Heating formulas

I am installing a new hot water boiler replacing the existing one. Have added more space. Where do i find a calculation sheet to determine boiler size?

You're talking about a heating boiler, right?

What you need to do won't fit on one spreadsheet. You need to do a Manual J load calculation to find the heating needs of your space and then size the boiler as required. Manual J is very involved; the only practical way to do the calculation is with specialized software. HVAC Calc and RHVAC work well.

Even Manual J is just an estimate.

Have you heated your home and additional space through a winter with the existing boiler? If so and if you have a monthly record of utility usage, then you could combine that with daily average temps over the same periods to estimate actual sizing required. The usage over a given time period with given average temperature can be scaled to determine peak usage at the design temps.

http://www.hvaccomputer.com/hvac/tofc2.asp

homeowner version is 50$.



This is free, but I'm not sure how thorough/accurate it is.

http://www.bgmsupply.com/calculateheatloss.asp



Also very basic / simplified, but will give you a rough idea, at least:

http://www.pprbd.org/plancheck/Heat Loss Table.pdf

www.taco-hvac.com has a free version that is very good