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Boiler for small camp w/radiant

sadie72sadie72 Posts: 1Member
I have a well insulated 24x26 1.5 story camp on 5" slab with 2x300' 1/2" pex radiant installed above 4" XPS insulation. 3/4 bath with LP gas in northern Vermont. Any opinions on installing a Rinnai E50c boiler with 13600 - 50000 btu/hr? Short cycle? Any general problems with small condensing boilers?

Comments

  • Mark EathertonMark Eatherton Posts: 5,843Member
    Quite honestly, this is a very open ended question. You need to fill in a BUNCH of data before a good answer can be given. It all starts with a room by room heat loss calculation. Once that is done, we can give you some good advice.

    I did seek out the manufacturers literature, and from what I can see, they've come a long ways baby.

    I did some quick back of the napkin math, assumed a value per square foot (20 btuH), and yes, it looks like short cycling will be a potential issue. Short cycling is guaranteed trouble for ANY peice of equipment. The hardest thing you can do to any piece of equipment, is to START it up.

    This particular appliance looks like it was designed and intended for space heating applications, which is a good thing. Taking an appliance that was designed to heat DHW from 40 to 120 is a completely different animal than one that will be seeing a shorter (10 to 20 degree F) differential. If you decide to go this route, make DARNED sure you follow the manufacturers instruction to the T. Otherwise, you may not have any warranty.

    Personally, I've never installed any Rinnai products, so will have to defer to others who frequent this site for their experience with the actual brand name.

    Have you looked at any of the other brands, or was price your first consideration? Some times, least expensive to purchase is most expensive to install and operate and maintain and probably has a short life expectancy.

    How is the half story being heated, and what are you doing for DHW?

    There are FREE online heating load calcualtors. Start there, and once you have a reasonable load factor, get back to us for guidance.

    Also, make certain you neutralize the condensate before discharging into the sanitary sewer. Ithas been found that the low pH has a tendency to cause the septic tanks to fail at the air/water line due to acidic corrosion exposure. You wouldn't think it would be an issue, but I am aware of numerous situations where the condensing boiler has been blamed for tank failure.

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • SWEISWEI Posts: 7,356Member
    edited August 2015
    Is there electricity available?

    What are the rates for electricity and LPG?
  • RobGRobG Posts: 1,850Member
    SWEI said:

    Is there electricity available?

    What are the rates for electricity and LPG?

    I think where SWEI is going with his questions is that if your electric rates are comparable or less than LP you may want to look at using an electric boiler as they come in much smaller sizes and offer the same features. Look at the Thermolic brand boilers to get an idea of what is available. They take up very little space and don't require any venting.
  • HardBoiledHardBoiled Posts: 2Member
    Looks like a good application for the boiler. The Rinnai E50c will run up to 99% partial load efficiency on slab radiant. And it is a reliable, easy to service boiler in my experience. Just keep in mind the DHW is only 85kBTU which does not go a long way in northern VT. You will get a 2gpm shower no problem, but multiple simultaneous hot water fixtures won't be in the cards.

    Mark has a good point about nailing down the heat loss. You may want to upsize if the building heat loss is well above 30kBTU. If not you have the right boiler size wise. I am not aware of another cd combi boiler with a heating output below 60kBTU.

    If you have LP on site you don't want an electric boiler. Even at $3 a gallon LPG is far cheaper that electricity ($0.16+/kWH with the the effiency charges), and if you are not on GMP your juice could be even pricier. Here is a good calculator to work up a comparison of LPG vs El costs per BTU: www.eia.gov/tools/faqs/heatcalc.xls

    Good Luck.
  • SWEISWEI Posts: 7,356Member
    Don't forget the other part of the equation (ROI) which is driven by occupancy. We have $3 per gallon LPG here as well, and the payback for an oversized LPG boiler in a small space is marginal for a regularly-occupied dwelling. For an intermittently-occupied space, the electrons easily win here.
  • hot_rodhot_rod Posts: 12,395Member
    Could be the load is around 10- 15,000BTU/hr for that space? Run a calc.

    If so an electric WH tank with a 4500W element, dedicated to the radiant, while not officially a boiler, could produce 15,345 BTU/hr. Self buffered. Maybe under 300 bucks for a DHW tank. Looks like the Rinnai on Amazon runs $2400.00? Add gas, flue, etc.

    I agree with Kurt, for small space, intermittent use applications electric has a place.

    Load calc, cost of fuels, $$ of investment, service and reliability all come into the decision. It is very inexpensive to keep a sealed system, electric WH running for 20 years or more.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • RobGRobG Posts: 1,850Member

    Looks like a good application for the boiler. The Rinnai E50c will run up to 99% partial load efficiency on slab radiant. And it is a reliable, easy to service boiler in my experience. Just keep in mind the DHW is only 85kBTU which does not go a long way in northern VT. You will get a 2gpm shower no problem, but multiple simultaneous hot water fixtures won't be in the cards.

    Mark has a good point about nailing down the heat loss. You may want to upsize if the building heat loss is well above 30kBTU. If not you have the right boiler size wise. I am not aware of another cd combi boiler with a heating output below 60kBTU.

    If you have LP on site you don't want an electric boiler. Even at $3 a gallon LPG is far cheaper that electricity ($0.16+/kWH with the the effiency charges), and if you are not on GMP your juice could be even pricier. Here is a good calculator to work up a comparison of LPG vs El costs per BTU: www.eia.gov/tools/faqs/heatcalc.xls

    Good Luck.

    I will take a WAG and bet that HardBoiled either works for or is affiliated with Rinnai.
  • Big-DBig-D Posts: 21Member
    Agree with the electrons winning. At $3.00/gallon LP based on say...90% efficient gas boiler will equate to 13.85 cents/kWh. If you can receive electric power less than this kWh rate then your money ahead on the energy aspect, let alone the less expensive front end cost of the electric boiler in comparison to the gas boiler.
  • Tom_133Tom_133 Posts: 657Member
    Currently in Vermont LP is on average 1.50 a gallon cheaper if you shop around or prebuy.

    The rinnai is a great choice make sure someone will service it for you, and that they know their stuff.
    Tom
    Montpelier Vt
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