I have a single zone hot water boiler for heat and a separate system for central air, both with their own thermostats. Can I install one programmable thermostat to control both of these systems? And which thermostat do you recommend?

Thanks.

No reason one thermostat and one transformer can't work both systems. Some systems need a positive signal to shut the heat off. Make sure if that is how yours works, it is an option with any thermostat you buy. As far as which one? I would stay away from the Honeywell RTH230B. Search here, and you will find any number of problems I couldn't solve. Part of the problem is that several people were given instructions in Spanish.

Thanks Labman, Quick response! I bought the Honeywell RTH230B yesterday with the provision that I could return it, and I haven't yet opened it. (They're on Sale at Lowe's for $29.) So, without contacting a Heat and Cooling Serviceman, how can I tell if my system requires the positive signal to shut off the heat?

Also, I notice a wide range in prices in thermostats, from $30 up to $180+. Is more cost a better product, better warranty, or what should I be looking for? Checked Consumer Reports, but they make no brand comparisons or recommendations.
Thanks again.

Dave

A sure check is to look at the old wiring. If only 2 wires are connected, it doesn't need the additional signal. It there is more than a usually red wire from the transformer and usually white back to the boiler, you will need to figure out what they do if anything. There may be some directions somewhere around the boiler.

To use any thermostat for both, you will need wires to it carrying power from the thermostat, power back to the boiler and power to the relays for the A/C compressor and blower. Some thermostats require wires to both terminals of the transformer.

Okay, thanks a bunch. I'll check it out.

I know you probably have some preferences on brands, but may not be able to post them here.

Dave

There are some forums here where we have top notch professionals giving advice you can take to the bank. This isn't one of them. I am just another homeowner who started sharing some things he ratted out in his own house. I have also picked up some stuff on hot water heating at my church. Of course, over the 2 years I have answered questions here, I have picked up a little more.

I am free to say what I think here except maybe what I think of others pretending to know more than they do. When I get to the end of my knowledge, I stop. Some people have have gotten the Honeywell thermostats to work.