Hi Are there any good, free calculators out there? I've been using the one on Builditsolar.com but it has some weaknesses.... Thanks mucho. -michael

What weaknesses? What exactly are you looking for in a free heat loss analysis calculator? Are you perhaps wanting to do building energy modeling and not simply a heat loss analysis?

We have a DIY heat loss calculator on our website:

http://www.borstengineeringconstruction.com/Heat_Loss_Analysis_Calculator.html

Please be sure to carefully read the instructions before using this calculator. You will also find other calculators on our website for performing other cooling/heating energy related analysis.

Hi..

Thanks for the calculator. It seems similar to the Builditsolar.com calc. By "weaknesses" I was referring to gettin good loss numbers for slab insulation. I realize this is almost impossible to do well without knowing soil moisture and type etc. But I'm still in the dark as to how much insulation to spec for under slab. Some passive house people use 10-12". Local foundation guys use little if any. I was thinking of using R-15 on perimeter of frost walls and under slab.......

Also, what inside temp should I use? 72? What's typical? (this is Wisconsin, if it matters)

I'm hoping to use these calcs to convince the heating inspector that I can get by with a mini-split, possibly backed up with some baseboard electric. The HVAC guys all want to supersize me.

Thanks!
michael

You could just hire someone to perform a simple manual J calculation which would most certainly pass muster with your inspector. Our heat calculator has the functionality to determine the slab heat loss if you enter the exposed slab perimeter and slab insulation R-value that will be used. Our hydronic radiant design calculator has the functionality to advise the MINIMUM slab R-value that could be used.

If you want to calculate the transfer of heat through the walls and floor you might look into this program.
http://windows.lbl.gov/software/therm/therm.html
You have to modify the factors to use it for wall or floor heat transfer as it is for windows at the moment but if you visit the library some have done that already. It is not easy to use but it is free.

I took a webinar last week where this was explained by an expert working in the field. Synopsis was that I thought the amount of insulation was less than expected for good results.
Hope this helps