Running fan continuously?

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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.)
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Ted Lee
Minnetonka, MN
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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.
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Ted Lee wrote:

constant.
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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 humidity control.
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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. I’m 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 = Watts.
120 Watts * 24 hours per day * 365 days per year = 1,051,200 watt hours 1,051,200 watt hours / 1,000 watts per kWh = 1051.2 kWh’s. 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
Andy
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