DIY baseboard hot water heat design help for a single room

Discussion in 'HVAC Heating & Cooling' started by dabiz7, Jan 31, 2014.

  1. dabiz7

    dabiz7 New Member

    Feb 27, 2008
    Location: sw Ohio
    Sunroom, 22' x 16'
    Windows: Seven (7) Polaris Thermaweld double hung, double pane, low-e glass, 36" x 52"
    Doors; One (1) steel full lite, 36 x 80, one (1) double patio steel full lite (72 x 80
    Floor: Slab, engineered wood floating floor
    Walls: 3 sides, normal 2 x 4 frame construction, r13?

    We have a sunroom added to our house, right now it is a 3 season room because the builders didn't really include a means to heat it in the winter.
    Just using some rough heat load calculators fromt he internet, I need around 3500 btu/hr.

    Floor radiant heat is not an option. I am thinking of designing a mini-baseboard hot water sytem for this room. A mini-boiler, an accumulator, 4 gpm pump, several runs of baseboard heaters, a wall thermostat to cut the pump on and off.
    I have looked at some of the manuf. sites like SlantFin, I think these should put off plenty of heat.
    I'm not sure about a mini-boiler? Electrical requirement? I would like to run the boiler and pump off an existing 120v, 15 amp circuit. Is that possible.

    If anyone knows a manufacturer that makes a DIY solution for a one-room area, that would be helpful.

  2. Dana

    Dana In the trades

    Jan 14, 2009
    Your issue with the boiler is one of putting out too MUCH heat, and short-cycling on baseboard heaters more than having too little. If the fuel is propane or oil you'll be better off heating/cooling the room with a mini-split heat pump, but if on natural gas there are water-heater solutions to think about.

    I'm seriously doubting the 3500 BTU/hr number unless you're in an unusually warm spot in SW OH, but it's under 10K for sure. Just your windows and door lossed add up to more than 3500 BTU/hr!

    The quick & dirty heat load calc runs something like this:

    Figuring a 99% outside design temp of +10F, and an indoor temp of +70F that's a 60F delta-T.

    Without looking it up, assume the windows have U-factor of about 0.35 BTU/degree-foot-hour, or 60F x 0.35= 21 BTU/hr per square foot. (Unless they're something special and expensive, that'll be close enough.) Each window is 13 square feet, so with 7 windows your window losses are 7 x 13' x 21 BTU/hr= 1911 BTU/hr.

    If they're clear-glass (no low-E, no argon fill) the sliders and doors have a U-factor of about 0.5, and a heat loss of 60F x 0.5= 30BTU/hr per square foot. Combined you have 60 square feet of door, for a heat loss of 60' x 30 BTU/ft-hr= 1800 BTU/hr

    Assuming you have at least R19 in the ceiling the ceiling U-factor will be less than 0.06 BTU/degree-hour-ft, and with 22x16 = 352 square feet of ceiling that's an upper-bound loss of 0.06 x 60F x 352= 1267 BTU/hr.

    With 2x4/R13 construction the U-factor of the walls is about 0.1 BTU per hour per degree-F per square foot. So at a 60F delta that's about 0.1 x 60F= 6 BTU per square foot of exterior wall area. (Make up a spreadsheet, and do the measuring.) If the common-wall to the rest of the house 16' long and you have 9' ceilings, the exterior walls are about 9' x (22' +22+ 16')= 540' of gross wall area, less 91' of window and 60' of door for about 390' of wall area. At 6 BTU/ft- hr that's 2340 BTU/ft-hr

    Add it all up and you're at about 3.7K for windows and doors, 3.6K for walls and ceiling for 7.3 KBTU/hr heat load at +10F outdoor temps. With a GENEROUS 30% margin for air leakage and thermal bridging through the slab make that 1.3 x 7.3K= 9.5KBTU/hr max. And there's no way it'll be under 6 KBTU/hr, even with a super-insulated ceiling plus slab-edge insulation.

    A pretty-good 3/4 ton mini-split like the Fujitsu AOU-9RLS2 or Mitsubishi MSZ-FE09NA could more than cover that load, and even the smallest boilers would be 5x oversized for that load, and that's probably the best solution here, since you'd also get high-efficiency air conditioning out of the deal. The hardware itself isn't all that expensive, about $1500 at internet pricing. Add another fifty or hundred for bracket mounting or a pouring a concrete pad. As a mostly-DIY maybe $150-200 in reefer-tech time to do the refrigerant charge and initial testing (with all the right tools that you don't want to own, and the experience you probably don't have), you're talking 2 grand. A complete turnkey all-pro installation might run between $2.5-3K. Operating costs will be comparable to heating with an 80% natural gas boiler, maybe a bit less, depending on what your actual gas/electricity rates are.
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  4. dabiz7

    dabiz7 New Member

    Feb 27, 2008
    Thank you for the info on heat loss calc.
    I would like to run this past everyone again, as I really think this is my best option, as opposed to radiant floor, electric baseboard, or a 'mini-split'

    I want to use an Electro EMB-S-2 mini-boiler

    small pump, 2-4 gph plus the thermostat that comes with the boiler.

