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Rich 06-11-2013 09:08 PM

Electric Radiant Floor mat
Looking to install the electric floor mats to keep the tiles warm in the bathrooms. I have the subfloor open as we just replaced all the plumbing. What kind of insulation should be installed in the bays under the bathrooms? Checked at local home improvement store and it appears that the R-38 that they sell would fill the 12" cavities below the floor. Not sure should be using faced or unfaced and if faced should it go up or down? Any thoughts suggestions. These are 2nd floor bathrooms so conditioned space is on the floor below. The ceiling below is plaster and wood lath if it influences the decision. The subfloor is 1" T&G and I'll be adding 1/4" HardiBacker before the heat mat, thinset and tile.

oh'mike 06-11-2013 09:31 PM

No vapor barrier is needed---both sides --ceiling below --and floor above are conditioned.

Do some research here or ask a few questions---you must not install the Hardibacker

directly on top of the old tongue and grove subfloor--that has to much seasonal movement----add a layer of 1/2" BC plywood first--then the Hardibacker.

pgc555 06-11-2013 09:49 PM

Like Mike said. If this is 1" TnG Pine? Yes add PLYWOOD first, then your Hardi.
I like to use SLU to encapsulate and protect the floor heat. MAke sure you use something to "dam" off the perimeter and door openings. I use Edge Strip Kits.

Rich 06-12-2013 07:17 AM

What is SLU? Adding 1/2"ply before the hardi is going to make my finished floor height more than an inch higher than the adjacent rooms. Sounds like what I really should do is remove the remaining T&G instead of trying to get the old back in and start with a new sub completely? If so would 7/16 osb work or do I need to go with the 11/16? Should I use ply instead of osb? Thanks for the heads up on the shifting of the t&g wasn't even thinking of that being an issue.

oh'mike 06-12-2013 07:58 AM

Stick with BC plywood---I suggest you replace the old t&g with 3/4"---

Depending on the floor heat ---the heating coils can be attached directly to the ply---then encapsulated in self leveling compound.

The edge strips mentioned above are like peal and stick
'dams' that do two important things.
They help you determine and keep the liquid level and all the same depth.

They also keep the leveling compound from running under the walls and making a big mess.

Click on the link above----good product---I expect to be using that on an upcoming project---it will sure make the job easier.

Rich 06-12-2013 08:21 AM

Didn't see the link but found the website with a quick search. Product looks awesome and not having to use Hardi would save me 1/4" on my final height. All and all doing it this way I think I'll only be the thinset and tile thickness above the adjacent room. Any specific recommendation for or against any of the floor mats? For the most part the prices seem similar as do the products in general.

oh'mike 06-12-2013 08:46 AM

I've used several types--and brands---
Give me a minute or two and I might be able to find the phone number of my supplier.

For small rooms I have used Nu-Heat---
For a larger job like the upcoming one I will use the loose coils so I can fit the odd shaped layout more easily.

Let me see if I can find the phone number.

pgc555 06-12-2013 09:09 AM

I have installed almost ALL of them. They all will warm the tiles as expected. Only slight differences in them. Some have tape to help hold down, cable systems usually cost a little less and have the flexibility to conform to irregular shapes. All have programmable thermostats for efficiency. All have great warranties. Really it's up to you.LATICRETE may be the only one with a FULL warranty if you use LATICRETE installation products as well ( i.e. thin set , Self-leveler , grouts )

Rich 06-12-2013 04:12 PM

What about the reflective radiant insulation? would it make sense to add that as well on top of the batt insulation or even across the joists before putting down the new sub?

pgc555 06-12-2013 05:39 PM

I guess it wouldn't hurt? If the space below is heated already then you really won't have an extreme temp difference. Any extra insulation below the floor will allow most of the heat to rise - where you want it anyway.

Rich 06-12-2013 08:52 PM

Would 5/8 CD work instead of 3/4 BC? joists range from about 12-22" on center across the space that I'm doing

oh'mike 06-12-2013 11:09 PM

If the span never exceeded 16" you could use 5/8 bc---but with the span going up to 22"--Stick with 3/4" BC---spend the extra--CDX has to many voids to be trusted for tile---the little extra expense is worth it.

frenchelectrican 06-13-2013 01:02 AM


Originally Posted by Rich (Post 1200147)
Would 5/8 CD work instead of 3/4 BC? joists range from about 12-22" on center across the space that I'm doing

Stick with 3/4 inch BC plywood due the spanning spacing.

Make sure the oringal floor joist is good shape before you do anything more with it and double check to make sure you do not have bowed or arched joints if so that will be a good time to deal with it before you do any tile work.


Rich 06-14-2013 10:27 AM

Going to stick with the 3/4". Been held up on this while the floors from adjacent space is being refinished. When I get back in there what would you guys recommend for cuttting the tongue & groove up as close as possible to wall, tub, etc? The multitool/oscillating saw would go closest I think but take pretty long. I looked at the dremel sawmax and similar from rotozip but they only cut up to 3/4" depth. Any thoughts or suggestions?

pgc555 06-14-2013 02:53 PM

Rent a sawzall

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