Sub Floor heating

Discussion in 'Multihulls' started by saltifinch, Apr 1, 2016.

  1. saltifinch
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    saltifinch Junior Member

    I've been trying to think of an efficient way to heat a catamaran, and I feel like sub floor heating must be the best idea. It's proven to be more efficient and effective in houses,. I hate air blowers, and I feel the design of a catamaran makes moving hot air very difficult. But a subfloor system would leave your feet toasty, your hulls warm throughout, and tie directly into your hot water system (possibly on demand heating propane heater). Any thoughts?
     
  2. hump101
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    hump101 Senior Member

    The main problem with underfloor heating in a boat is that most systems rely on having a heavy heat sink to bury the pipes in. However, I don't think this is essential if you use more tightly packed piping and shorter coils. Another advantage of packing the pipe together and shorter coils is that the required inlet water temperature drops significantly, so the efficiency of heating the water increases. This is what we've done in our house, and we can maintain 22C inside with water inlet temperature of only 24-26C, so then you can heat using solar panels, for example, rather than a fuel heat source.

    Even without a heat sink, the piping and water won't be particularly light.
     
  3. saltifinch
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    saltifinch Junior Member

    Hmm I forgot about weight, good point
     
  4. Skyak
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    Skyak Senior Member

    Radiant heating 'feels' warmer and more consistent than forced air. It has mass so a room doesn't blow cold the second a door opens and less volume is taken to distribute the heat. The challenge is insulating below the radiator because it radiates down as much as up -if you don't do it well you are heating a lot of ocean. The other negative is that radiant heat requires a higher temperature (than forced air) so more of your fuel energy goes straight out the flue. Another example is that a heat pump (water to air) can be very effective but it takes too much energy to push the heat to the higher temp needed for radiant.

    Theoretically, water to air heat pump is the most efficient heating on a sail cat.
     
  5. gonzo
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    gonzo Senior Member

    A heat pump is the most efficient system to heat. With the ocean to get energy from, marine systems are small compared to residential. Forced air is not that difficult. Catamarans are thin and long, which makes circulating air evenly much easier.
     
  6. TANSL
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    TANSL Senior Member

    OK, but the thermal inertia of the air is much lower than water so, to conserve heat, you need a continuous supply of hot air. The water however, as in any domestic heating, it is not necessary to heat continuously.
     
  7. saltifinch
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    saltifinch Junior Member

    So stop me if I'm wrong on this, but the length of the subfloor heating on a 30 foot cat would only be about 15 feet at most in each hull, and about 2 feet wide. Assuming you layer insulation under it to minimize heat radiating into the hull bottom, you should have most of your heat directed straight up. I wouldn't run it under the bridgedeck, the heat should naturally rise to that area.

    Heating is a real concern for me, I live in the Pacific Northwest. I'd like to winter in the south, but even spring-fall mornings can get chilly up here.

    I'm not entirely sure how you would properly circulate air in a catamaran, since the two hulls don't tend to share a common airspace. I suppose if you had a central heater on the bridgedeck, and forced air into both hulls, it would probably radiate enough to both ends to heat sufficiently.
     
  8. saltifinch
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    saltifinch Junior Member

    I suppose a more pertinent question is, " am I making this all too complicated."

    I'm trying to build long term reliability, ease of maintenance, and redundancy into my boat. A forced air system tends to fit all those, while a radiant heating system might not. Perhaps an easily removable flooring might make it more accesible and deal with this issue. So glass in a thin layer of foam, install subfloor heating coils, then over top of that a floating floor of some interlocking veneer panels, typical in homes.
     
  9. gonzo
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    gonzo Senior Member

    Catamarans , if the hulls are not connected by a bridge, can have each hull heated individually. It is much cheaper on energy usage.
     
  10. Richard Woods
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    Richard Woods Woods Designs

    Most catamaran cruisers do use forced air. Ideally three outlets, one in each hull, one on the bridgedeck. Of course the major problem is the hot air rising so its hard to heat the hulls and easy to heat the saloon

    I wouldn't try too hard to re-invent the wheel. Many of us, including me, have lived on board catamarans in winter. There is a photo of my first catamaran on my website, covered with 6in of snow, we lived on board for 4 years.

    We got to BC last year April 1st and lived on board our Skoota 28 powercat until May 1st. Two winters earlier we lived on board in Port Ludlow

    The Skoota 36 being built in Vancouver will be a live aboard and the builder is fully lining his whole boat with 50mm insulating foam. It was a lot of work and, surprisingly, extra weight.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  11. Richard Woods
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    Richard Woods Woods Designs

    About 25 years ago I had customers who were living on board a Catalac. They bought an open deck Mira purely because it was easier to heat

    The bridgedeck floor is always cold because of the closeness of the water and the wind blowing underneath

    Richard Woods
     
  12. Skyak
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    Skyak Senior Member

    There are a couple of other considerations. If you have access to fuel and are heating a relatively small volume the smart answer might be to avoid complexity and maintenance. The efficient heat pumps are in response to the cost and weight of hauling fuel.

    What is your electrical system like? If you run a generator regularly for power then you have a ready source of (waste) heat. Co-generation would likely be best and you might be able to do a zone radiant setup. That way you save by only heating where you are.

    The last consideration is cooling. If you need AC the heat pump covers it and the radiant is a complete waste since it doesn't even have the ducts you need for AC.
     
  13. saltifinch
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    saltifinch Junior Member

    I think the best solution, if it exists, is to find an on-demand water heater that burns propane while I'm sailing, and runs on electricity while I'm at shore.
     
  14. Skyak
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    Skyak Senior Member

    OD water heaters certainly exist. I am not sure of the marine premium but home units are quite compact. You can just put them in series. You don't need to find a special dual fuel unit. That still leaves distribution and circulation.

    For control there are loads of geeks that love programming little raspberry-pi boards to control things.
     

  15. Richard Woods
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    Richard Woods Woods Designs

    they are not legal on boats

    RW
     
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