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svento
Ventilation in furnace closet

We recently purchased a home in San Jose, CA that was built in the 50s. I'm natively from a place with basements where the the furnace always is located. However, in our home here, the gas furnace and gas water heater are located in a small utility room (in the center of the house), which is accessible via a door inside a closet. I've noticed that this utility room has both a floor vent (into a vented crawl space) and a ceiling vent (into a vented attic). Although I am sure this is the safest way to go, is it necessary? It seems like a huge amount of heat escapes through the vent. Although the vents are separated from other rooms by 2 doors, it still seems like a lot of heat can escape under the doors. I'd love to close up these vents if it won't cause other problems. I know that open combustion devices need an air source, but does this need to be into cold spaces? Note that both the furnace and water heater are "normal" top venting (low efficiency) types. Thank you!

MLB Construction
Re: Ventilation in furnace closet

they absolutely have to be well vented. the setup you have seems to be fine but there other options. you can install the upper vent through the upper wall directly to the outside instead of the attic. i can't see any benefit in moving the lower one unless the crawl space itself is not vented to the exterior at all. at for drafts, you can weather seal the utility room door so that no drafts enter the house

svento
Re: Ventilation in furnace closet

Thank you. I suppose you are probably right that insulating the door might be the easiest way to stop drafts. I didn't exactly say this, but I was hoping to close off the vent instead because the heater itself produces a lot of heat locally, so keeping this heat in the conditioned space made sense to me.

I am curious why you suggest venting the ceiling vent directly outside (instead of to the attic)? Is this to eliminate putting hot air into the attic? I can't see any way it would stop heat loss, so just curious.

dj1
Re: Ventilation in furnace closet

Both the furnace and the gas water heater have to be vented to the outside, not the attic. Use a separate vent for either appliance.

The reason is CO2.

svento
Re: Ventilation in furnace closet

Sorry, maybe I wasn't clear: Both furnace and water heater exhausts are vented to the outside properly in ducts. What I am questioning (and calling a vent) is basically a hole with screen over it in the floor and the ceiling of the utility room.

MLB Construction
Re: Ventilation in furnace closet

dj, his concern is getting combustion air into the utility room, which is needed. he has his exhaust vent all taken care of.

dj1
Re: Ventilation in furnace closet
svento wrote:

Sorry, maybe I wasn't clear: Both furnace and water heater exhausts are vented to the outside properly in ducts. What I am questioning (and calling a vent) is basically a hole with screen over it in the floor and the ceiling of the utility room.

The "holes" are to make sure there is plenty of air coming to the appliance room, especially to the furnace. Don't close them.

If you have heat escaping out of the furnace, then you must have a leak in your system. Have you had your heating/cooling system tuned up and serviced?

By the age of your house I can assume that you need an a/c tech or a plumber to check them out.

svento
Re: Ventilation in furnace closet

Ok, so I get the concept of needing combustion air... but in my previous houses the furnace was in the basement with no vent to the outside. So is the difference here simply the fact that the utility closet is relatively small in size? I guess I'm trying to understand why the combustion air need to come directly from the outside instead of coming from the living space. (Yes, I am sure in a new home with tight construction, this could lead to a problem, but the house was built in the 50s and isn't very tight.)

And I am not sure heat is exactly escaping the furnace (it's only maybe 10 years old), but the furnace itself seems to be radiating heat just based on the fact that a large flame is burning a few inches from the surface!

HoustonRemodeler
Re: Ventilation in furnace closet

The extra vents could be from days of yore when proper venting wasn't to code. Have a professional, licensed HVAC come out and tell you if your local code authority will allow you to close those vents.

Its amazing how long old code lingers on the books. In my fair city we still are required to have a separate shut off switch for the dishwasher.

dj1
Re: Ventilation in furnace closet
svento wrote:

Ok, so I get the concept of needing combustion air... but in my previous houses the furnace was in the basement with no vent to the outside. So is the difference here simply the fact that the utility closet is relatively small in size? I guess I'm trying to understand why the combustion air need to come directly from the outside instead of coming from the living space. (Yes, I am sure in a new home with tight construction, this could lead to a problem, but the house was built in the 50s and isn't very tight.)

And I am not sure heat is exactly escaping the furnace (it's only maybe 10 years old), but the furnace itself seems to be radiating heat just based on the fact that a large flame is burning a few inches from the surface!

Furnaces are hot when they are working. New furnaces are a little better insulated, but don't worry about heat loss, it's not that critical. By all means have a pro look at your system.

svento
Re: Ventilation in furnace closet

Thanks everyone for the info! I think for now I will simply weather seal the closet door which probably will eliminate 70% of the adjoining room's hot air leak. Next time I have a HVAC pro over I'll get an opinion on sealing the holes.

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