# heat pump question - condenser to resistance heat?



## saichele (Nov 11, 2014)

Recently relocated to southern PA and a house with a heat pump.  Wood is pricier than I'm used to, electricity is less.  So we've had the heat pump running occasionally the last couple weeks.

Now that we're down around freezing at night, how do I know when it trips from heat pump to straight resistance coil heat?  

Thanks.
Steve


----------



## Clarkbug (Nov 11, 2014)

Easiest way I have found will be the smell.  The first few times you hit the heater strips they burn any dust off of them.  Don't know how else to describe it other than "it smells like heat".

The more precise answer would be to ask what you have for a heat pump and thermostat.  That will help determine what activates the heater.  Some units base it on the delta between room temp and setpoint, or you might have to activate the heater yourself (the thermostat would have an " Emergency Heat" setting)


----------



## DBCOOPER (Nov 11, 2014)

It depends. I have a Trane and the thermostat is what calls for backup heat. When the setpoint gest to be about 2 degrees above the actual temperature(meaning the heat pump can't match the load) the resistance heat kicks in. The compressor continues to run. It will turn on if I raise the setpoint by more than two degrees. It also runs anytime the heat pump goes into its defrost cycle. The information should be in the thermostat manual.


----------



## woodgeek (Nov 11, 2014)

Either play with your thermostat, or try to google up the manual for your thermostat.

In southern PA, unless the HP is ancient (say 1900s), you should never 'lock out' the compressor, and just let the 'aux' or strips help out as needed as a 'second stage'.  

That said, many HP installers set up the compressor to lock out at some high temp, like 30°F, to avoid callbacks, and the difference can be several hundred dollars a year extra in utility bills.

It is worth your time to research this issue and get it right.

AS for your original question....the stat will prob say 'aux' or 'second stage' when it is running...sometimes the air from the registers gets noticeably hotter, or the speed of the blower steps up (and gets louder).  Or you can just switch off the breakers to the aux strips, and see how cold it has to get outside before your compressor runs 100% and you start to get cold inside!


----------



## sloeffle (Nov 11, 2014)

My thermostat has a big red light that comes on when it calls for aux. I call it the money light.


----------



## saichele (Nov 11, 2014)

OK.  The smell of resistance coils cooking makes a lot of sense, as does switching off the breakers to the coils.  

FWIW the thermostat is a RoberstShaw 9420, and the HP is a York 25HCA348A300.  Google doesn't turn anything up on that model.

we probably haven't tripped into Aux yet, it's only gotten down to 28F or so, and the 30yr old house is much tighter than the 100 yr old house we came from.


----------



## woodgeek (Nov 11, 2014)

I got a pdf of the manual here:  http://www.manualslib.com/manual/141466/Robertshaw-9420.html

Looks pretty primitive for 2 stage control....if the temp gets 1° below setpoint, it turns on first stage, if it gets 2° below, it waits 20 mins and activates second stage.  The temp diffs and delay are adjustable.

It looks like it displays one 'flame' icon in first stage, and two 'flame' icons when the aux is being called.


----------

