Hi, I have a Waterfurnace and live in a rural area where we sometimes have power outage. I have a back up generator with more than capacity to operate the geo but not with even one of the aux heat banks on. The furnace is wired with compressor and control circuit to one of these aux banks so turning their breakers off will also turn the compressor/controller off. I understand why Waterfurnace does it that way. Can I put a switch in the E (or W) wire to the thermostat to keep the aux heat banks from turning on when using the generator? Thank you!! Mike

Posted By Mike915 on 05 Jan 2018 06:45 PM
Hi, I have a Waterfurnace and live in a rural area where we sometimes have power outage. I have a back up generator with more than capacity to operate the geo but not with even one of the aux heat banks on. The furnace is wired with compressor and control circuit to one of these aux banks so turning their breakers off will also turn the compressor/controller off. I understand why Waterfurnace does it that way. Can I put a switch in the E (or W) wire to the thermostat to keep the aux heat banks from turning on when using the generator? Thank you!! Mike

What model of WF do you have, and is the unit a split or a packaged (all-in-one) unit?

We typically don't use our heat strips, so I have the heat strips disabled via the thermostat installer setup options (Honeywell.)

We have one packaged Envision and one split Envision units and a 20kW generator:

The packaged unit will still run the heat strips due to the internal WF programming during some unit faults (ex. a compressor problem) even though the thermostat doesn't know that heat strips are installed.  We have 15kW (10kW + 5kW) heat strips installed on the packaged unit I believe with a 60 amp breaker on the 10kW heat strip and a 30 amp breaker on the 5kW heat strip.  I leave the 30 amp breaker turned off (for the 5kW heat strip.)

Our split unit heat strips (Carrier air handler) will not turn on the heat strips even if there is a WF fault.

I hope I remembered all of this correctly.  Been a while. 

First of all - Thank you for a quick reply. My apology for taking a week to answer! I'm retired and that should give a lot of free time. I'm working harder now than when I had a job!
My Geo is an all in one, model #NDV049A111CBR.
We live in north central Indiana and our 4 ton heat pump does a great job and only uses the back up heat units (2 stage) when the weather is very cold. Like when it's -10F or more for an extended time. This has been one of those times. Waterfurnace internally connects the control circuitry to one of the heat packs. Reason being if the compressor locks it will trip it's breaker but the breaker that supplies the heat pack will also run the control board. We are lucky to not have many power failures but when they occur power may be out for a while. This unit is about 9 years old and still under warranty for another year. If it remains super cold for a long time the Aux Heat will now turn on. In case of a power failure my generator is rated at 8K and 13K starting. That's more than enough to keep the geo running without the heat packs. It may get a bit colder in the house but at least we will have some heat. Also need to keep our well pump running, a few led lights etc.
None of this is a real emergency but I do not want to do my mod to the furnace while it's under warranty.
I saw a post of someone saying they just disconnected (switched) the Aux heating wire from their thermostat and that alone will keep the aux heat off. Sounds likely true but wanted to get some other opinions first. Ice here today - I may get a chance to test it!
Thank you again for your help!

What HP is your well pump? Do you have a soft starter on your heat pump? Have you tested your generator to verify it will start your well pump and heat pump? A 4 ton heat pump compressor without a soft starter will have starting current up in the 75 to 100 Amp range at 240V (>18K). Check your unit nameplate for Locked Rotor Current (LRC) to see how many amps it can pull during unit startup.

If you have staged heat strips with a 5kW heat strip on the same breaker as the fan and a larger second stage of heat strips on a second breaker, it might be better to plan on just running the first stage heat strips when on the generator rather than the heat pump (put the thermostat into emergency heat mode and open the breaker to the second larger bank of heat strips).

Mike, was you able to get the generator to run your Waterfurnace? If so, what was required? I’m now in the same process, have a portable 12.5 KW gen and thinking (wanting) to run WF. Thanks!