Hey Andy, years back I had a stove in the basement, the hottest I could get it down there was less than 70. I used a Ram-set, put 1" nailers on the concrete walls, 2 ft centers, then 1" styro. boards on them. What a difference, all that cold concrete was covered up. One thing I have to add though - All those styrene insulating products are a fire hazard, according to the building inspector. He wanted 1/2" sheetrock or 1/4" plywood over it. I finally found some fire retardant paint that he approved. 40.00/gal, but that was easier than sheetrock. What kind of wood is giving you 7 hours off 4 pieces? I think thats pretty good. My Harman boiler, I load 14 pieces in at 10:00 pm, if it's really cold, like below 10F, it's pretty much gone at 5:00 am when I get up -