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  1. paul_wiedefeld | | #1

    I don't think an air-to-water is economical at all for this situation. Hydronics gets incredibly uneconomic at small scale. You'll need a buffer tank, circulators, valves, an expansion tank, a manifold, possibly a heat exchanger, a dirt/air separator, 1000 feet of pex, etc. The physical footprint alone is challenging in a house of this square footage. This is all before the heat pump itself.

    The Sanden itself is expensive and extremely niche in the US, as are all air-to-water systems here. Should anything go wrong with the system, you'd probably be starting over. Its warranty when used for space heating is only 5 years I believe. It also sends potable water outside, so everything must go right for it not to freeze.

    What's the heat loss for this proposed building? Assuming it's around the Sanden's heating output (only 8k Btu/h) and AC isn't important, 3 minisplits are overkill and would perform poorly. If ducted is ruled out, then 1 unit in the main room and electric baseboard in the bedrooms is probably the easiest path. Use an electric tank for the water heating and solar to wipe out the bill. A single ductless unit will be incredibly efficient and the entire setup should come in <$10k.

  2. Expert Member
    NICK KEENAN | | #2

    Are you going to build this house or just design it? Because we can get a little more outlandish if it's just a design project.

    One of the issues with mini-splits is that the smallest heads available are about 6000 BTU/hr. So if you need three heads that's 18K, which sounds like a lot for a well-insulated 800 SF house. And oversized units tend not to be efficient.

    Have you looked at the Chiltrix air-to-water heat pumps? They sell hydronic heads that basically look like minisplit heads but the medium is water instead of refrigerant. But the smallest head is rated at 3,000 BTU/hr. You can also derate them by running at a lower water temperature, which actually makes them more efficient.

    They offer a domestic hot water option but I think it's kind of hokey.

    Pricing is here:

    1. paul_wiedefeld | | #3

      I really want air to water to work, there could be so many benefits. That said- the chiltrix FOB price in VA for the outdoor unit alone is $4700 and their buffer tank is $1000. I assume both are pre-tax. Probably an installation of ~$15k? I’ve been quoted <$4k for a wall mounted Mitsubishi hyper heat system (9k btu) installed. Until something changes in the US I couldn’t in good conscience recommend air to water.

      1. Expert Member
        NICK KEENAN | | #4

        Pretty much why I asked if this is just a design project or will actually get built.

        1. paul_wiedefeld | | #5

          Yeah I understood your point and we’re on the same page. Since this question gets asked nearly everyday, I want to make sure it’s clear for others.
          That said, I think there’s a connection between bad designs and projects that never get built. Putting expensive equipment from a minor manufacturer in a house that size definitely makes it less likely it’ll be constructed.

  3. mleelman | | #6

    Hello All, owner working with a GC and doing tons of HVAC research here.

    We're planning a small (about 500 sqft) A-frame build in norther VT (climate zone 6) and are weighing different HVAC options. Our goal is to be a fully electric net-zero with the help of groundmounted solar (unfortunately the building site has tons of shading from the south). Our design calls for an insulated crawlspace foundation. We're aiming for R-40 to R-60 in the roof/walls (its an Aframe they're the same thing) with 1ACH50 airtightness (Pretty good house). We also want to run a hot-tub as efficiently as possible and will need air conditioning in the summer.

    It makes a ton of sense that hydronic heating and cooling systems are overkill for small well insualted and sealed homes. My question is how different would the total system costs be of these two ideas:

    1) An air-to-water heat pump with buffer tank and seperate hot water storage tank with backup coil (for DHW) to provide for all systems; heating, DWH, hot-tub. Looking into ceiling panels such as ThermalBoard. We are thinking we would want an HRV system no matter what, and are wondering the extra cost of including a dehumidificaiton system so that we could utilze the hydronic system for cooling as well and not need to worry about condensation. In my mind, this system would use less total energy and would help to downsize the PV array needed to reach net-zero.

