Electric Heat Troubleshooting, Service, and Math Class

In this class Bryan teaches the Kalos technicians Electric Heat Troubleshooting, Service, and Math. This includes electric heat, often used supplementary in heat pumps and furnaces. He also shares stories from the field.

Heat strips are one form of electric heat. It would stand to reason that taking a bit of heat strip off wouldn't hurt anything, but the electric heat would be less effective. However, when you factor Ohm's law into the equation, you'd be taking off part of the heat strip and reducing the resistance, meaning that the amps will increase. Heat strips also burn out when they touch another piece of metal, like the casing around it, as the amp draw becomes much higher.

Electric heat has some benefits, including its consistent BTU output (3.41 BTUs per watt); regardless of the outdoor temperature, you can expect the same BTU output all the time. It is also reliable and usually easy to work on. However, it is inefficient. Electric heat is the baseline of COP (coefficient of performance), and a pool heat pump that has a COP of 3 is three times more efficient than just the electric heat.

Electric heat has other issues, including odors or smoke when it first starts after a long time of inactivity. (It's easy to burn off the heat strips on a PM, especially if you jumper W to R or use the thermostat to burn off the heat strips.) Electric heat also causes high bills when it runs too much and causes stress on the electrical service. Electric heat elements also draw very high current, so you have to manage your wire sizing and electrical connections. You can also encounter mistakes with blower interlock; you don't want to run the heat strips without the blower running.

In a 4.6-kilowatt (5kW) heater, you would divide 4,600 by the unit's rated voltage to get the amps of electric heat. The wattage decreases when the voltage decreases because of Watt's law. When you put more voltage (electrical pressure) on the circuit, you get more current. So, the total watts would decrease if volts or amps were to decrease. If you divide the watts by voltage, you can find out your amps. To find the BTU output, take the watts (volts x amps) and multiply them by 3.41. You can also use Ohm's law to find the resistance. Take the voltage and divide it by the amps to get the resistance (ohms). The voltage is a moving target, but resistance stays constant for the most part.

The data tag should tell you the proper wire size to feed the air handler; look for the MCA (minimum circuit ampacity) to help you make your decision. Keep in mind that 5-kW heaters are not necessarily 5 kilowatts.

When it comes to terminals, you have W, W1, W2, W3, and E. W is just heat; it is usually just for a single stage of heat. W1 means first-stage heat; it indicates the compressor with the reversing valve de-energized. W2 means second-stage heat and can refer to electric heat. W3 is the next stage of heat, and E is just for emergency heat. We used to have to jumper Y1 and W1 and a few other terminals together on older thermostats; they perform similar functions, but the reversing valve would distinguish heating from cooling.

When testing heat strips, you can usually (but not always) expect 5kW heaters to draw 20 amps and 10kW to draw 40 amps but still 20 amps per strip. However, the way you read the amps can change based on the voltage (230v vs. 208v). Commercial buildings often have 208 volts supplied to them because they are hooked up to two of three power legs.

Heat strips also have thermal limits; therm-o-discs can be found on the high and low sides for extra protection. These discs also have temperature ratings on them. You can tell if the thermal limits are open by ohming them. If they are open, you'll measure OL or infinite ohms. If they are closed, the ohms will be low.

To control the electric heat, a unit will have either a contactor or a sequencing relay. Sequencers have contacts that close at different times. You don't want to use a 90-340 relay, but we sometimes use those for a fan interlock.

When using a 90-340 for the fan interlock, you must set it up correctly as not to melt the relay; the current from the heat strips should not go through the relay at all. To avoid confusion as much as possible, follow the wiring diagram and think of the relay as upside down.

We can also stage heat strips if we have more than one. Staging makes the unit draw lower inrush current and use less electric heat (the less you use, the better).

When testing heat strips, you can use three methods: measure the heat strip amps, test on and test off, and force the system into defrost to test the heat strip amps.

Heat pumps with supplementary heat may have special code considerations when wiring to the outdoor thermostat, which you must keep in mind.

