Bathroom Remodel - Some Basic Insulation Questions for Radiant Floor

smore1945 · March 7

I'm remodeling a 2nd floor bathroom and I'm interested in adding hydronic radiant floor heating. I've identified a couple different products/methods for this installation but I can't decide which is better for my situation.

The two products I'm considering are uponor quik trak panels, and uponor fast trak panels. I haven't done an in depth cost comparison yet, so at the moment I'm interested in whether one is better than the other for my situation.

My main concern is how I'll properly insulate under the panels. If I use the quik trak plywood panels is it ok to use rigid foam insulation between the sub floor and the panel? If I use the fast trak panel can I do the same? The fast trak 1.3i panel would be ideal with the incorporated insulation but it looks like those have been discontinued.

The existing subfloor is warped and rotted in places so it will be replaced. I could add insulation between the joists. Is that sufficient? I'm thinking any insulation is better than no insulation, but I'm worried the 'correct' r-value in rigid foam might be too thick.

I could ramble on forever but I'll leave it here. I'd love to hear some recommendations for my situation or experiences with either of these products.

Ironman · March 7

How many square feet is the bathroom? How old is the house? What’s heating it now? Have you done a Manual J load calculation to determine the actual heat loss?

hot_rod · March 7

Floor warming, or trying to actually heat the space? A room with no other heat source?

Is it over a cold crawl space? Why is there no insulation in the joist bays now? The heat load of the room will depend on what is below, a heated or cold space.

The panels with foam work well for over the top. Roth for example, although other brands are available now.

The Roth panel lets you use 6" OC spacing, 3/8" tube for easy installation.

smore1945 · March 8

Thanks for the responses, I'll try and answer some of your questions.

The bathroom is 50sqft, 28sqft of heated floor. The bathroom is on the 2nd floor of a two story 60 year old house and the space beneath is heated living space. The bathroom is currently heated like the rest of the house with forced air but due to some renovations below I need to remove the duct that supplies the bathroom. I haven't done a full manual J but chatgpt helped me come up with about 900 BTU/hr, but that number presumed adequate insulation in the floor.

The roth panels you mentioned look like they'd do the trick. Unfortunately I can't find anywhere online to buy them, so I'm guessing they're one of those B2B contractor only companies where I'd have to jump through all kinds of hoops with a sales person, so I'm going to stick with the uponor products that are easily available and seem to be competitively priced.

psb75 · March 8

There is also Warmboard R. This is their renovation board. I believe this has insulation under it. Warmboard S is thicker with subfloor under it. I think the spacing is 12" for 1/2" tubing. Also Sunboard Radiant and Ecowarm.

hot_rod · March 8

I get them from LowEnergy in Denver

Also available in NY

Are you going to run this as a separate zone

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IMG_9884.jpeg

? What type of boiler do you have?

It will be a tiny zone and could cause an issue for the boiler run time

Mad Dog_2 · March 8

Forced Air heat? The most economical way to do this is use a small water heater to supply the radiant tubing. Mad Dog

smore1945 · March 8

Thanks again for all the suggestions and comments. I have tons of little questions about this project but I'll save those for separate posts so the discussion are topical and useful for future readers.

Regardless of the brand, I'm considering 2 different methods/product types. One is a plywood panel with grooves for holding the tube. The second is what I've learned is generally called a "castellated" panel that has nubs that hold the tube and requires concrete or similar to be poured on top. Would any of you experts recommend one method over the other for my situation? And if so how would you insulate?

Kaos · March 8

Generally for a remodel project you want to match the tile height to flooring height in the hallway. This means you don't really want anything above the subfloor.

If you don't have a boiler, your best bet is one of the resistance heated mats that go directly under tile. Something like Ditra heat works great, simple install and takes up minimal height.

If you do have a boiler, I would run the heat pipes through the joists. Since you are pulling up the subfloor to replace it, you can run the pipes there and install heat spreaders like UltraFin. When doing this type of heated cavity, make sure to air seal the rim joist area with rigid foam sealed in place with canned foam. Outside air leaks are the enemy of this type of install. You can also insulated bellow the pipes with regular batts.

If you don't have a boiler, you can still do the above install if you use the hot water recirc loop. This only works for small areas which sounds like what you have. The idea is to loop the recirc line under the floor before returning it to the water heater. This should only add a couple of extra feet of pipe. In the winter you can run the recirc all the time to heat the place and on a timer in the summer. The key to this is the water must always be periodically circulated to avoid stagnation.

hot_rod · March 8

If you can get under the room, that opens more options.

Any on top system will raise the floor level. Perhaps there is a layer that could be removed if it were an old mud set? There are transition strips to accomodate a small difference in floor levels from room to room.

I would go with electric cable or mat,

or a small 2-1/2 or 6 gallon electric tank if you want pipes instead of wires :)

An example of my go to tank system for master bath floors and walls.

hot_rod · March 8

smore1945 · March 8

I'm set on using hydronics and not electric, I already have the heating source for the water worked out, and I'm set on installing above the joists; I don't have access from below. I've got the details of matching the floor level mostly worked out, but the amount and type and thickness of the insulation is the variable I'm trying to solve for, so that's why I'm asking about the choice between the two different methods.

I can do the math to figure out the R-value needed, but I'm trying to figure out how exactly to go about installing the insulation. I'm guessing I can use rigid foam between the sub floor and the quik trak (plywood type) panel without issue, what about the same with the fast trak (concrete pour type) panels? Do I need a vapor barrier or moisture barrier underneath if I'm pouring the underlayment? What about a decoupling membrane under the thinset and tile?

ILikeEmOlder · March 8

From the perspective of a home remodeler:

I think installing insulation above the subfloor in your situation is a non-starter. Trying to accomodate for the extra height of the finished floor is a nightmare scenario is most cases. You are talking about at least an additional 3/4” of height (relative to the connecting hallway and rooms adjacent to the bathroom).

I’ve spent my career as a carpenter (working almost exclusively on older houses), and I can tell you that old houses often present these exact challenges, and the solutions are always a PITA, and always cost a lot of money to execute.

I strongly suggest that you rethink this one.

Kaos · 1:46AM

I've installed ultra fins from the top without issues, no need for ceiling access. Pull up the subfloor, drill the joists, put down the batt insulation and air seal rim area, run the pipes, clip on the fins, put subfloor back down. Pretty quick install and since the pipes are well bellow the subfloor you don't have to worry about stray nails.

With old house, make sure the check all your joists and level as needed. For a good tile install especially larger format, the joists should be perfectly flat.

If you really must go for above subfloor, you don't need to insulate. There will be some heat going to the space bellow but since that is part of the conditioned space, the heat isn't lost. The only time this might be an issue is if you have a bedroom bellow the bath in which case you might overheat that bedroom.

Bathroom Remodel - Some Basic Insulation Questions for Radiant Floor

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