Heatpump and second stage heat (emergency heat)

[JimO]

I have a TR60 thermostat and a Lennox HVAC ECB29 Series heat pump.

I am trying to understand what triggers second stage heat (or the "emergency heat").

I have read that it may come on when the heat set point is more than 3 degrees higher than the current temperature. So I wrote a script that slowly raises the heat point trying to avoid triggering the second stage - but it still comes on.

Does the thermostat trigger it, or does the heat pump itself?

Any help would be appreciated.

JimO.

[jgary]

I have a Honeywell Thermostat (not automated with Zwave etc) at my other house. One programs in the thermostat when they I want the emergency or secondary heat (gas furnance) to come on when the Heat Pump is no longer very effective. So when the temp outside is 40 degrees I have the Heat Pump switch off and the secondary (gas furnance) switch on to heat the house. At one time the temp was set to 35 degrees and I decided to change it to 40 degrees. The thermostat would only allow changes in 5 degree increments.

So to answer your question one programs the thermostat to the temps they want the switch to occur between the Heat Pump and the secondary heat based upon the temp of outside air.

[mterry63]

Another answer:

The thermostat doesn't know the outside temperature, only the current inside temperature and the desired inside temperature.

Normally the difference between these two things is very small (a few degrees) when the system has been cycling for a while.

I believe the heat pump energizes the aux heat once it can no longer recover enough heat from the outside air.

[Rupp]

Yet another answer, the way my upstairs unit works is A.) if the temp on the stat is changed more than 4 degrees above it's current setpoint, the emergency heat kicks in. B.) If my heat pump can't keep up (typically when it's near 32) the emergency heat kicks in.

[sponnath]

I have a TR40 with a Lennox heat pump and 95% furnace.

I run my system as a dual fuel system using Bill Porter's board that handles the switching like you are talking about. Heatpumpmadeeasy.com

I have had extensive conversations with RCS on this. Just emailed with them today. They don't offer a dual fuel thermostat. Running dual fuel is still pretty rare. I think it makes a lot more sense to kill the heat pump at lower temps and just run the furnace. But most still run it as the primary.

You can use a command to send the outdoor temp into your thermostat. Check their command structure. I am trying to find out if the RCS serial plug-in supports this command now on that part of the forum.

You should also check your furnace. There is a dip switch setting in the Lennox that allows it to handle the second stage at about 10 minutes I think. You need to switch that to allow the TR60 to handle the second stage. Otherwise, it ignores the thermostat's signal. Talked to Lennox a lot a while ago. You used to be able to talk to Lennox tech support but lately I have only been able to talk to their schmucky customer service people. About all they can do is barely take your address to send you a pamphlet. HVACTalk.com has been helpful too. Also CadillacKid on the forum here is great on HVAC!

The heatpumpmadeeasy board doesn't allow the thermostat to control the second stage heat. So, I built a relay board that allows the second stage to get to the furnace.

[JimOConnor]

Problem almost solved...

I found that the TR60 has a hidden installers menu with settings that can be adjusted. The settings control when the second stage heat kicks in (along with a lot of other things). I set the relevant ones to "0" which means that they will not be triggered. The second stage heat now comes on after 30 minutes. I think that is triggered by the heatpump.