My apartment's mid-90s heating system consists of a gas-fired hot water heater feeding a First Co TAQ1824 air handler. The air handler has a fan and blows hot air through air ducts. The system is described in detail in my previous post.
I recently swapped out the old Honeywell basic digital thermostat for a Nest. With the Honeywell, anytime the system was heating or cooling, the fan ran full blast and you could hear it loud and clear and feel a strong rush of air from the vents throughout the apartment, including cool air in the first 1-2 minutes it takes the air handler radiator to heat up.
With the Nest, when it calls for heat, the air handler's fan runs at a different speed - specifically, VERY SLOW. Like, inaudible unless you're right by the air handler, and you can barely feel air coming out of the vents.
After some research, I learned that typically, for gas fired furnaces, the thermostat only calls for heat (connects +24V to W), leaving it up to the furnace to decide when to turn on the fan. For electric furnaces, the thermostat calls Heat and Fan (W+G). After reconfiguring the Nest for electric heat, it now behaves like the Honeywell: anytime it's trying to heat, the fan is going full blast. I also found that the Honeywell could be configured to run in 'gas' mode the same way.
When the Nest was in 'gas' mode and the fan was running slowly, it did still heat the apartment in about the same amount of time. There was less air blowing around (more pleasant, really), but the air slowly coming out of the vents was much hotter (spending more time in the radiator), so it kind of balanced out.
Now I've got a handful of questions about this:
- Does it makes sense that the First Co air handler has two fan speeds: one for gently pushing hotter air out, and one for more forcibly circulating air? I thought multi-speed fans in HVACs was a recent higher-end feature.
- If #1 doesn't make sense, what explain the slow feed of hot air when the Nest is only connecting W? Is there some electrical leakage path that makes the fan spin slightly? If that's the case, I'm assuming it's unsafe to run in 'gas' mode.
- Ultimately, how should I have this system set up? As 'gas' so the air handler determines what speed to run the fan, i.e. very slow as described above? Or should I configure it as electric so it's always running the fan full blast? I don't have any particular reason to think the Honeywell's previous setup should be authoritative.
Note that although the hot water is gas-fired, the air handler does not use gas and doesn't really need time to heat up. It's always got hot water on tap right next to it.
Also I have not been able to find an owner's manual for the First Co air handler.