    2- 8' Slant Fin FineLine/30 baseboard along one wall under five (5) windows and 1- 8' baseboard under adjacent wall under two (2) windows

    I am thinking 2-3 gallons of water should be sufficient.

    Even if this is overkill for this size room, I doubt the wife will complain.

    Thoughts? useful advice? Forget the whole thing?
  5. Dana

    Dana In the trades

    Jan 14, 2009
    So you're looking at three 8' baseboards + intermediate plumbing, plus a pump and zone-relay- that's going to run you something on the order of $500-600, plus the $700 for the electric boiler, call it $1200-1300 in hardware.

    A better-class 3/4 ton mini-split is about $1500 at internet prices, well under $2K if it's a mostly DIY installation. It puts out more heat, modulates with load for super-stable room temps, and uses 1/3 the amount of electricity of the electric boiler + baseboard solution.

    You don't have to freeze-protect it the way you would a hydronic solution in a lossy window-room, and it air conditions at high efficiency.
    Last edited: Feb 12, 2014
  6. dabiz7

    dabiz7 New Member

    Feb 27, 2008
    I am really trying to see yur point about the mini-split. The AC advantage is really not applicable, the wife just opens all the windows and she prefers this.
    I am thinking that the price differential would be greater, I think the baseboards, plumbing and pump can be done a lot cheaper here.
    I would have to pay someone to do the initial refrigerant charge on the mini-split, right? How much would that be?

    I'm thinking that I can do the baseboard option for close to $1000.

    What I was hoping was, could someone comment about this option's effectiveness at heating in the cold winter, bassd on my proposed components?
    Could this mini-boiler meet the demand? I think it only goes to 160 F.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Every watt you put into a resistance heater is just that, one watt...every watt you use to run a heat pump can produce as many as 2-4 watts to heat things, depending on the efficiency and the outside temp. So, it's not only the hardware costs, it's the overall cost to run the thing.
  8. dabiz7

    dabiz7 New Member

    Feb 27, 2008
    I downloaded Don Sleeth's HVAC-Calc Residential 4.0 and ran it for just my one room.
    It was saying I need 17K + BTU to heat this room per its baseboard heat calculator.
    That seems like a lot to me. Comments ????
  9. Dana

    Dana In the trades

    Jan 14, 2009
    A heat load of 17K seems almost high for a 350' room (about 50BTU per square foot, which would consistent with heat load of an uninsulated horribly leaky house, or a pretty-tight tent) especially given that one of the four walls is a common-wall to a conditioned space. What were you using for indoor & outdoor design temps? Is there any single-pane glass? I could believe 10KBTU/hr with a huge allowance for air-infiltration, but 17K is over the top.

    Even if you can install an electric boiler & baseboards for a grand, and 3/4-1-ton mini-split costs two grand ($1500-1700 internet sourced hardware + $200-300 in electrician + refrigeration-tech time) the mini-split will still pay for itself and fast. The napkin math goes like this:

    Assuming you have a 10KBTU/hr load at a 60F delta-T (10F outdoors/70F indoors), if it were 10F for 24 hours that would be a 60 heating degree days, and 240,000 BTU, for 240,000/60= 4000 BTU/HDD. To deliver that 4000 BTU with an electric boiler takes 4000/3412= 1.17 kwh.

    Dayton sees about 5600 heating degree days/year, Cincinnati about 5200, so you'll be using something on the order of 1.17 x 5200= ~6000kwh/year to heat the place.

    At Ohio's average residential retail rate of 12 cents/kwh, it'll cost about

    $0.12 x 6000kwh= $720/year to heat that room.

    But in your climate a better-class mini-split will use less than 1/3 that amount, costing at most $240/year, a savings of at LEAST $480/year. Making up the $1K difference in cost takes less than three heating seasons, and might be done in two, depending on what how actual heating seasons turn out from a heating degre-days perspective.

    If my 401K had that kind of internal rate of return I'd have retired decades ago!
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