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Controlling a HW garage unit heater...

Last weekend came out to a cold garage. Thermostat was calling for heat, zone valve was opening and water was circulating but the fan for the unit heater would not turn on.

First boiler (Utica UB90) operated at higher water temps than the new boiler (Utica SSC) so I'm thinking it's the aquastat (Honeywell L6006C) that will need to be adjusted. Not understanding how I can control the unit heater with a wide range of temps the stat will be sensing now with the outdoor reset installed.

For now, I'd like to use the unit heater maybe thru this heating season but possibly change to baseboard or panel rads as has been suggested to me. I really don't care for the sound of the fan and or the aesthetics of a unit heater any longer.

Should also mention the garage is a two car attached with two sides on the house & two are exterior walls (21' X 21' with 9'-6" ceiling height). Any suggestions/comments welcome...


  • ratio
    ratio Member Posts: 3,601
    The grey box strapped to the bottom pipe should be the aquastat that turns on the blower. Does it have a knob, or setpoint visible from the top? With hot water flowing in the pipes, turn that down slowly until the fan comes on.

    With outdoor reset, the boiler should put out just enough heat to heat the house, the fan may need to be on continuously to keep the garage warm. It's also possible, perhaps likely, that it will not be able to heat adequately with the lower water temp. I don't have enough experience to condemn it out-of-hand, but it seems small for a space with two exposed walls, one of them mostly doorway.

  • john p_2
    john p_2 Member Posts: 367
    It worked great with the other system (higher temps)
  • ratio
    ratio Member Posts: 3,601
    Right. But with lower temps comes lower heat output. Maybe it'll be enough, maybe not. I wanted to mention the possibility. You could do a heat loss on the garage, find the output of the unit heater at various AWTs, & then you'd know with relative certainty. Or just wait & see. ;)