View Full Version : OT: Need help with thermostat choices.

07-07-2007, 11:09 PM
I'm wanting to replace my manual thermostat with a programmable digital unit. We currently have an A/C unit with a heat pump with emergency heat strips.

I've noticed that on some thermostats they will work with single or two stage systems. What do they mean by this stage system?

07-07-2007, 11:13 PM
On my system, the first stage of heat is the heat pump, the second adds a small strip heater (5 or 10kw - I can't remember exactly), the third is 15 or 20kw of strip heat. These stages kick in if the heat pump can't keep up.

There are also ultra-high efficiency systems (like 16-18 SEER) that have 2 speed compressors, but I doubt that you have one of those setups.

07-07-2007, 11:19 PM
A two stage thermostat works by turning the heat on in stages. With your heat pump, that means the heat pump will come on first and attempt to achieve the heat setting on the thermostat. If it not satisfying the heating requirement, IE the temperature is still dropping, the second stage heating will kick in and raise the amount of heat being generated or input into the air distribution system. There is usually a temperature setting that controls this. IE, the 1st stage (heat pump in your case) comes on at the set point you set the thermostat to, and the second stage is automatically set a couple of degrees below it.

All heat pumps have backup electric heat because there are some outside ambient conditions where the heat pump will not be able to work efficiently enough for the heating requirements.

PS You need to make sure the thermostat you buy is compatible with your heat pump. It has some additional control wiring not present with conventional systems.


07-08-2007, 02:25 AM
Good info so far. Don't buy an off brand stat. Stick with Honeywell or White Rogers. Most of the stuff Home Depot and Walmart sells is junk.

Edited to add:
If you have a Rheem unit, they energize the reversing valve solenoid in heating not coolong mode. Every other manufacturer is opposite so if the coil fails it fails to the heat mode. There should be a switch to change this action on the stat if needed.

07-08-2007, 02:59 AM

07-08-2007, 08:57 AM
Domestic application: Ground water source heat pumps work very well and is not usually subject to the outside ambient conditions inefficiencies. You would put 2 water wells in separated by a hundred feet of so and you have a ready and reliable source of 60-70 degree F water (depending on your location and depth of water table). Since you pump out of one well and into the other you do not upset the water table levels.

Evaporative cooling works extremely well in low humidity environments, but does input a lot of moisture into the building.


07-08-2007, 10:25 AM
Pardon my ignorance, but what does SEER mean?

07-08-2007, 11:44 AM

07-08-2007, 11:50 AM
"If you don't like Melbourne weather, just wait 15 minutes"
The same apples to Cerberus :D

07-08-2007, 12:54 PM
Seasonal Energy Efficiency Ratio: The total cooling of an air conditioner or heat pump in BTUs during its normal annual usage period for cooling divided by the total electrical energy input in watt-hours during the same period.

07-08-2007, 01:09 PM
OK, you're asking a good question & getting some good advice. Joel, Meho & DENed are on the right track as to the operation and I agree with the statement to stay away from anything other than the well known brands like Honeywell, White-Rogers etc. The Hunter, Homecraft, Mastercraft & other no-name & sticker-brands have a history of problems. (I've seen them half wave rectify the 24 volt AC control current & make a gas valve on a furnace chatter loudly. Great wake-up alarm....) Some are just cheap junk anyway.
As to what you need as a thermostat, you can get heat only; 2 stage heat, 1 stage cool; 2 stage heat & cool; depends on what you have for equipment.
If you have only single stage heating, there's no point in having a 2 stage heating thermostat.
A local HVAC controls supplier should be able to help you. As mentioned you will have to pay attention to the wiring with the heat pump. (Probably atleast a 5 conductor cable.) Hope you have the install manual for the system.
Check out Honeywell's website. Lots of information available & all manuals are available on line.
Hope that helps;

07-09-2007, 11:45 PM
Thanks for the help guys. Armed with this information I should be able to make a bit more of an educated decision.