GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Air-Source Heat Pump Heat Strips

pdxcoug | Posted in Mechanicals on

Building a home in Zone 6B (cold and dry), and installing a Daikin VRV Life electric air source heat pump, which is rated to -4F. I noticed a line item on my HVAC pricing for $1284 to install heat strips. I questioned why they are needed and the response was, esoterically, that it’s something to do with Manual J calculations.

My state operates off 2018 IMC and mechanical sections of the 2018 IRC. I searched both codes and can’t locate this requirement. We’re installing a wood stove; if the heat pump fails in the wintertime for any reason – pump, refrigerant, power failure, etc. – we’ll have a fire going. Honestly we’ll probably have a fire going a lot of the winter regardless.

Electric heat strips don’t work if the power goes out, they only kick in when the heat pump fails for some other reason. And when they do kick in they use a lot more electricity than the heat pump. I’ve also read on this site that they can kick in by mistake, which is concerning.

My question is: what is there in the Manual J process where backup heat, and backup heat that doesn’t factor in the wood stove, becomes a requirement?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. paul_wiedefeld | | #1

    I think they're implying that at some outdoor temperatures the heat loss > heat pump capacity based on the manual J. So adding in the electric resistance + heat pump >= heat loss at those temperatures. I understand the conservative instincts of the installer and think installing the heat strips is a fine idea, as long as they aren't really oversized is a safe backup. You're correct, they won't work when the power is out. They'll be wired directly, so you can flip them off at the panel so they don't accidently turn on but keeping them energized could be helpful with defrost cycles. Another benefit is reheat for cooling - sometimes the latent load is high but the sensible load is not, so to dehumidify some heat pumps will run the AC then use the resistance backup to warm up the air slightly to prevent the house from cooling too much.

  2. Expert Member
    BILL WICHERS | | #2

    The usual requirement for electric heat strips is to provide a "backup" source of heat that is still automatically controlled. It's usually insurance companies that require this, maybe a few municipalities too (I usually hear about it as an insurance requirement). The insurance companies won't let your wood stove count because you have to tend it -- it can't run automatically. All the insurance companies really care about is protecting the asset securing your mortgage, so they don't want freeze problems if you're away. People who heat with wood boilers as a primary heat source often run into the same issue.

    A heat pump with electric auxillary heat for extra cold days should satisfy any "you can't just rely on a heat pump" people too. It's not a bad idea to have a few electric heat strips for those ocassional polar vortex days though. You can always just shut them off when you don't need them, or use a simple line voltage thermostat to control them. Line voltage thermostats are very simple devices and tend to be very reliable as a result.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |