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Old 07-22-2007, 03:59 PM   #1
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Proper venting for hall water heater and furnace


Our house has an upflow furnace/acoil and water heater in a hallway closet. A hole was cut into the ceiling and a wall vent screwed over it in the closet. This is basically a vent into the attic. I assume this was to allow fresh combustible air in for the furnace and water heater. The problem is I get 100 degree air coming down from the attic which heats the master bedroom closet as well as an entryway for who knows what.

I assume this was done for safety reasons, but wonder if it is necessary to have this hole. Could the hallway door have a vent to get fresh air? Should I speak to the local inspector to find out if the hole is necessary?

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Old 07-22-2007, 04:50 PM   #2
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Proper venting for hall water heater and furnace


Personally, if it was me, I would close up the vent to the attic, and put the vent in the door of the HVAC closet.

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Old 07-23-2007, 07:59 AM   #3
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Proper venting for hall water heater and furnace


Are these gas appliances? If it is, the vent supplies fresh combustible air. I would not rely on the vent in the closet door to provide adequate amount of new air unless your house is REALLY drafty. Rather go into the attic and extend the vent through the roof and put a 180* degree turn to keep water out (the inlet is now pointing down). This way your pulling in outside air and at least not super heated attic air.

Ideally there would be a PVC pipe doing this and not a chase in the closet wall...but it's cheaper and easier.

Inspector no. HVAC pro yes.
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Old 07-23-2007, 09:47 AM   #4
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Proper venting for hall water heater and furnace


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Are these gas appliances? If it is, the vent supplies fresh combustible air. I would not rely on the vent in the closet door to provide adequate amount of new air unless your house is REALLY drafty. Rather go into the attic and extend the vent through the roof and put a 180* degree turn to keep water out (the inlet is now pointing down). This way your pulling in outside air and at least not super heated attic air.

Ideally there would be a PVC pipe doing this and not a chase in the closet wall...but it's cheaper and easier.

Inspector no. HVAC pro yes.
I spoke to the city inspector this morning and he let me know that it does need to be vented to outside air. I like your idea of venting it directly outside instead of from the attic. Can I just use a simple single wall metal duct pipe that is flashed on the roof with a cap? I would then just extend this straight down into an AC supply box attached to the closet ceiling. I could trim it out in the closet with a grill. Think that would be a safe solution?

Thanks for the help!
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Old 07-23-2007, 10:12 AM   #5
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Proper venting for hall water heater and furnace


It sounds like it could work...it may be worth consulting with a HVAC pro to see if there's some other option out there that might be able to slow down the convection air flow especially in the winter.

In one house I had a similar vent that was just a metal pipe that terminate in a 5 gallon bucket. On the end of the pipe, there were very long triangles cut out with the points resting on the bottom of the bucket. When there was no call for air, the cold air would settle in the bucket, and create an air dam.

Maybe someone else here will chime in and offer some advice...
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Old 07-23-2007, 12:44 PM   #6
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Proper venting for hall water heater and furnace


If your house is so airtight, that fresh air needs to be exchanged with inside air for the Furnace & Water heater, then you may want to look into a fresh air exchange system. Otherwise, the combustible gases from the exhaust will go out the flue system to the outside, and the inside air will supply combustable air for the use.

Problem with running a duct down from the outside for use by the units, would be if there was no dampner in place to close in case of fire, you would be supplying fresh air to feed a already out of control situation.
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Old 07-23-2007, 09:22 PM   #7
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Proper venting for hall water heater and furnace


COMBUSTION AIR: You need to know the input btu's of the furnace and water heater. Then you need one square inch of free air space for every 100 btus of burner. Technically you need one vent within one foot of the floor and one with in one foot of the ceiling. The amount of free area is also cut down by the face of a grill, so size for that as well. Have a longer talk with your local authority if you are going to do this yourself.
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Old 07-23-2007, 09:31 PM   #8
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Proper venting for hall water heater and furnace


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. Think that would be a safe solution?

Thanks for the help!
Only if it is sized properly, you don't want to deplete the oxygen in the house from combustion, especially in a bedroom.

