Heat loss

cm6230

stumbled upon US boilers free heat loss calculator online. Has anyone used this to get you close ?

Seems pretty good, what are your opinions?

hot_rod

better than guessing. The more data you can enter into a program the more accurate the results.

But a number of assumptions need to be made regardless, unless you do a blower door to nail down infiltration, maybe an infrared scan to check insulation quality.

pecmsg

Historical Fuel Usage

HVAC Load Calculation - Maunualj - Whole House Loadcalc

Kaos

For existing structure, the quickest and most accurate heat load is from fuel use. Older houses have too many unknows for any Man J type of calculation to be accurate. In case of fuel use about the only error is boiler efficiency, DHW loads and passive solar gains.

The math is pretty straight forward:

https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

If you want even quicker, in zone 5,6, winter fuel use in Therms X 42 is about your heat loss. So if you burn 1000Therms of gas, your heat loss is around 42000BTU.

hot_rod

If the home uses gas or LP for cooking, DHW the numbers will be skewed. Solar gain, wood stove, indoor gains also.

The online load calcs are quick and easy for a double check.

usboiler.net has one

hydronicpros.com has a free trial version

If you are old school and have a tape measure.

https://www.scribd.com/document/553217971/Heat-Loss-Table2011