GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X 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

Hydro coil with Mitsubishi heat pump

joe_fb | Posted in Mechanicals on

We are considering a ducted mitsubishi heat pump system (SUZ/SVZ). We have existing hydronic baseboard heat via oil that we would abandon.

A suggestion has been to add a hydro coil (aquecoil?) to the air handler to deliver heat on the colder days using the existing boiler.

Two questions I need help with…

How does the aquecoil heat feel in this situation – classic furnace on/off or does it modulate like the heat pump?

In case of a power outage, could we run just the air handler and boiler off a (dirty power) portable generator? Or does the heat pump outdoor unit with all the smarts need to be powered as well? 

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 have the hyper heat version of that setup. Unless you’re in the -10 F and colder range or are pushing past the capacity, you won’t need that. If you do need backup, why not just keep the baseboard? That’ll be use less electricity in the generator scenario.

    If you want an incorporated backup, Mitsubishi makes this:

    1. joe_fb | | #2

      If we left the baseboard, as I understand it, we'd have to switch to the boiler at 32 deg or so to prevent the pipes from freezing in outside walls. Or we'd have to put antifreeze in the pipes which I'd like to avoid.
      If we did a hydrocoil we could drain the baseboards and have nothing in the outside walls to worry about freezing.

      To my question: what's the heat like from the hydrocoil? Is it a blast on and off?

      1. paul_wiedefeld | | #3

        Depends on the hydro coil and the controls - there are third party air handlers that modulate blowers for heat pumps and hydro coils, I’m not sure if the intelliheat can do it. I think the SVZ can modulate blower speed for electric resistance. For what it’s worth, the SVZ indoor unit doesn’t really modulate in practice if the indoor set point is kept consistent. The default always seems to be low speed fan.

        For an oil boiler, you’ll need something to buffer the load if you don’t want an short on-long off cycle. Even if the blower can modulate, the boiler cannot. Sticking a buffer tank in between the two would address that. With enough effort, you could supply a temp and amount of water such that a constant speed blower could run continuously, which would actually exceed the heat pumps turn down capabilities.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |