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What Size Breaker for 8kw Heat Strip? – An Expert’s Guide

Written by Edwin Jones / Fact checked by Andrew Wright

what size breaker for 8kw heat strip

I’ve had a couple of homeowners ask me, “What size breaker for 8kW heat strip?” I always say that you need to consult the manufacturer’s booklet. Certain heat strip kits require their own circuit and, often, have different max overcurrent protection.

With that in mind, while the minimum, correct size may be 40 amps for most strips, that doesn’t mean other breaker sizes like 45 amps and 60 amps won’t work with them. Don’t forget to consider the available CB models, too. Read on for more details.

Why It’s Important to Stick to Manufacturer’s Recommendations


You can confirm what I said above with these specific kits produced by MrCool and Goodman. The former needs 45 amps, while the Goodman 8kW heat strip requires a 60 amp breaker – all provided by the manufacturer.

Most of these products are 240 volts instead of 120 volts. Looking at the booklet, assuming it’s available, would save you all the trouble of figuring out the right size.

At the same time, knowing the voltage is crucial, since a slight difference can affect the required size. For example, a 8kW heat strip at 240 volts will demand a 45-amp breaker, while the same heat strip that comes at 208 volts would need a 40-amp one.

You may be thinking: But if we do some calculations to convert 8kW to amps (i.e. Total Amps = Watts divided by Volts), shouldn’t a 240V strip use 33.3333 amps only, and would, therefore, need only a 35-amp or 40-amp breaker instead of a 45A one?

Again, this highlights the importance of your air handling unit’s electrical setup and recommendations.

Is it being served by a single circuit? This is common among many kits. If so, take note that other features and components add to the total amps. These include the:

  • Blower motor
  • Controller, control panel, or other control features

With that in mind, heat strip sizing can only ever be 100% done correctly by referring to your air handler’s manual. If you somehow lost the physical copy, you may find a digital one online by visiting the manufacturer’s official website.

Most of these manuals contain detailed tables that outline the required breaker sizes, wire sizes, and power draw of the heaters.

You’ll also learn whether aluminum wire or copper wire is recommended. There’s no better reference for this exact information than what the manufacturer advises.

Take Note of Circuit Breaker Size Availability, Too

You may have to go for a larger or smaller breaker than what’s recommended. For instance, there are different circuit breaker manufacturers that don’t offer 45-amp breakers.

Siemens is the first brand that I can remember not offering it. What if you have a 7.5 kW heat strip breaker size of 45 amps? Well, you have to choose a higher 50-amp one instead to remain code-compliant.

It’s all good if your available size wire also accommodates the size upgrade. If not, you have no other option but to make sure that the wire size matches the breaker size.

How Do I Know What Size Heat Strips I Need?


Leaving aside this talk about the breaker size for an 8kW heat strip, let’s discuss something that’s, more or less, relevant to it. Do you really need an 8kW heat strip to fulfill your property’s heating requirements?

After all, many homeowners make the mistake of overshooting or falling short of what they need, resulting in unbearable heat or teeth-chattering cold, depending on the weather they’re up against.

Consider these factors first:

  • Climate
  • Window size and position
  • The home’s heat needs
  • Heat pump’s size
  • The pump’s maximum potential heat loss

Most will recommend sizing heat strips to a minimum of 70% or 80% of the pump’s heating capability. That’s all well and good, but it won’t hurt to measure the exact BTU (British Thermal Unit) your room needs and the heat strip’s own BTU to be sure.

8kW comes to more than 27,000 BTUs. In both air-conditioning and heat pump systems, that amount serves a room that spans 1,350 square feet. That’s 27,000 extra BTUs delivered, not including what your heat pump can already give out.

After you become sure of your property’s exact BTU requirements, you should also take note of some heat pump units being rated down (i.e. performing less optimally) once the temperature reaches a certain point. Take the following scenario for example:

Let’s say you have a 10.5kW heat pump that rates down once the temperature hits 17 degrees. Normally, let’s assume it will deliver 36,000 BTUs at an ideal 47 degrees. When the ambient air is 17 degrees, however, the total BTUs it can give out may dip to 18,000.

Such scenarios happen, so you will need an additional 18,000 BTUs to offset the heat loss. If you’re well aware that such extreme dips happen in your locale regularly, then it’s worth being extra careful with the heat strip size you’re using.


As you can see, there’s no set answer to the question, “What size breaker for 8kW heat strip?” Most brands design their HVAC systems differently, and heat pumps and air handling units, along with their integrated heat strips are no exemption.

Don’t depart from the AHU breaker size manufacturers recommend. More importantly, make sure that your property will be able to get all its heating needs by using the correct heat strip size.

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