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.
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
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.
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.
Age and Treachery will Triumph over Youth and Skill
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.
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.
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.
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