Hey folks,
I live in a second floor apartment with a gas forced air furnace. The
furnace and water heater (both gas) are located in an interior closet.
In addition to the water heater and furnace flues, there is another 4"
pipe that comes through the ceiling and ends near the floor with only an
open elbow (not connected to anything). I assume this is a combustion
vent. Cut into the large duct coming out of the top of the furnace (is
this the plenum? -- sorry for my ignorance of HVAC terminology), there
is a large heating vent that serves only the closet. As a result, the
closet interior (being fairly well closed off from the rest of the
apartment except for about a 3/4" gap at the bottom), is always several
degrees warmer (or cooler, if the AC is running) than the rest of the
apartment. I have not measured the temp., but I would estimate that it
gets to be about 75-80 degrees in there when the thermostat is set to
65. It seems to me that this is at best an inefficient use of heat, and
I might get better performance by covering up the vent. Not being well
versed in all things HVAC, however, I have a couple of questions:
First, is there a legitimate purpose for having that vent in there? For
example, is it necessary for the combustion vent to function or
something like that? Another way to put this would be "will I run into
trouble by covering the thing up?" I have CO detectors installed, but
I'd sooner avoid producing a situation where they might go off than have
to figure out if they went off because of something I did.
Second, is covering the vent likely to have a noticable effect on:
a) performance of the heater (which is already not bad),
or b) efficiency of the system (which I am not thrilled with. It is,
according to the "EnergyGuide" label, near the bottom of the heap in its
class, as one might expect from a unit in an apartment where the
installer/landlord isn't paying the heating bill. Also, my heating bill
for December was seemingly extremely high for a one-bedroom apartment,
even considering an average temperature somewhere in the high teens or
low twenties.)
Any help would be greatly appreciated. Thanks guys!
-AD
I'll preface by stating that I am not a HVAC tech, but I am a mechanical and
energy code inspector.
I sounds like you are unintentionally conditioning your attic. The
combustion air setup you described is not up to current code. There should
be 2 pipes coming from the attic. One should extend to 12 inches from the
floor (like the one you described), and the other should be 12" from the
ceiling, and both should extend 12" above the insulation level (about 2 feet
total) into the attic, and be unscreened (so insulation or other debris
cannot block it).
Also, the door to closet should be sealed (think of it as another part of
your attic). I would weatherstrip the door, and block the bottom somehow.
Sealing that room will almost eliminate the possibility of backdraft, and
any CO problems you might have (keep the detectors).
It sounds like you have an upflow unit (return air on the floor). I would
recommend sealing the wall cavity above the return.
When you have the closet door closed, the vent is creating positive pressure
in the closet, and blowing all of your conditioned air through the pipe, and
into your attic. You should be able to seal the vent, but get the proper
combustion air before you do it. You will probably notice a nice difference
in your bill.
Rob
IECC 2004
IRC 2004
"Adam Diehl" <[email protected]> wrote in message
news:[email protected]...
> Hey folks,
>
> I live in a second floor apartment with a gas forced air furnace. The
> furnace and water heater (both gas) are located in an interior closet.
> In addition to the water heater and furnace flues, there is another 4"
> pipe that comes through the ceiling and ends near the floor with only an
> open elbow (not connected to anything). I assume this is a combustion
> vent. Cut into the large duct coming out of the top of the furnace (is
> this the plenum? -- sorry for my ignorance of HVAC terminology), there
> is a large heating vent that serves only the closet. As a result, the
> closet interior (being fairly well closed off from the rest of the
> apartment except for about a 3/4" gap at the bottom), is always several
> degrees warmer (or cooler, if the AC is running) than the rest of the
> apartment. I have not measured the temp., but I would estimate that it
> gets to be about 75-80 degrees in there when the thermostat is set to
> 65. It seems to me that this is at best an inefficient use of heat, and
> I might get better performance by covering up the vent. Not being well
> versed in all things HVAC, however, I have a couple of questions:
>
> First, is there a legitimate purpose for having that vent in there? For
> example, is it necessary for the combustion vent to function or
> something like that? Another way to put this would be "will I run into
> trouble by covering the thing up?" I have CO detectors installed, but
> I'd sooner avoid producing a situation where they might go off than have
> to figure out if they went off because of something I did.
>
> Second, is covering the vent likely to have a noticable effect on:
> a) performance of the heater (which is already not bad),
>
> or b) efficiency of the system (which I am not thrilled with. It is,
> according to the "EnergyGuide" label, near the bottom of the heap in its
> class, as one might expect from a unit in an apartment where the
> installer/landlord isn't paying the heating bill. Also, my heating bill
> for December was seemingly extremely high for a one-bedroom apartment,
> even considering an average temperature somewhere in the high teens or
> low twenties.)
>
> Any help would be greatly appreciated. Thanks guys!
>
> -AD