Heat Pump and Radiators?

[Freud]

Hi: We have a 1930s Cape Cod in MD. It has a natural gas boiler for radiators, and a heat pump/central AC system. The two systems are controlled by two separate thermostats. My question is, can I get a single thermostat which will allow me to control the two systems so I can be as energy-efficient as possible? Around here it gets cold enough so that the heat pump will doubtless fall back to its aux heat, which is quite inefficient. What I'd like is to use the heat pump when it's not too cold out, then switch over to the radiators as the aux heat. Can I maybe wire the heat pump thermostat so that it kicks on the gas rather than the resistance heat? Any ideas would be appreciated. Thanks, Freud

[Pat]

Wouldn't it be simpler to just have a qualified serviceman disconnect the heat pump's electric heat. Then just set your heat pump to whatever temp you like and your furnace to 3 or 4 degrees cooler so it will kick on when the heat pump can't handle it.

As for your question. Could you wire the heat pump's control to turn on the furnace instead of the electric heat? No. Could a qualified electrician do it? Yes. Would he? Probably not. Would it be legal? Maybe.

The problem is that would probably need a control box with a relay to interconnect the systems. That's a bit unusual and you would need to talk the electrician into doing something like that because it's a bit strange. Disconnecting the electric heat, OTOH, is just a few wire nuts or screws.

[Bob F]

I'm sure it could be done. You would probably want it set up so the heat pump would still use the resistance heat during the defrost cycle to avoid cold drafts. Basically, you'd want the auxillary heat signal from the thermostat to go to the boiler rather then the heat pump, perhaps with a relay to isolate the systems. If you are handy with electricity, you might handle it fine yourself. You could call any local heating/AC contractor and ask them what they'd charge to do it.

Bob

[Freud]

SNIP

That may be the best way, thanks.

I hadn't thought about isolating the systems - I'm not really familiar with this stuff (obviously), but it seems like there must be a way to make the best use of what we have. Thanks, Freud

[Freud]

SNIP

Thanks, I think I'd get a pro to do it. I've been looking for an all in one device that could handle this, but I guess there's not much demand for it. I had heard that it's possible to run a loop from the furnace into the duct instead of the resistance heat, so I figured that there must be a way to control both easily. Thanks, Freud

[Chris Lewis]

According to Freud :

When you install a heat pump in tandem with another system (eg: forced air gas etc), the system is usually set up to use the other system as backup. You wouldn't have electric heating strips at all.

But that doesn't seem as convenient with a hydronic system coupled with a heat pump/AC :-(

I'd have a chat with an expert at a good HVAC company and see what your options are. There's bound to be something.

Disconnecting the heater strip is easy. Whether it's advisable (is it part of defrost cycle?) is a different question.

[Freud]

The defrost cycle is yet another new thing to me - I'll get to grips with all this yet! I really appreciate all the info. Thanks, Freud

[SJF]

[SJF]

On my Carrier heat pump, the heat strips were auxiliary units and never installed. Obviously not necessary to the defrost cycle. I do use a gas furnace which preceded the heat pump as a backup unit, set a few degrees cooler than the heat pump setting.

SJF