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Heating, cooling, air quality and hot water advice needed

Mick_McBride | Posted in Green Products and Materials on

Hello All,

I’ve been trying to get our house plans nailed down for many months now, but it has been a long back and forth with our architect. Now that the plans are close to being finalized I wanted to get back to deciding on how to heat, cool, move air and heat water. I haven’t been able to find an online calculator that has the type of house we want to build, poured in place insulated concrete walls with an insulated concrete roof. We’re leaning toward HK Ties for the insulated wall connectors and LiteDeck for the roof. Walls should be around R30 and roof R50. We are located in Boise Idaho.

I have attached part of the plans. All of the ceilings will have soffits that utilities/HVAC can be run/installed. Will probably move Utility room to what is now labeled Pantry so everything is centrally located. Have thought about placing the outside units on the roof above.

1. Heating/Hot water: I have been looking at Sanden SANCOâ‚‚ to provide the DHW and radiant. With concrete floors the thought of radiant heating is appealing.

2. Air Handling: I have talked with Ben at Build Equinox about their CERV unit. I like the system, but the cost might be a no go.

3. Cooling: I really like the idea of using splits for the cooling, but would they be redundant with the radiant heating?

My biggest issue is trying to find someone local to talk to about these things as most all want to push the products they support, Trane, Carrier, etc.

Any advice would be helpful on the above choices or on the house as a whole.

Thank you,

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  1. Expert Member
    Dana Dorsett | | #1

    Before deciding on the heating solution it's important to nail down the actual heat load with a formal (and careful) heat load calculation. ACCA Manual-J method is the "Gold Standard", but for ICF walls and very good site details there may be better simulators out there. Without reasonably good load numbers it's not possible to come up with the most-appropriate solutions, but it's not likely to be a Sanden water heater.

    The Sanden water heater isn't easy to turn into a combi-heater with both reasonable capacity and efficiency. Unlike R410A refrigerant heat pumps, CO2 refrigerant doesn't undergo a phase change from liquid to gas and back during the cycle, and requires a bigger temperature difference to work efficiently and at capacity. To engineer it to work well with a radiant floor is not trivial, not a back-of-the-napkin kind of thing the way it sometimes can be with other water heaters. It also gets cold enough in Boise that if the grid goes down for a day during a cold snap you're likely to suffer freeze damage.

    A more likely bet would be an LG Multi V S with a Hydro Kit. The smallest is a 2-tonner, the largest is 5 tons, and it can simultaneously heat the hydronic zone with the Hydro Kit while running multiple mini-split heads/cassettes in cooling or heating mode. There are a couple different sizes of Hydro Kit in both high temp and low temp flavors. The ARNH-04GK-2 l0w temp Hydro Kit is good for about 47,000 BTU/hr of combined heat & hot water, which should be good enough provided there is enough heat pump behind it (probably a 3 or 4 ton,. maybe a 5 depending on how much heat can be emitted by your radiant design.) For domestic hot water it's best to use a "reverse indirect" water heater (eg TurboMax, Ergo Max, Everhot EA etc) as both the buffer tank for the hydronic heat and the hot water.

    The Multi V "S" was only released in late 2016, but is a scaled down version of their much larger Multi V series commercial VRF systems, but I believe most or all of LG's mini-split heads/cassettes are compatible with it. It's hard to dig up a lot of information on them from LG's websites, and if you can't find a local mechanical contractor in Boise, you might still be able to work with Borst Engineering & Construction in the Medford Oregon area (, which is not exactly next door, but it's not the other side of the country (or planet) either. Gayle Borst would be able to at least point you in the right direction (tell her I sent you), or suggest a more local contractor, even if they can't take on the full design or manage the installation.

    1. Aedi | | #2

      Hi Dana,

      Excellent information as always. You are right in advising Mick away from the Sanden in this case: in addition to the points you make, it makes little sense in a home with a cooling load.

      I am interested in your note on the difficulty in using the Sanden as a combi-heater though, as it is not something I have heard of before. I think I understand the principles involved. A radiant system draws out heat in a slow and steady manner, whereas DHW is quick and intermittent. The Sanden, preferring larger temperature deltas, thrives more with the latter than the former.

      It's an interesting problem for sure, and I am curious as to what the typical solutions are for optimizing it for combination use. Is the Sanden worse than the alternatives for combination use in general, or just more difficult to configure properly? And are there any resources you can point to on optimizing CO2 heat pumps like the Sanden for combination use?