    2) Mini-split heat pump for heating and cooling. Electric on demand hot water for DHW. Seperate hot water heater for the hot-tub. Still using an HRV for air quality although we wouldn't need a dehumidificaiton system.

    My thought is that the resistive heating for the DHW and hot-tub would require a larger PV array and that the total system costs above might be similar. Does anyone have any insight into the cost / feasibility of these two system ideas?

  4. paul_wiedefeld | | #7

    My wall mounted minisplit price experience was ~$3k for a small Mitsubishi hyper heat, $4.5k for the floor mounted version. It took less than a day to get professionally installed. Air to water might be 5-10x that cost? Hard to say, these are so uncommon.

    Is this a year round occupied house? Does the utility offer a green energy option?

    1. mleelman | | #8

      Paul, you're right heat pump powered hydronic heating and cooling is rare around here and its been a struggle to find information on the matter. It is quite clear that for just heating and cooling, its hard to beat a mini-split system. However, there are a handful of benefits to air-to-water heat pumps hydronic heating and cooling (silent, doesn't take up wall/floor space, very efficient) that I really want to do my research to find out if its feasible. The edge case of using the same system for everything (heating, cooling, DHW, and hot-tub) is what makes me think that the upfront costs might not be too different.

      This will be a year round occupied house and it turns out Green Mountain Power has .03$/kwh option for renewable energy witha plan to be fully renewable for all customers by 2030. This could take the need for residentail PV out of the equation.

  5. paul_wiedefeld | | #9

    I’d read the Idronics journals from Caleffi, they’re incredible resources. The hot tub is the wildcard from my perspective, I think the other DHW can be handled by a tank resistance/tank heat pump for a fraction of the upfront cost. An air to water heat pump will actually be less efficient at heating and cooling compared to air-to-air central heating/cooling. I’d avoid the tankless electric if you can find space for a tank, which you seem to be able to since the A2W option had two tanks. I think one-to-one ductless unit + resistance tank might come in around $5k, so you’d have to save a ton on DHW + hot tub to make it pencil.

    This is one of the downsides of Hydronics, for all of its positives, Americans have rejected it for the most part.

    1. Expert Member
      DCcontrarian | | #12

      "An air to water heat pump will actually be less efficient at heating and cooling compared to air-to-air central heating/cooling."

      Do you have a citation for that? The air-to-water manufacturers claim otherwise.

      1. paul_wiedefeld | | #13

        Just the specs themselves. It makes sense - air->refrigerant->water-> air seems more complicated. Plus return air temps that are lower are going to transfer heat better.

        Distribution energy should be lower with water, but people screw that up all the time.

  6. Tim_O | | #10

    There is a new player on the market by MbTek called the Apollo heat pump. They are a bit less expensive (and their peripherals are also less expensive) than the names who have been around for a few years. For what you are wanting to do, it might work out to be not a huge premium. Arctic Heat also offers their cold temp pool/spa heat pump that might do what you need 10-11 months out of the year for only $2k (before import tariff).

    Apollo 3.5 Ton HP, 14 gal buffer tank, Fan Coil unit, and their pump station comes in at ~$6200. The pump station may be over priced at $1500. It includes the controller, pump, expansion tank, and back up resistance. Install of that system shouldn't be too expensive I would think. Maybe $8000 all in? That cost difference might start to pay off relative to resistance pretty quick.

    Almost all the A2W heat pumps on the market are rebadged units from China, and subject to a large tariff, which doesn't help the pricing issue.

  7. Expert Member
    Akos | | #11

    The only way to do anything hydronic at a reasonable cost is if you can DIY. As soon as you say anything hydronic, you are starting at $20k price tag before equipment. Hard to justify that cost, even if slightly more efficient way to heat your hot tub, ROI is never.

    DIY is a different story, it can be made to work, just not sure the effort is worth it for a 1000sqft. Hydronic only really starts to make sense for very large homes where you have very different heat and cooling demands in different areas. Many moons ago I did hydronic heat + mini splits for my home, if I could go back in time, I would simply install a ducted mini split and call it a day.

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