Air sealing for Ultra-Fin

JakeNY

I just saw my brother’s new house and he had Ultra-Fin installed. He was told it doesn’t matter which way he installs fiberglass batts with kraft facing, and no air sealing was done.
I was planning on helping him insulate the rim joist with XPS, and was wondering whether there is any reason why the holes drilled to route the pex should not be sealed with foam. Caulk or spray foam along the joists where they meet the subfloor? Rigid foam under the UF and then Roxul? Am I on the right track using these conventional air sealing methods?

hot_rod

the rum or any cold walk needs to be insulated for both heat loss and air gaps. foam blocks as you describe installed with those cans of expanding foam

Just batts should be fine below fin

Mark Eatherton

Don't forget to isolate zones in the joist bays. That transition between the kitchen and the dining room, if you don't use XPS to delineate the zone, you will get trans zone migration of heat. Maybe not a big deal, but you have an opportunity to do it right, right now. No sense in putting heat where its not needed. It will cause discomfort due to over temp, eventually. Think like energy, flowing from hot to cold...

ME

JakeNY

On an 8” joist, if 5-6” is dedicated to the UF system, how do you support the remaining thickness of the batt that doesn’t fit in the joist? Roxul better than the pink stuff, right?

Alan (California Radiant) Forbes

Our last Ultra-Fin job had 8" joists. You just need 4" (2" above the UF and 2" below) and then used 4" Roxul (R-15) in the bays and 6" Roxul (R-23) at the joist ends.
The Roxul is a tight fit and won't go anywhere unless you've got rats in the crawlspace.

JakeNY

Thanks, I’m in southern NY.
I have been doing a lot of air sealing in my own home this winter and have been using Roxul instead of the pink stuff and it’s great stuff to work with in comparison to fiberglass.

HomerJSmith

I would like to know the thermal efficiency of Ultra-Fin to standard Rehau transfer plates stapled to the bottom of the sub-floor, insulated for back loss. Air is just not a great conductor of heat energy, especially convection. Conduction, I would think works better. Besides, you don't insulate tight against the transfer plates but keep the insulation 2" below the tubing, the best of two worlds--conduction and convection.

Mark Eatherton

Conductivity is the king of heat transfer,,, Air is actually a terrible conductor of heat, hence why we use hydronics. UF requires water temperatures in the area of 180 degrees F in order to deliver the goods. It has its applications, but not in the world of high efficiency heating. I think a person could do the same thing with copper finned tube element...

ME

hot_rod

I have done a few UF jobs running 150SWT, it all depends on the load you are covering, BTU/ sq. ft .

Wasn't all that long ago suspend "bare tube" pex systems were showing 16 BTU/ sq. ft with R1 covering and 140SWT, by some of the pex manufacturer Design Manuals

I think it is good product for adding floor warming to a fin tube system on a conventional boiler, for example.

Their website has all the details you need and independent testing by the Canadian Warnock- Hersey labs.

I'd like to see a time when all hydronic systems operated below 120 SWT, we have the technology.

Alan (California Radiant) Forbes

My experience out here in balmy California, Ultra-Fin runs at surprisingly low water temperatures: 110-120° on 30° days in an uninsulated house. I would call that high efficiency heating, no?

I consistently over-estimate the heating curve when the system goes into operation and the home owners get roasted.