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Q&A Spotlight

Hedging Bets on a Heating and Cooling System

Does it make sense to Install both a hydronic heat system and a heat pump for AC?

Under construction in Maine, this house still needs a firm plan for a heating and cooling system. The owner is tentatively planning both a radiant floor distribution system and a heat pump for air conditioning. Photo courtesy of Brenton.

Brenton is building a new house in southern Maine (Climate Zone 6) that he currently plans to insulate with a combination of open- and closed-cell spray foam plus a continuous layer of exterior insulation in the form of R-6 Zip R-sheathing.

He’s willing to take suggestions on that approach, as he explains in this Q&A post, but a more pressing concern is how to heat and cool the house.

“I have been planning on installing a hydronic radiant system throughout the whole house with a wall hung Viessmann Vitodens 100 propane boiler,” Brenton writes. “My wife would like ac for the humid summer months here in Maine so I’ve been considering adding a 5 zone Fujitsu air sourced heat pump.”

“My question is this,” he continues, “would I be better off going solely with heat pumps for my heat and ac and scratch the radiant and put that money into solar? Or should I install the radiant and have the heat pumps for ac and auxiliary heat?”

That’s where we begin this Q&A Spotlight.

First, review your insulation plan

Before discussing heating and cooling, GBA Editor Brian Pontolilo suggests Brenton take a second look at his plans for spray-foam insulation, particularly in the roof where Brenton is planning to use 11 inches of open-cell foam.

“Because you weren’t specific about the roof and venting, I want to point out that when using open cell spray foam in the roof, the assembly should be vented,” Pontolilo says. “Closed-cell spray foam is the only reliable option for beneath the roof deck in an unvented assembly.”

A second option for an unvented roof would be to install rigid foam over the roof deck, which would allow Brenton to use a number of insulation types below the sheathing.

As to…

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4 Comments

  1. Brian Just | | #1

    You might want to think further about the multi-zone heat pump. There are a few studies out there pointing to significant efficiency hit with that equipment vs. 1/1s.

    1. Expert Member
      Dana Dorsett | | #2

      +1!

      A 5 zone single compressor heat pump is usually going to be sub-optimally (even CRAZY) oversized for a 1300' code-min or better house, leading to poor latent cooling control and low efficiency short-cycling. A zone per floor using ducted (or ductless- in open floor plan) mini-splits would allow proper sizing, for higher efficiency.

      Spending the $20K allotted to the hydronic system on rooftop PV would more than cover the space heating/cooling expenses.

  2. Expert Member
    Carl Seville | | #3

    Does anyone find it concerning that an already framed house doesn't have a mechanical system figured out in advance?

    1. Christine & Pete | | #4

      My thought as well. We are still trying to figure our systems out and our house is only on paper.

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