The layout on the spreadsheet is great.
I the best way to do it all would be a web form. With Excel on a remote PC is possible. But I have problems with that. Microsoft Excel works well with M$Sql, its possible to do an odbc connection to mysql… last time I was playing with stuff like that you needed a MySQL odbc driver installed. Secondly not everyone will have excel. You may have version compatibility problems(Have you used Excel 2007 yet, I haven’t). Then your need to save the sql authentication in the spreadsheet someone where someone wouldn’t crack it. On an intranet it might be feasible, but on the internet. Conversion might be possible, but I think a web form from scratch would be best.
Personally I have done perl and asp scripting, but that’s not my strong point as I’m a network guy. With the right background it isn’t hard to read some how-to’s and sample scripts to put together a working script. You already have the php/mysql server, so you have a good backend. You can use your server for dev, or your local box. You can easily install php and mysql on your local PC for dev, along with apache or windows. The hard part for me is to make the input and output looks slick.
Using a simple input like hearth.com has on http://www.hearth.com/econtent/index.ph ... alculator/
with the nice output on the spreadsheet would be my goal. When everything is calculated, you would have an option to dump that to a database(the database part would be last, after your have your calculations and output down). Then you could build reports.
Once you have one built, it would be easy to do another one for say… How much do your burn per sq ft, with options for central heat vs parlor burner, boilers vs warm air, brand burner, stoker vs hand fired, hot water coil vs none, year stove made, etc.
I’d offer you what I could as far as help however my free time is far and few between with a young family.
Check your email for screenshots of the spreadsheet output.