Great suggestion. Thank you.
Great suggestion. Thank you.

Jody, I’ve not personally
Jody, I’ve not personally seen a 15kw heater that was staged in 3 5kw stages. All I have seen are staged 5kw and 10kw. When I run into a 15kw heater that is operating from a single stage aux. stat, and the heat loss of the house doesn’t require more than 10kw, I will suggest having the heaters operated at the 10KW from the indoor thermostat and have the outdoor HP defrost control operate the 5kw stage. This saves energy during defrost.

Thank you Robin, I didn’t
Thank you Robin, I didn’t think about the 3rd party heaters being mostly the same. This does line up with my idea and hopes that aux could stage 5>5>5Kw. Yes, I’m getting a better understanding of this part of the systems with these conversations. Options for less energy consumption is my specific issue. Thanks for your help.

That pretty much covers it.
That pretty much covers it. Now just manufacture specific I can dig into. Thank you David, I appreciate your time and knowledge. Great education for me.

@Jody, too many different t
@Jody, too many different t’stat models to make generalizations. Keep in mind that if marketing literature says ‘multi-stage heat pump,’ that refers to compressor stages (Y1/Y2) not aux heater stages (W1/W2). You have to check the wiring diagram to see if the t’stat terminal strip includes W1/W2. I don’t recall seeing a thermostat with more than two aux heat stages.

If the heater kit has 3 stages, it may be possible to field-wire the first stage to W1 and last two stages to W2 while preserving sequencer staging between the 2nd and 3rd steps. BTW, sequencer staging is accomplished with bi-metal switches that react to heat within the switch itself and the delay is indeterminate and relatively short in duration – on the order of a few minutes. As I said, sequencers are primarily for mitigating grid loading.

Instead of staging the aux heater, you could have a tech simply disable the 2nd stage. You’re likely to find that you never need it. In my experience, aux heater kits are usually grossly oversized. It’s common practice to size heater kits based on a home’s peak heat load in case the heat pump fails. Not only that, the calculated heat load always overstates the true heat load. The largest kit I’ve specified in the last decade is 8kW. You can’t stage kits that size.

Variable speed ‘communicating’ heat pump systems must be paired with the proprietary wall control to get full benefit of all the features, but these systems usually have additional built-in options regarding aux heater control. Each brand/system has its own features so generalities cannot be made. From a controls standpoint, there’s no difference between small tonnage heat pumps and the largest capacity models. That said, the large multi-step kits can’t be used with the smallest air handlers since they don’t move enough air to maintain a safe delta-T.

Since most manufacturers of
Since most manufacturers of HVAC equipment use third party heaters, they are all basically the same. They all have staged heating over 10KW. It is a matter of whether or not the controls being used are designed to handle the staging. Those controls will always be the main thermostat, but could also be outside temperature thermostats. For instance, auxiliary heat on a 15kw system could be set up with the main thermostat only bringing on 5kw of auxiliary heat unless the outside temperatures drop below a preset temperature, when all 15kw would be energized, still sequenced to come on as 5kw at first, then the other 10kw kicking in a few minutes later. There are many ways of setting up auxiliary heat with the use of temperature controls including, but not limited to main thermostat, outside temperature thermostat and/or leaving air temperature sensor.
What is the specific issue you are looking to resolve?

Good to hear all these
Good to hear all these options at the stat, Endless almost. To variety one would have to take the system apart if they were not monitoring it at the box, correct? I would hope that the outdoor temps and system COP would be the major indicators for newer system to revert to aux. Or is that with only VS or the higher end products? Thanks, Appreciate your comments.

Thank you David,
Thank you David,
This was informative. Do most or all the modern multi stage t’stats have more than 2 terminal to handle larger systems aux set ups? If it is limited to 2 stages and the system starts with 10Kw then the next call would trigger the other 10Kw, correct? Do the new variable speed heat pumps and air handlers systems have better capability at larger tonnage? Or are they so proprietary you have no control? Thanks

@Jody, not unlike
@Jody, not unlike conventional electric furnaces of yesteryear, aux heat staging is a function of the particular brand/model of the electric heater kit and air handler, not the heat pump. Only the larger heater kits are staged. For example, Carrier heater kits up to 10kW are single stage, above 10kW are staged. Lennox kits up to 8kW are single stage, above 8kW are staged. The largest kits (typically 20kW for residential) may have as many as 4 stages depending on brand/model.

In most cases, staging is managed by a “sequencer” integrated with the electric heater kit itself. The idea is to avoid hitting the grid with such a a large amperage all at once. Some multi-stage heater kits can be field wired so that staging is controlled by the thermostat, however, this requires a t’stat that supports multi-stage aux heat, typically indicated by terminals marked W1, W2, etc.

While every system can be
While every system can be different when it comes to how auxiliary heat is staged, the most common method is that the thermostat will call for auxiliary heat when the temperature drops below the targeted temperature due to the heat pump not being able to keep up. At that point, in most cases, the relay for all electric heat coils is activated, but, time delay relays may only allow so much of the auxiliary heat to energize immediately in order to lessen issues from a power surge. If your thermostat has more than one auxiliary heat mode, and if the auxiliary heating elements are wired for staging, then only a portion of the electric heat will turn on when the temperature at the thermostat falls below the setpoint, and more electric heat strips will be energized if the temperature continues to drop.
Auxiliary electric heat is also energized by the heat pump’s defrost control when the heat pump goes into defrost. Again, it depends on the type of heater strips you have and if they are wired to be staged. I always set up the defrost auxiliary heat control to only energize the smallest electric heating element, if I utilize the auxiliary heat feature for defrost at all.