I bought a 30$ Radioshack IR thermometer just for that purpose, it is
really of limited use, a waste of time. To find out your homes
efficiency get a blower door test done, it tells how many air exchanges
you have and will show you air leaks, apx 2-300. Hire our an IR photo,
you should be able to get someone with a camera to do it for 2-500, it
will be money well spent.