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Old 10-11-2008, 06:46 PM   #1
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Need to move a gas vent...


I am framing my basement and unfortunately the gas exhaust vent ducting from the water heater and the furnace are in the way. I don't know anything about HVAC so I have no idea if it is illegal to do this so I was wondering if anyone could give me some suggestions. Basically I want to lift the ducts coming off the water heater and the furnace to a steeper angle and run the duct like the yellow lines in the first picture. It will be running next to the ducting for the heat but below the ceiling trusses. If I do this I think I will need to cut the piece that goes up through the house, but I am scared to do this because it looks like it's one piece for about the first 4 feet. The bottom of it has a groove all around it and it has "strap" like strips that run the whole length of it on the outside. What is the proper way to go about this?

Note: I really don't want to soffit it in because it will look really out of place and if I move the wall out to accommodate it I will loose a lot of precious square footage.


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Old 10-11-2008, 07:55 PM   #2
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The horizontal sections coming out of the furnace and water heater are single wall vent, just a simple metal tube. Where they join up and the pipe goes vertical...That's "type B" vent, which is double wall. Type B has an outer wall and an inner wall that is of slightly smaller diameter. Sections of type B are pre-made and basically interlock together.

Running the single wall vents more vertically is certainly not a problem. Actually it is a good thing.

What I would try to avoid is adding any sort of elbow (especially a 90*) in the B vent. A minimal amount of gradual bends in the single wall flue would be more desirable if that is achievable. If you must, gradual bends are the only way to go with the B vent. Go to a home center and take a look at the type B pipe and the fittings available.

Vent system design involves a lot of factors in order to be successful, including number of elbows, length, size, etc. Remember that there's some nasty gas going up those vents, and it can make you sick or even kill you if done in a way that renders the common vent ineffective or less effective.

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Old 10-11-2008, 08:12 PM   #3
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Need to move a gas vent...


I see no problem with what you want to do. Just make sure that you keep the pipe going up. It can never go level.

Cutting the other pipe and making it steeper is not an issue. Just be careful that you keep the next pipe in line outside of the previous pipe (which they didn't do in your first picture).

You could even put a 90 in the pipe on the left in the second picture and move it towards the pipe on the right and then use a Y to join them way back at the furnace near the furnace.

You can cut back the pipe going up in the wall to get more room if needed.

Use duct screws to connect the pipe together. No loose joints.

I can appreciate your desire to get more sq ft out of the deal but don't get greedy. I can see you have a gas water heater in there and you will need access to that space because water heaters do have a life and that life is about 10 years give or take.
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Old 10-11-2008, 08:54 PM   #4
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Need to move a gas vent...


The peice that you want to cut is the type B vent and can not be cut. It is double wall and you would ruin it if cut. Also the straps you are tsalking about are the way some companies support there pipe going up through the house. If you cut those the flue could fall out of the chase and come apart in the attic.

Also you need to have 1" clearance for double wall and 6" clearance for single wall pipe from combustables per code. You will also need to provide combustion air for the furnace room.

I would call a pro for this one as it can kill your family if not done properly.

All for a few square feet!
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Old 10-11-2008, 08:59 PM   #5
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Need to move a gas vent...


Quote:
Originally Posted by hvac122 View Post
The peice that you want to cut is the type B vent and can not be cut.
Yea, I didn't see that.
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Old 10-11-2008, 09:34 PM   #6
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Need to move a gas vent...


I am going to call a professional for it mostly because I don't know how this would be possible without cutting the duct that goes up through the floor, and I figure this is the one thing I don't want to be guessing on. Thanks for the help though everybody. I will have quite a few more questions in the future once the framing is done. Does anyone know of any good books or websites to learn about the basics of HVAC?
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Old 10-11-2008, 10:10 PM   #7
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Need to move a gas vent...


All my HVAC books are codebooks, and they're not a fun read. Taunton has a good series of books on such subjects...Not sure if they have an HVAC one.

HVAC122 mentioned combustion air, which is a very important requirement. Right now your furnace and water heater are able to take air from your basement in its entireity. When you finish the basement and wall off the unfinished part containing the appliances, you're limiting the fresh air that they need for combustion. Without ample oxygen, the combustion process becomes inefficient, the appliances burn dirty, and more carbon monoxide is produced.

Combustion air is normally achieved by installing a couple vent holes in the wall somewhere near the appliances. There are size requirements for the vents, but normally an 8x16" return grill over a hole covers it. You'll install one within 12" of the ceiling and one within 12" of the floor. That will effectively allow air to enter the unfinished space to feed combustion. A louvered door is another option. You cannot have combustion air openings from unfinished space into bedrooms or bathrooms...Stick to living spaces and hallways.

Whether or not you need combustion air depends on the size of the unfinished room and the btu/h input rating of the furnace and the water heater. Both should have stickers listing the input rating. Most water heaters are 40,000 btu/h, and furnaces vary from around 90,000 to 150,000 btu/h's. For every 1000 btu/h's of input rating, you need 50 cubic feet of room in the unfinished space, or vented connection to a room that has that amount.

Example: Room is 10' long, 6' wide, and 8' tall. That's 480 cubic feet. In that room you have a 40,000 btu/h water heater. Take 40 (40000 divided by 1000 btu/h's) x 50 cubic feet (minimum requirement). That's 2000 cubic feet needed. So in this case, you'd have insufficient combustion air and would need to ventilate the unfinished space into an adjacent living area with the remaining 1520 cubic feet you need, in addition to the 480 cubic feet you have.
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Old 10-12-2008, 05:27 PM   #8
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Need to move a gas vent...


Fortunately my basement already has the combustible air coming in right next to the furnace. It is like you said where one opens up by the ceiling and the other close to the floor. I did get a building permit for the basement finish and they require combustible air in the unfinished space, so the inspector will make sure I am good there. The louvered door idea is good to. In the wall that I would like to put in the place of the vent ducting I am going to have French doors that will open up to a rec room, I am thinking if I make them louvered doors combined with combustible air coming in from outside, that would provide an ample amount of air.
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Old 10-12-2008, 09:24 PM   #9
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Need to move a gas vent...


Sounds like you've got it 100% covered. Also, you're smart to pull a permit.

The only downside to the louvered door idea is that you'll be able to hear the furnace running a lot better, which can be problematic in a TV room or a living room.
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Old 10-12-2008, 10:10 PM   #10
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Need to move a gas vent...


"PERMIT???

we don't need no stinkin' permit, Amigo"


Who can name the movie that paraphrased from

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