Just to clear the air......
Combustion air, is the air needed for fire to burn, "combustible" air would be explosive.

Last edited by MechanicalDVR; 07-23-2007 at 09:34 PM.
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Old 07-23-2007, 09:31 PM   #9
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Proper venting for hall water heater and furnace


I have seen some fresh air installs in mechanical closets where as I described that it is a duct that brings in the fresh air, but has a damper to close in case of fire, and also does not allow for direct to the outside air without the use of an air exchanger system.
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Old 07-24-2007, 06:45 PM   #10
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Proper venting for hall water heater and furnace


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I have seen some fresh air installs in mechanical closets where as I described that it is a duct that brings in the fresh air, but has a damper to close in case of fire, and also does not allow for direct to the outside air without the use of an air exchanger system.
You don't need a damper in a residential installation.
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Old 07-24-2007, 10:17 PM   #11
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Proper venting for hall water heater and furnace


You guys are giving incorrect answers. The reason the door vents have been sealed off is because of safety concerns. There is a chance that carbon monoxide could leak into your house. It is code in my area to seal the door vents and drop a high and low combustion pipe. Single wall pipe is all that you need. Double wall pipe would be a waste of money. Also, do not run your combustion air to the outside. This is another way for you to throw away your hard earned money. I would shake my head if I ever saw this. I was a little confused by your post. You say the furnace and hot water heater are in the hallway closet yet the attic air heats your master bedroom closet. The furnace and hot water heater should be in a closet of their own and sealed. I hope they aren't in your master bedroom closet. You need to think of it as a separate room that is to be left unconditioned. That air should not come in contact with you heated/cooled air. There should be a divide. Your return air that goes into the unit should not be pulling in through your combustion air vents. If so, you need to seal the closet better. Your attic has enough ventilation to provide combustion air. Do not risk roof leaks by cutting in a goose neck flashing.

Last edited by Malcolm; 07-25-2007 at 07:31 AM.
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Old 07-25-2007, 10:29 PM   #12
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Proper venting for hall water heater and furnace


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You guys are giving incorrect answers. The reason the door vents have been sealed off is because of safety concerns. There is a chance that carbon monoxide could leak into your house. It is code in my area to seal the door vents and drop a high and low combustion pipe. Single wall pipe is all that you need. Double wall pipe would be a waste of money. Also, do not run your combustion air to the outside. This is another way for you to throw away your hard earned money. I would shake my head if I ever saw this. I was a little confused by your post. You say the furnace and hot water heater are in the hallway closet yet the attic air heats your master bedroom closet. The furnace and hot water heater should be in a closet of their own and sealed. I hope they aren't in your master bedroom closet. You need to think of it as a separate room that is to be left unconditioned. That air should not come in contact with you heated/cooled air. There should be a divide. Your return air that goes into the unit should not be pulling in through your combustion air vents. If so, you need to seal the closet better. Your attic has enough ventilation to provide combustion air. Do not risk roof leaks by cutting in a goose neck flashing.
How would you know that his attic is ventilated enough to provide combustion air without seeing the house?
And I guess you can start shaking your head now, newsflash.... more often than not outside air is used for combustion air, most new furnaces are piped directly to the outside for combustion air and it doesn't change the heating output of the furnace. Check your facts.
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Old 07-26-2007, 09:44 AM   #13
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Proper venting for hall water heater and furnace


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How would you know that his attic is ventilated enough to provide combustion air without seeing the house?
And I guess you can start shaking your head now, newsflash.... more often than not outside air is used for combustion air, most new furnaces are piped directly to the outside for combustion air and it doesn't change the heating output of the furnace. Check your facts.

