Testing Emergency Heat

Many homes in my area are heated and cooled with a heat pump. I like to test the heating in heat pump mode, being careful not to set the thermostat more than a degree higher than ambient. Then, I try to get emergency/backup heat to come on, either by cranking the stat 10 degrees higher than the room, or by using the manual emergency heat switch.

Usually, the temperature differential in heat pump mode is between 16 and the mid or high 20 degree range. Backup heat seems to be greater than the mid 30s and is generally obvious because it feels and smells like a hair dryer.

Lately, though, a whole bunch of systems I’ve encountered are outputting the same temperature differential in emergency heat as in heat pump mode, and I’ve flagged those as defective.

Is there something wrong in my approach here? Are some of these systems smart enough to lock out emergency heat if the outside temperature is warm enough (say, 40 degrees F) or if the heat pump is working normally? Or are over 60% of systems just incorrectly wired?

Do you observe the condensing unit while in EM mode? Is it operating?
Do you do an AMP draw on the heat strips to see if their energized in EM mode?

A smaller heat strip kit (5kw instead of 10kw) will give a lower temperature.

Mis-wired T-stats are very common around here, resulting in odd operation of Heat & Emergency Heat, etc. Often find the A/C operating while in EM mode too.

No, I don’t typically check the condensing unit when doing this test. Some, like mine at home, are wired to keep operating in parallel with the heat strips. Others lock out. Really doesn’t tell you anything. Every heat pump I’ve ever had continues running, no matter how cold, with or without backup heat active. Makes little sense, really.

I do not measure currents. My opinion is doing that is far outside the SOP. In some cases that would require opening the air handler. However, a clamp-type ammeter could be used…never thought of that. I could try doing that. But it still would require a bunch of extra running back and forth.

Todd, you mentioned that measuring currents is outside the SOP. I’m wondering if the emergency heat testing that you are describing is also outside the SOP?

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I don’t think it is. Where does one draw the line? Turn on the heat and see if it feels comfy inside? I measure the temperature difference between ambient (at the stat) and one of the registers. I attempt to measure, non-invasively, all operating modes available to the user. This gets tricky when there is a multi-stage system involved, as it can be difficult or impossible to test the stages using just the stat as a control.

I’d be upset, as a client, to suffer through a cold house on an exceptionally cold night only to find out the backup heat doesn’t work and the inspector missed it. It’s a rare occurrence in our area to be so cold that the heat pump can’t keep up, but it does happen…especially with lower-HSPF/SEER models.

I’m just finding so many systems where the backup heat doesn’t appear to work that I’m questioning my methods, and wondering if these systems have more smarts than I expected. I assume that commanding emergency heat or setting the stat really high should force the heat strips to come on. I did find one gas-backup system that refused to fire the gas when the outdoor temp is warm, but the HO verified that the gas heat works. Go figure.

This subject used to be one of my pet peeves when I was in the business. There is only one way to know if all the heat strips are operating and most HI’s always jump on on its out of the SOP to use a clamp on amp meter. How in the hell is one to know when there are multiple strips that all are operating unless you check each one with a meter. Three to four elements (strips) are most common and they are not always in use are the same time. The first element in the series is the most heavily used and is usually the one that fails first. These elements are staged on and one must jack the stat up high enough to make the second stage elements activate.