variable speed airhandler

MPF

analyze feedback from the system and settle themselves out to just the right speed for the application, which may be what you are experiencing. I believe if you were to vary the desired temp setting, like raise it 10 degrees, the fan would speed up to address the excessive difference the t'stat sees between actual space temp and the new, higher, desired temp. Until the two parameters agree again, that is. However not knowing what brand and model # furnace you have makes this just a semi educated guess.

Andy_17

variable speed fan

last year i put in a air handler with a variable speed fan to heat my house. the system consists of a gas boiler that supplies hot water to a heating element in the air handler. when the heat is on the airflow is low and quiet and so far seems to work well. (though it hasn't been tested thru a full heating seasin yet). my question is should i be noticing a change in the airflow at different times? shouldn't the airflow speed change somewhat? it always seems to run at the same low speed. i was wondering if thats the correct way it works or possibly the variable speed feature was not turned on when they installed it.

Mike T., Swampeast MO

Have you yet had a need for much (or even any) heat from the system? If not, it sounds to me as if it's doing just what it's supposed to do. If the boiler uses reset, I'd say there's a good chance that even cranking the thermostat in "not cold" weather wouldn't cause the blower speed to increase much, if any.

Mike2

Variable Speed Fan Coil Operation

Hi Gary..
WIthout knowing what type or mfg (of fan coil) you have I may only be guessing.. But I will guess away..

On a call for heat from your room thermostat three things should happen with two happening in parallel. First the thermostat should close a contact within its own box. That contact needs to be wired to operate an interposing relay which has two dry contacts on it. One contact should go to the fan coil circuitry telling the fan coil to gradually increase speed up to a previously selected running speed. Yes, you are correct ---- the fan speed should increase from the slow speed operation, provided that contact is wired in correctly. The second contact (on the interposing relay) should go to your pump control/ boiler logic to start the boiler and pump which supplies hot water to the (hot water)coil in the air handler ductwork.

These are (respectfully) two separate systems (control wise) which need to work together and both have their own (typically) 24 VAC electrical power supplies. This is why you want separate dry contacts in the interposing relay.

My gut tells me that if your coil gets hot, the boiler / pump portion of the control works fine. Since the fan does not increase in speed, either the jumpers (on the control board) or settings or the wiring (dry contact to start the speed increase) are not correct on your fan coil..

Good Luck... Alex