The attic has to have some attic ventilation. Moreover, they are not completely sealed. If there isn't enough ventilation from the attic for combustion air, they need to have that addressed. In my area no one vents to the outside on an 80 percent unit, so yeah buddy I can shake my head all I want. Your news flash means crap because everything is regional. My point is that you guys are giving the OP advice that doesn't need to be done. It is fine the way it is. Are you kidding me? You think an attic doesn't have enough combustion air to supply a furnace and water heater. Before a problem would arise, a person would have to intentionally seal the attic. There has to be at least a ridge vent, soffits, or a gable vent in the attic. Most have soffits with some kind of ridge vent or equivalent. I have never seen a house without any of these, and I know you haven't either. I have seen hundreds of houses retrofitted with the door vents sealed and the high and low combustion dropped. I have done quite a few myself. People may vent to the outside in your area, but it isn't needed in this situation. They obviously do the same thing in my area and the area in which the OP resides. Therefore, it doesn't matter what they do in your area as everything in construction is regional. You and I both know it. Your an idiot for thinking any builder would seal an attic so tightly with absolutely no attic ventilation. They would have ice damning, sheathing problems, moisture problems, paint bubbling/cracking, shingle failure, etc... by now if it was sealed so tightly that there wasn't enough ventilation for combustion air. You need to learn more about the total construction process before trying to give a person advice on something that is a waste of money and could lead to future problems.

Last edited by Malcolm; 07-26-2007 at 03:07 PM.
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Old 07-26-2007, 07:19 PM   #14
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Proper venting for hall water heater and furnace


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The attic has to have some attic ventilation. Moreover, they are not completely sealed. If there isn't enough ventilation from the attic for combustion air, they need to have that addressed. In my area no one vents to the outside on an 80 percent unit, so yeah buddy I can shake my head all I want. Your news flash means crap because everything is regional. My point is that you guys are giving the OP advice that doesn't need to be done. It is fine the way it is. Are you kidding me? You think an attic doesn't have enough combustion air to supply a furnace and water heater. Before a problem would arise, a person would have to intentionally seal the attic. There has to be at least a ridge vent, soffits, or a gable vent in the attic. Most have soffits with some kind of ridge vent or equivalent. I have never seen a house without any of these, and I know you haven't either. I have seen hundreds of houses retrofitted with the door vents sealed and the high and low combustion dropped. I have done quite a few myself. People may vent to the outside in your area, but it isn't needed in this situation. They obviously do the same thing in my area and the area in which the OP resides. Therefore, it doesn't matter what they do in your area as everything in construction is regional. You and I both know it. Your an idiot for thinking any builder would seal an attic so tightly with absolutely no attic ventilation. They would have ice damning, sheathing problems, moisture problems, paint bubbling/cracking, shingle failure, etc... by now if it was sealed so tightly that there wasn't enough ventilation for combustion air. You need to learn more about the total construction process before trying to give a person advice on something that is a waste of money and could lead to future problems.
Ever hear of the National Fuel Gas Code ? Or BOCA mechanical? Try reading them, you would learn tons. And yes I have seen many older homes that only have two small gable vents that are usually blocked with cardboard and many older homes that the only soffit vents are the 1" aluminum pop ins that had been painted over the year after they were installed. I have been in HVAC professionally 21 years and grew up in a construction family.
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Old 07-26-2007, 07:33 PM   #15
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Proper venting for hall water heater and furnace


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Ever hear of the National Fuel Gas Code ? Or BOCA mechanical? Try reading them, you would learn tons. And yes I have seen many older homes that only have two small gable vents that are usually blocked with cardboard and many older homes that the only soffit vents are the 1" aluminum pop ins that had been painted over the year after they were installed. I have been in HVAC professionally 21 years and grew up in a construction family.
How much combustion air do you think is needed here? Give me a break. You make it sound like if I spent a couple hours in one of these attics you are referring to I would suffocate. Older houses were not built air tight. We both know it. I would be more worried about attic ventilation for the problems I stated than combustion reasons on those houses. I know you mean well and all, but we both know that there is no problems drawing combustion air from the attic. Having to cut a flashing in is overkill that will produce the exact same results. The OP does not have a problem. He/she should leave the combustion air alone and spend the money on something that will bring in a a return of some sort. I would think of an technician as a crook if they recommended cutting a flashing in, running combustion pipe, etc... when there isn't anything wrong with the current situation.

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