Re: Will adding insulation under floor make my room warmer in summer?
Sealing and insulating any ducts that are in unconditioned space will provide greater cost savings than insulation under the floor. If your ducts are uninsulated metal and the seams aren't sealed (painted with a gray substance called duct mastic or covered with foil tape), do that first -- it will provide the greatest return on investment. The duct mastic is messy, but easy for a do-it-yourselfer. You smear it on with rubber gloves.
That said, insulation will probably help keep your house cooler in the summer, even if the space below is cool. You see, that space isn't as cool as the air traveling through your ducts.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.