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