Heat Pump Fundamentals

Manning Formula · #1 11-06-2009, 11:18 AM

Hey guys, my usual place is over in the plumbing section but I have very simple (personal) hvac question.

I have an old house with a new Trane 2.5 ton heat pump in the basement. It's wired into one of those old brown Rheem rectangular thermostats.

Now, I don't know a whole lot about hvac, but I do know when something isn't right.

For the past week or so, I've been setting my thermostat at 67 or so, with the heat on. It does ok right there, but i'd like to set it lower. When I do turn it down, even a hair, it'll come on only during the night and run the auxiliary/emergency heat the entire time it's on. If I turn it down to 65 or 64 during the day while i'm at work, it won't run all day, leaving it to catch up as soon as it gets cold and I understand that this can also be bad (economically)

Is this a thermostat issue, or am I missing something here? I obviously don't want the auxiliary heat to come on at all. How do I prevent this? I'm trying to be as economical as possible here, not as warm as possible if you catch my drift.

blueeyedsunshine · #2 11-07-2009, 01:28 AM

Hello, sir. The problem with a mercury stat is that the usual wiring causes the electric strip, or "emergency heat, to come on only a degree or two below the setting of the heat pump supplied heat, wheras on many electronic stats you can set the "differential" at any amount, say for freeze protection only. Bear in mind that you can also leave the present stat and wire in an outdoor thermostat that wont let your strip heat come on at all above an adjustable outdoor temperature, usually the "balance point" whivh is the outside temperature that the heat pump output equals the heat loss of the house. Call a good local HVAC contractor or friend in the industry to come out and do this for you unless you know exactly how to do the wiring. Believe me it will pay for itself!