Heat Loss Through Floor?

My fireplace insert is in my family room which, unlike the rest of the house, is over an unheated crawlspace (main part of house has a basement). The family room obviously gets quite warm, but I'm thinking that I may be losing significant heat through the floor due to the cold air below. I'm aware of the modern thinking that says not to insulate crawlspaces (at least the floor). But would this advice still be true in a situation where you are generating your heat right above the unheated crawlspace? Any advice would be appreciated.

I'm kind of thinking of doing the same thing here,,, we have a full basement, 1840's farm house on a 1740's foundation,, stone walls are amazingly stacked straight yet...basement get's down into the 40's over winter, so I'm thinking of stapling up rolls of foil insulation between the massive beams directly to the old sub-floor.. Will it help? I would think so..

i can only add that when i did my addition, similiar layout the foyer is over a 3' crawlspace and before i insulated the crawlspace walls you could feel cold air racing up from the threshold crack. I dry stacked unfaced R38 vertically from vapor pad (3" concrete) up to the subfloor. helped a ton and only used 3 rolls. I did NOT do the joist cavities under the floor. HTH

I like the perimeter of the crawl space insulated. I actually run the forced air furnace fan if it gets too cold, just to circulate some of my heat through the heat runs in the crawl space so there is no chance of freezing pipes. The temperature goes up dramatically in the crawl space when I do that. Also, it is a good way to tone down the heat when I get it too warm in the house, without wasting it opening a window.

The bigger issue is drawing cold air from there if your sill and floor aren't very tight. Heat transfer down is considered minimal enough that you wouldn't see any ROI from insulating it. I did a lot of research on this when considering insulating the basement/living space border. The consensus was as long as your temperature gradient wasn't the same as your exterior walls, it wouldn't be worth it. Now with a crawlspace, seems like it might be ventilated so the temp gradient might be sufficient to warrant insulating....at the very least making sure there aren't any obvious leaks of cold air coming up into your walls and living room.

You just reminded me...I forgot to add that it is ventilated (I've heard conflicting opinions on whether the vents should be closed--it seems to me that even if they were closed, the cold air would eventually work its way under there).

NJ, I keep mine closed year around. The only issue is in the summer, AC season. I have to watch the humidity doesn't get to high.

Same here. Guess there are a lot of factors to consider - but where I am the outside air off the big lake pours in the vents and turns the concrete walls and rat slab into a sweaty mess. I sealed it up tight and run a good crawl space dehumidifier and it stays nice and dry now with the unit hardly cycling at all. Venting vs not venting is one of the most debated topics I ran into when building this place. Since its not a conditioned crawl (no hvac) the code says vent. But that made my crawl much worse so I sealed it and put in the dehumidifier and all is well for 3 years so far.