no heat. Leaving the exhaust under the deck will ruin the decking.

It wasn't the price, I thought separating them would give less chance for recycling the exhaust. But if it doesn't work, it doesn't work.

yuri 01-25-2013 09:29 AM

Some Trane units ( newer ones ) will allow you to vent them in 2 different places/locations/walls. I am not a TRane dealer but a highly experienced Trane guy I know told me that. New Lennox units are the same. In a case like yours we also can run the pipes up an old chimney if it is large enough and in a worst case scenario if the furnace is approved for it we single pipe it. That is running only the exhaust outside or up the chimney and taking the combustion air from inside. The installer can check with Trane about these scenarios and usualy it is in the install manual. You will damage the furnace as it needs to breathe perfectly clean air to get the right oxygen for combustion and any moisture will damage the burners and heat exchanger and void the warranty when they inspect it. You will also get pressure switch tripping problems under a deck as wind swirls there etc. Only the exhaust needs insulating and yes you do need to ACCURATELY calculate the length of pipe with equivalent feet of elbows added and the installer can do that or upsize the pipe one size ex. go to 3" from 2" to allow a longer run.


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