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Old 05-11-2010, 07:18 PM   #1
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Moving gas furnace & water heater together


I would like to move my furnace & water heater (both natural gas fired) closer together. Currently furnace is located in a bathroom adjacent to the garage. Water heater is located in the garage about 12ft away from the furnace. The exhaust vents from both meet at the center to a T vent and goes up through the roof. Both are not direct vented.

I'm replacing the furnace (gonna get a pro to do it), so I thought I'd take this chance to relocate the furnace to a less awkward location. I'd like to basically move the furnace and water heater to the center where the vent goes up the roof and build a "utility closet" there. It makes sense to me since they both require the same rough-ins (gas pipe, exhaust air, & intake air if I choose a direct vent model), and I can just split them with Ys or Ts.

Other than the clearance requirements for the individual appliances by themselves, is there anything to watch out for when placed together? Clearances between the two? Any code issues with sharing the pipes & vents?

I have future plans of creating a hallway to lead from main living space to the bathroom area, which will run right by the "utility closet" such that the access door to the utility closet is accessed in the hallway, making it part of livable space. Is there anything that should be done different when installing furnace & water heater in livable space?

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Old 05-11-2010, 07:36 PM   #2
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Moving gas furnace & water heater together


ALL depends on local and state gas and building codes and we don't know them. I would get some Pro advice from a gas fitter and a local renovator or go to/phone city hall and see if you can talk to someone in the mechanical/building inspections dept.

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Old 05-12-2010, 05:27 AM   #3
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Moving gas furnace & water heater together


The utility room would need a solid door. Or else it will take combustion air from your living space. Which increases your heating bill, and lowers your humidity in the winter.

I think you'll need a contractor on site to tell you what can and can't be done(space constraints). Along with a code check.
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Old 05-13-2010, 01:28 PM   #4
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Moving gas furnace & water heater together


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The utility room would need a solid door. Or else it will take combustion air from your living space. Which increases your heating bill, and lowers your humidity in the winter.

I think you'll need a contractor on site to tell you what can and can't be done(space constraints). Along with a code check.
even if direct vented? Will the solid door need weatherstripping/gasket to seal it?

yes, i think this job will go to a pro.
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Old 05-13-2010, 06:50 PM   #5
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Moving gas furnace & water heater together


Weather stripping to keep the cold combustion air in the room. And CO from being drawn into the house.

Direct vent units. Each require their own separate combustion air, and exhaust pipe. So you would need to run a new pipes, instead of teeing like you said.
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Old 06-02-2010, 04:27 PM   #6
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Moving gas furnace & water heater together


talked to an HVAC guy today.

1) he didn't understand the term "direct vent", is that not the correct terminology in the industry? I had to describe it as a pipe inside a pipe where the outer is for intake air, then he said "oh that's for 95% only".

2) if doing a closet with 95% furnace that draws air from outside through the direct vent, he said the closet still needs to also have air supply from somewhere for "combustion air". That confused me, I thought the intake air is what's used for combustion. Then he explains that it's to prevent the vacuum effect when you open the closet door. Is this correct?

3) He also said my house approx 1800sq ft (1100 upstairs, 700 downstairs) would require about 90000btu. That seems awfully high to me, even using the 40btu per sqft rule.


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Weather stripping to keep the cold combustion air in the room. And CO from being drawn into the house.

Direct vent units. Each require their own separate combustion air, and exhaust pipe. So you would need to run a new pipes, instead of teeing like you said.
Can you use something like this to split the intake & exhaust vent, then T off of that?

Last edited by acerunner; 06-02-2010 at 04:52 PM.
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Old 06-02-2010, 05:17 PM   #7
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Moving gas furnace & water heater together


That tech doesn't know what he is talking about. There are direct vent 80% gas furnaces, and oil furnaces.

And that is a concentric vent.

Its what used so that you only have one hole in the wall or roof, per direct vent appliance.

And it connects directly to the water heater. And if your using a concentric on a furnace. It connects directly to the furnace.

He is sizing by a bad rule of thumb. Call other contractors.
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Old 06-02-2010, 07:53 PM   #8
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Moving gas furnace & water heater together


What kind of water heater are you thinking about? Are you still thinking a standard 70% efficient water heater with 95% furnace?
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Old 06-03-2010, 02:59 AM   #9
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What kind of water heater are you thinking about? Are you still thinking a standard 70% efficient water heater with 95% furnace?
not sure about water heater yet. But yes to 95% furnace.
What difference would the efficiency of water heater make?
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Old 06-03-2010, 09:58 AM   #10
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not sure about water heater yet. But yes to 95% furnace.
What difference would the efficiency of water heater make?
Most water heaters are not very efficient. The ones that are more then 70% efficient are very expensive..

I don't think you can T the water heater with the furnace unless you stick to a 80% furnace and 70% water heater and use B-vent, not PVC. Then you will need enough combustible indoor air which kinda sucks.

The standard water heater (and 80% furnace) typically needs a "Natrual draft" B-Vent type of venting. The B-vent is galvanized steel with an aluminum liner. The water heater is inefficient because it needs the waste heat to create the natural draft.

If you look a the 95% furnace, it uses PVC pipe for the vent because the waste is only 80 degrees.. 80 degree air is not going to rise on it's self so you need a blower to get it to go out. If you tried to T this, then when one appliance is on, the other would be blowing into the off one. Code is going to barf all over this. They use PVC because all the cracks in the vent need to be sealed, because unlike natural draft, the CO2 and the nasties are now pressurized and will escape through any cracks and come into living spaces and make problems for your health etc..



They make water heaters with blowers, they also make on-demand water heaters with PVC venting, but in either case I don't think you can T them together.

You are likely going to wind up with a standard water heater and a 95% furnace and two separate vents.

I have the two in one vent on my furnace where the inlet air comes in around a little ^ and the exaust goes out the middle and it works great, it looks much better then the vents with the little wrap around vent and straight vents right next to each other..


If you want to shove it in a closet and not use indoor combustible air you could get a 95% furnace, a 90-95% on demand water heater.

Take the two pvcs from each into their own concentric vent combiner and then run two vents out from your closet. (actually 4 vents, but only two come out your house)

http://www.htproducts.com/literature/lp-166.pdf

Whats more important to you? Only 1 vent or not using indoor combustible air?

Last edited by zootjeff; 06-03-2010 at 10:27 AM.
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Old 06-03-2010, 11:17 AM   #11
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Moving gas furnace & water heater together


Standard gas water heater will have a min AFUE of 78%.

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