Heat Load Calculations: Need help to determine Heat Load for home in NE Massachusetts

Discussion in 'Boiler Forum' started by danboston, Mar 22, 2011.

  1. danboston

    danboston New Member

    Mar 19, 2011
    Lawrence, Massachusetts
    I am trying to determine the Heat Load for my home. We (two adults and one child) live in a 50-year old ranch in northeastern MA. The total square footage of the ground floor is 1,700 ft2 and the basement is 1,500 ft2. The house is currently heated with a circa 1950's tankless American Standard oil boiler (Arcoliner 3B J3 series) and a forced hot water Mono Flo baseboard aluminum fin system on two zones. The total length of the baseboard emitters is 145 feet and they are all on the ground floor. There are no heating elements in the basement. The boiler provides all the heat and hot water for the house. We currently run out of hot water quickly if two showers are taken back-to-back or if the forced hot water heating system kicks on when in the shower. The ground floor of the house is well insulated with all new windows. I am currently insulating the basement using dri-core panels on the floor, R-13 foamboard on the walls and R-30 batts in the ceiling.

    In 2010, we burned 720 gallons of oil. The total number of heating degree days in 2010 for our area totalled 5,778. If I did this correct, this yields a K-factor of 8 (5,778/720). I tried the NORA Fuel Savings Analysis (FSA) calculator and it gave me a design day heat load of about 30,000 btu/hr when I input Boston, MA as the location and a K-factor of 8. When I input the following boiler parameters, it came very close to the amount of oil that I burned in 2010 (i.e., 720 gals):

    Location: MA - Boston (gives Design Temp = -2 F)
    K-Factor: 8
    Boiler: 88 AFUE WELL INSULATED DIRECT BOILER (I have an old tankless coil boiler)
    Steady State efficiency: 87.5
    Idle Loss: 0.7%
    Heating Capacity: 10,500
    Hot Water Load: 65 gal/day

    This yeilded the following output:
    Annual Efficiency: 81.6%
    Annual Oil Consumption: 714 gal
    Summer Oil Consumption: 0.5 gal

    HOWEVER, when I input the Boiler as: OLD BOILER WITH TANKLESS COIL (which is what I have), I got output that was 300 gals of "oil consumed" higher than what we saw in 2010:
    Annual Efficiency: 55.3%
    Annual Oil Consumption: 1,054 gal
    Summer Oil Consumption: 1.1 gal

    Does the Design Day Heat Load of 30,000 btu/hr seem appropriate given the size of the house, weather conditions, and other parameters (amount of insulation, length of baseboard heaters, etc.)?

    Secondly, the oil boiler folks who come for annual maintenance and measure the efficiency tell me it is about 83% efficient. I was considering changing the boiler out for a either a new high efficiency Burnham oil boiler or to gas. Until I figure out the appropriate heat load for the house, I do not want to make a move since the current boiler has no operating issues.

    Are there any other free calculators out there where I can do other comparisons?

    Please help. Thanks, Dan
  2. tk03

    tk03 New Member

    Jan 31, 2011
    Harrisburg, pa
    You really do not mention the insulation values of the first floor. A 1700 (basement usually has very little heat loss) sq ft home if insulated decent could very well be about 30k. The contractor is measuring combustion efficiency. Combustion efficiency today is normally around 85% to 87%, not a whole lot of change. The thermal efficiency is the big change. How much heat is actually being transferred into the water heating your home. Another big change is GET AWAY FROM BOILERS WITH DOMESTIC HOT WATER COILS IN THEM!!!! Sorry for yelling but maintaining water temperature today is a huge waste of money. Use a three pass boiler (cold start) with an indirect water heater.
    Since you mentioned Burnham the MPO-IQ system is unique with the IQ control set-up on it. You can run the IWH right off the boiler and not require a separate relay which is easy to prioritize the IWH. Plug in ODR control and LWCO if needed is also a plug in control.
    If going gas the ES2 or Series 3 if you chimney vent. In about 3 months, if on schedule, the IQ will be on a sidewall vented gas boiler boiler which will be power vented or sealed combustion.
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  4. danboston

    danboston New Member

    Mar 19, 2011
    Lawrence, Massachusetts
    I had a contractor come by yesterday. He was a veteran who has been in business for over 40 years doing only boilers. He told me that since we have a Mono-Flo baseboard heating system with aluminum fins (not cast iron), then he does not recommend a gas-fired high-efficiency mod-con boiler. The main reason being that the return water ends up being too hot and therefore the boiler will never have a chance to enter into condensing mode. If we had cast-iron fins, or a radiant heating system, then he said that is a much better situation for a mod-con boiler since the return water ends up being much cooler. Because the gas company wants to charge me $6,200 to move the gas main 100 feet to the front of my house, he recommended I stick with oil. He recomended a Burnham MPO-IQ115 high-efficiency (87%) 3-pass oil-fired boiler. This is a cast iron water boiler with a heating capacity of 98,000 btu/hr and a weather sensitive control that adjusts the boiler temperature up or down based on outdoor air temperature.

    For an indirect water heater, he recommended the Burnham Alliance AL50SL. This is a 50-gallon, seamless hydrastone-lined tank that has a first hour rating of 225 gal/hr and continuous draw rating of 171 gal/hr with a 6 gpm flow rate. He said that would work fine to fill a 70-gal jacuzzi and still be able to supply hot water for other uses.

    Again, the house (ranch) is well insulated. We had treated cellulose blown into the wall cavities as well as, 15" in the attic. We also have replaced all the windows, including the basement. We have 150 total feet of Mono-Flo baseboard heating with aluminum fins. The square footage of the ground floor is 1,700 ft2 and the basement area is 1,500 ft2. I plan to insulate and heat the basement as well (the basement will have dri-core panels on the floor, R-13 foamboard on the walls, and R-30 fiberglass batts in the ceiling).

    He initially wanted to install the next higher-sized boiler (129,000 btu/hr), but when told about the insulation, he said that the lower boiler with a 98,000 btu/hr would be fine. Does that sound like the right size?
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