Both DW and BIL (who is a residential contractor) insist that we stuff FG insulation under and around new fiberglass bathtub. Say it will warm up quicker and be more comfortable taking a bath. Tub is on exterior wall that is about R30, over a conditioned crawl space.
I’m concerned that FG installation in a sealed off space like that which is subject to large temperature swings will promote moisture and mold. My solution to more comfortable baths/showers would be yo run hotter water.
When I installed radiant floor heat I decided to NOT place tubes and plates under the tub. Maybe that was a mistake but too late now.
Question is, do any of you routinely insulate the hollow space beneath/around bathtubs? Remodelers…when you remodel bathrooms, do you see more evidence of mold where insulaiton was placed as above than where it was not?
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That's a bit curious all around on me--I usually have to have an argument with the plumber about installing (per the tub instructions) a mortar support bet under FG tub units.
But, then again, with the durock, etc., up, the surround wall have mass that kind of obviates insulating the actual tub.
Unless they meant a product like low-expanding foam--which would help support the tub unit. It would also give some insulating value as well.
Mind you, I'm also basing this from experience in Texas, I just started in on my 80-85 heating degree days on Friday. Probably will not have a full heating degree day this week, too.
"Cool to touch" tub rather nice when it's 80º plus outside . . . (that would be just last Saturday).
Yep, I spent about 5 years in the San Antonio area. On a dairy farm, we used to run plastic H2O supply lines one spade-ful deep!
This, however, is SE MN. With 1/2" PEX running 120* fluid 8" O/C right underneath the cement board and tile in the main floor area of this bathroom, I think it will be plenty warm already. Also, this tub is designed to self-support with no mortar bed.
My off-the-cuff response would be skip it.
Fiberglass tubs don't conduct heat/cold like steel or cast iron. So the little heat loss/gain into the area would be insignificant. Seems like that area is going to be pretty close to inside ambient inside temp provided a tight wall on exterior.
What about tapping into the radiant system and taking a couple of loops in the under tub area to insure some heat in there if you want a pre-warmed tub? Even a little radiator. Is the tub gonna get used a lot?