OK, the furnace itself does have a short (foot and half or so long) piece of
PVC sticking up above the unit (parallel to the exhaust) that I assume is
its fresh air intake -- the air being supplied to the furnace/laundry room
area through that 6" ductwork from the outside. While we had them replace
the water heater at the same it time (the old one was getting pretty old)
it's rather conventional (not high-efficency -- only two of us.)
I'm hoping his particular unit is "dual certified" at this point. If not,
the combustion air would have to be piped in PVC directly to the unit. If
it's dual certified, they just brought things up to code by adding the
required air for combustion for several appliances.
Use the continuous fan or circ fan for heating and when no call for either
heat or cool. In cool mode, run fan in "auto" mode... to run continous fan
in cooling mode will actually raise the humidity in your home. Here in the
south, thats not a good thing...remember that 90% of air conditioning is
Running the fan all the time:
1) If the ducts are leaky (normally are) the air exchange rate of the
house will go up. If the house goes positive in the heating season
due to dominate return leaks. Warm moist air will be pushed into the
wall cavities and can condense. This can cause failure of the
building structure and health issues. If the house goes negative in
the cooling season due to dominate supply leaks. Warm moist air from
outside can condense in the walls and cause building structural
failure and health issues
2) If there is a central return and the doors are closed the pressures
in the house will increase the air exchange. In the rooms with supply
and no return will go positive in pressure forcing warm moist heated
air from in the house into the wall cavities. This can cause failure
of the building structure and health issues. The room with the return
will normally go negative in pressure and in the summer will pull the
warm moist air into the walls. This can cause failure of the building
structure and health issues.
So, if the ducts do not leak and there is no pressure differential
between the rooms then running the fan all the time will not increase
the heating or cooling load and not cause condensation in the wall
cavities. There are only a very small percentage of homes in the
world like this and they require special detail during design,
construction and commissioning.
The recommendation is to have a Whole House Performance contractor
test your house for this.
Seals in the windows leak: Do you mean you have thermal pain windows
(two pains of glass)? If this is the case this will not cause the
house to leak more air. Technically the conductive value of the
window will go up a minor amount since the air between the glass will
have more moisture in it. The main reason to change the window will
be for aesthetics.
Only 120 watts: Lets put this in perspective. I will make some
assumption on the cost per kWh of your local electricity. Im also
not an expert on the actual wattage of a fan motor. One has to
actually put a meter on it to get its actual wattage. Amps * Volts =
120 Watts * 24 hours per day * 365 days per year = 1,051,200 watt
1,051,200 watt hours / 1,000 watts per kWh = 1051.2 kWhs.
So if you pay $0.10 per kWh
0.10 $ pre kWh * 1051.2 = 105.12 dollars per year
If the thermal envelope is correct and the HVAC is designed correctly
one does not need to run the fan 24/7
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