      1. Expert Member
        Dana Dorsett | | #3

        A third party in France designed a reasonably efficient combi solution a few years ago, which Sanden is now marketing in Europe:

        The NEEA and Pacific Northwest National Labs have been testing different combi configuration for several years too:

        See slides on p20 &21 on this presentation of the Eco Runo, but also p.38:

        More of the similar/same:

        The low space heating efficiency and capacity even in the radiant floor application relative to R410A hydronic output reversible chillers and heat pumps is an indication that it's not a simple problem to solve. The EcoCute consortium water heaters and the combi variants thereof have had more than a decade of engineering effort thrown at them. The odds that the average mechanical contractor can even come close to those products and near-products (I don't believe the Eco Runo is available as a product yet) with home-brewed design seems remote.

        That's not to say they can't eventually get there, only that it's premature to think that adapting an ECO2 water heater into a combi is going to be cheap or efficient (it'll probably be neither), or even ADEQUATE for heating this home.

        1. Aedi | | #10

          Thanks for all the information Dana! I was hoping that there was some sort of clever, if complicated, setup that induced high efficiency from CO2 heat pumps in combi application. Looks like we are not even there yet, and all my "clever" homebrew ideas are risky or over-dependent on occupant behavior. It seems these units just are not yet fit for general combination use -- the efficiency penalty is just too high, the only possible exception being a site with unusually high and consistent DHW use.

          The only real solution I could think of is to figure out a way to get the CO2 units to deliver chilled water as well as hot water. I assume that this is impossible for CO2 units, else they would have done that already.

          Thanks again for your expertise.

    2. Mick_McBride | | #9


      I'll look into the LG line up. Have emailed Borst, got a reply and Gayle says thank you.


  2. GBA Editor
    Martin Holladay | | #4

    You are designing an unusual and expensive house -- one that apparently uses concrete sandwich panels for your walls, and a roof assembly consisting of steel ribs, EPS, and concrete. These materials are more typically used at large commercial jobs than on homes.

    Under the circumstances, I'm surprised to learn that you don't want to install a CERV unit because of the cost. If you need to trim the cost of the budget, I can make lots of suggestions -- but this looks like a "cost is no object" type of house.

    If your house will have cooling during the summer, I don't recommend the use of radiant floor heating. Instead, you should probably install an air-source heat pump to handle both heating and cooling.

    1. Expert Member
      Dana Dorsett | | #5

      With the LG Multi V S and something simpler than a CERV for ventilation he can probably have his radiant floor cake and eat it too.

      It'll likely be more expensive than a conventional gas-fired boiler/ water heater for the floor & domestic hot water + split AC, but substantially more efficient and cheaper to run than electric boiler + split AC, possibly cheaper to run than the fossil-burner solution.

      Without load numbers it's hard to narrow it down the most-optimal or most cost effective solution.

    2. Mick_McBride | | #8


      I'm definitely not trying for a "cost is not an object" kind of house. The idea I'm running with and trying to convey to our architect is a very solid shell that we can build out at a later date. I understand the shell will be the greatest expense. Up front, no fancy built in closets, high end appliances, top of the line faucets, tubs, etc.

      However I would like to have the heating, cooling, air handling nailed down as to retrofit those in a concrete house wouldn't be easy. The CERV is an option, but the same amount of money could be used for a multitude of other options.

      I'm putting everything I can into a spreadsheet with costs associated with them as I get them. Soon We're going to have to chose what stays and what goes.

      This is hopefully going to be our long term house, so I want it to be what we want and comfortable.


  3. user-626934 | | #6

    If you're building in/near Boise, you should talk with / hire Skylar Swinford at Energy Systems Consulting.

    1. Mick_McBride | | #7

      John Semmelhack,
      I tried to contact Skylar a while back through his website and he never responded.
      I understand the rush of the industry, but the lack of response of people has been frustrating.


  4. Lebnjay | | #11

    Hello Mick,
    I was wondering what way you ended up going for hvac and radiant.
    We are building a similar home here in Bend, Oregon. ICF walls and floor, cerv/erv, radiant, ductless or ducted minisplits. We have also been looking at and considering some of the same products and would love to hear what worked for you and if you were happy with the result.
    Lebn Lovejoy.

    1. andyfrog | | #12

      Hi Mick and Lebn,

      Did either of you end up going with the CERV? If so, how do you like it?

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