Our single story house with basement has three heating/cooling zones. Two zones are both cooling & heating, with cooling via air conditioner and forced hot air heating via boiler fed heating loop that runs through the air handler. Each air handler has two fan speeds, but at present (only) the high fan speed is used for both heating and cooling. Third zone is for the basement and is heat only (via baseboard). The A/C, air handler & thermostats are 3 years old.

I'm interested in trying to maintain a more even temperature throughout the house. The high fan speed is fine for cooling, but the system puts out "too much" hot air when heating. The excess of hot air makes some rooms unpleasant, especially when the system runs a lot when it gets very cold.

I realize that using the lower fan speed for heating will cause the fans to run more often, but there will be less air flow (hence should be less of a blast of hot air when it runs). I would think that delivering heat at a reduced rate, but more frequently, would not increase the amount of oil we burn, as the boiler would have less time to cool down between calls for heat. Manufacturers spec sheet for the air handlers shows 1800 vs 1500 CFM (high vs low) for the larger unit, and 1400 vs 1000 CFM for the smaller unit.

So, does it make sense to use the lower fan speed for heating?

Assuming so, could I get away with installing an external switch (ie. wall switch) to select the fan speed?

Or, is it possible to wire it up so that the hot/cold selection switch on the thermostat selects fan speed? What would I need to do it this way?

Thanks
Guy

Likely what you want to do will work. More complex furnace controls do it automatically. You may even have the circuits to do it. If so, it would be much easier to figure out if you had the furnace installation guide. If you don't have such, you might even be able to find some info on the furnace manufacturer's web site. If your furnace is fairly new and has a solid state control board, you might even be able to figure it out. Look where the wires from the blower motor connect to the board. If it has separate terminals labeled heating and cooling, try connecting different leads to the heat terminal.

If not, and you can identify the power to the motor and lower speed windings, a wall switch should work. You could run the blower feed wire to the center pole of a common 3 way switch, and the high speed to one for the cooling, and a lower speed to the third one.

... lower the water's temp also have the same effect... or install proportional valve on your hw supply (assume the system is hw not steam)