[drclemthesim]

Aonther reason I love hvac school your stories add some dad jokes next time lol

[strongocho]

I regret not going to a trade school. I used my GI bill to go to college and get a useless degree that put me in a cubicle for the past 10 years, and here I am at 35 watching youtube videos and hunting for an apprenticeship to replace the trade school I should have gone to in the first place. These videos are a HUGE help to get me ready though, and there are things about this style of learning that are not all that bad. I can pause this lecture several times to take sidebar research and clarify things he brings up that may be a term I don't know or concept I am not familiar with yet, whereas in the classroom I just have to make a not to look something up later.

[TotalAirCareServices]

I respect the fact that you admit to your past mistakes. Lot's of seasoned techs pretend they have never made a mistake to the newer techs.. Good deal!!!!

[aaronclark]

This guy is good and he's such a great teacher I've been doing HVAC for 20 years and this guy still always teaches me something

[TheSuper]

Man this brought back some many cool memories… Having a laid back / chill teacher is what makes this trade the best. Learning and having a laugh here and there is what I looked forward in class in my days of learning. I notice early there was never a dumb question because it always had an answer lol.

[vindictii]

I'm not an HVAC tech, i just like to watch random classes on Wednesday nights. Great show!

[AVIIDIX]

Im completing electrical engineering programs in school right now and these lessons are way better to learn and understand what's actually going on. Great lessons keep up the great work!

[jericosha]

Thank you so much for sharing these and willing to be vulnerable. You guys are a blessing to techs that are seeking to better themselves.

[cowboyfrankspersonalvideos]

WOW! Your video is the first time in 50 years I have seen ohm's and watt's law displayed in the circle format in the way I learned way back in the late 1960's. You're even using the letters I learned. I've always had difficulty in remembering the formulas as written. The circle form I can see in my head. Good job. I think that is the easiest way to remember them.

[mikechiodetti]

I happened on to this class. Before retirement, I was an automotive electrician with auto/truck HVAC experience. This class is great for commercial HVAC, and some of it makes sense to me. I would need to obviously go through the beginning or entry level training to understand the whole picture.

[winstagram]

Your slide about W, W1, W2, W3, E is the best explanation I’ve seen. I live in Houston and even thought it’s prime climate for heat pumps they are extremely rare. With all this electrification shit coming out we’re trying to start pushing them to be ahead of the curve. Well, my first install with a Honeywell T6 thermostat kicked my ass trying to figure out what terminals to use. This would have saved me a lot of frustration! Thanks!

[pl]

You also need to add the amperage of the blower motor to the supply of your heat strips since it will be powering both of them. It will also be an inductive load unlike the heat strips so it will draw more amperage than usual when first turned on.

[workinprogress]

Love your lessons, Bryan. Would be great to see ways to test voltage in the ciruit. What you read on each side/across relays when they break one or both legs of power, etc.

[bkoz]

I love the honesty, we've all been there, made mistakes, learning process.

[borshardsd]

I think the math used to figure out factory specifics for resistance is vital.

I am working on an old univent and will be using some info from here.

Alway great content!

[frankroper]

It's good to know the ohms of what you are working on since you can't always jump red to white...the reason is in some old buildings they have used whatever color wire they had on hand to wire a thermostat and you have to know the ohms of what you are working on and then ohm out the circuit to the common wire until you find the right circuit. It is not a perfect world like in a classroom when you get out in public! They jump stuff and then you have go in and try to figure what they did so you can get to the root cause to begin with.

[skyplie]

Great man Love your training method !!!! going to take some classes and i watch your videos for i go take school. So that I'm not completely lost.... awesome keep up the good work.

[brianmcdermott]

Great class Bryan. Thanks for your time.

[smokeysmith]

As a courtesy thermostat heating adjustment at a sister building, who’s heating elements were packed with dirt, I emptied out a four story office building when energizing the heater contactor.

[jonathanschulz]

I don’t like using the word “inefficient” for electric heat. It’s actually 100% efficient, buts not very cost effective because the “fuel” (electricity) is more expensive than gas. Buildings downtown actually qualify for being “green” if they have electric heat because of its efficiency rating. This can be confusing as your heat pump can produce more btus than running electricity through heater but they use the same “fuel”. As a tech who does not work on a lot of air heat pumps, I wonder at what point, if there is one, in which elec heaters vs gas vs heat pump is more effective at BTU output. So I wish there was a more clear way of explaining this. It’s more about cost effectiveness. A class on this topic would be cool. This was a great class though.