I've never had a forced air system. I'm looking at an apartment which has
forced-air heat and a/c. Do these systems pull in fresh air from the
outside or just recirc air in the apartment? I ask because the windows in
this unit aren't going to make it simple to stick a fan in and do my own
airing out of the apartment.
AC doesn't use air for combustion--no need to get outside air. 80%
efficient furnaces use inside air for combustion--it (combustion air) gets
replaced by sucking air into the house anyway possible--through windows,
cracks, outlets etc. 90+% furrnaces use outside air for combustion. All
air is recirculated, eliminate drafts.
In most newer (i.e. tightly sealed) buildings, there isn't enough air
exchange through walls, doors, and windows. Google for 'sick buildings'
of 1970s and 80s. So most newer buildings have a small intake on the
return air to provide fresh outside air.
Depending on the age of the building, it could have fresh air intake or not.
You should ask either the super or possibly
the municipal building permits office. In Ontario,
Canada, the building code was changed approx.
1980 to require outside air intakes for all forced-air
furnaces (and my house was retrofitted, but I do
not know if this was mandatory on the (government)
Is the fresh air for general circulation or just for combustion? Many codes
call for outside air for combustion in the heat exchanger, but nothing on
the house side that is circulated. That may have changed also though.
not likely that the hvac system can do a fresh air change in most
apartments, depending on the climate and sometimes on who pays for the
utilities, of course.
Patrick Maloney wrote:
I've owned and lived in many homes here in the northeast USA and have
never seen one that has an outside air intake for mixing with the
conditioned air. Newer homes do tend to have air intakes to bring in
air for combustion. They do this to avoid sucking air from the
basement, which in turn leads to conditioned air being lost, and cold
outside air being drawn in to the rest of the house.
Unless the house is built for high energy efficiency and specifically
sealed extra tight, the house will have enough leakage that bringing in
air is not necessary. In fact, folks go to great lengths to seal off
significant sources of leakage to avoid wasting energy. On the rare
occasions when you do need to ventilate, like after burning something
on the stove, just open a window or door.
If you do insist on venting, then the best way is to have a heat
exchanger that transfers air from the outgoing air to the incoming,
recovering most of the energy that would be lost if you just open a
window or pump in outside air. Houses that are super sealed for
energy efficiency use these.
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