mikeandgerry wrote:http://www.hvaccomputer.com/index.asp is an ASHRAE Manual J online calculator that is available for one month for $49 for homeowners. (Pros can buy it for unlimited use for $389 ) It does both the loss for heating and gain for cooling. I found it to be spot on, easy to use and very detailed. For example, if you have one wall that is half concrete, half of that insulated, half of that uninsulated and the rest of the wall framed and insulated, it allows you the flexibilty to breakdown that wall to calculate those value exactly. It was the best $50 I spent on my project. I would never have followed manual j exactly without it.
Be aware that the manual J analysis software sold by http://www.hvaccomputer.com/index.asp
follows the ACCA, Air Conditioning Contractor Association, manual 7 procedure. It's been superseded by the ACCA manual 8 procedure which claims to give more accurate Btu load number especially for cooling loads, i.e. summertime heat gains. Both will give accurate and very similar results for heating, i.e. wintertime heat loss. I mention this because building code regulations almost always require the latest version of a procedure or specification to be used. So I you are doing an analysis for code approval ask what they will accept before you do anything, especially buy any software.
Mike is correct that a Manual J analysis is very useful and the software makes it easier to do the procedure correctly.