Everyone here does schluter ditra heat for electric radiant heat now. I havent seen suntouch or any of the other products used in a coon's age. Ditra is just fast and easy. I would have zero qualms using it. Insulate the slab, ditraheat your guest room, and you will be golden. 

One day Miss Kitty need to procure a camera.

A build thread with no pictures... for shame!

Great minds or something!

I'm living on finished concrete floors in Texas and don't have a problem with them. Loved on plenty of slab floors before and never had an issue.

I will say bare foot on concrete all day is t the most comfortable thing for your feet. You'll end up with a rug somewhere.

Insulating a concrete slab can be done by using insulation board, such as Foamular 250, under the slab. It's typically 2" think and it must be the foam board rated for the higher pressures of a concrete slab sitting on top of it, such as the Foamular 250 I mentioned.

Do like they sometimes do up north.Have the concrete floor slab heated.I think they do it with hot water,but not sure.Might be electric?

Fur slippers are cheaper than a heated floor.  So are rugs.  

I would have liked to put in the heat mesh when I did my master bath, but I just didn't have time.  

Deadline too tight to drop in a new circuit.  

Yes.

Check out this article and this article from Building Science Corp. They have lots of useful information regarding building techniques.

We had both our bathrooms tiled.

The upstairs bathroom does not have in-floor heating, but the downstairs' does.

Love the in floor heating and wish we had done it in both bathrooms.

We did the single wire in floor heating.  Didn't notice much difference in the heating bill.

Maybe a few more details on this?

Wow, Kitty, your plumbing rough-in is impressive!

Suntouch tapemat requires modified mortar or thinset.

One of the reasons we use the original custom spyder mat vs Ditra was we could  use modified mortar.

We just completed demo of a tiled restaurant.

In the kitchen, they installed the quarry tile with a good quality modified thinset.
That required a jackhammer to remove and half of the thinset is still stuck to the floor.

In the dining areas they used unmodified cheap thinset for the tile.
With a flat wide chiseled rock bar, you could pop out 20 tiles easily with a running start, kind of like playing shuffleboard with no thinset attached to the floor.

Granted this is a 4,000 psi floor that was power troweled & fully cured, but a good example of adhesion of the 2 types of thinset.

If budget is a concern, drop the heated floor and just put down the 1” of xps.  It won't be warm, but it won't be cold.  

A radiant heat lamp or small heater (built in or portable) can give you spot warming if you find you really need it.

We retrofit radiant heat under the first floor of my house.  I used enough pex and Thermofin to have water temps range from 70 to 145 with outdoor temps between 35 and 20 below zero.  Surface temp no greater than 85. Constant circulation with outdoor reset means the floor is never cold (though it also never feels warm until 10 below), the kids and wife run around barefoot in January.  It was expensive but I do not regret it one bit.

Hi Kitties,

Yes I did the work myself.  I replied without reading all of the thread so I was thinking you might still be up in the air about insulating under the slab.
Our house had baseboard electric, and I heard from friends of the previous owners that they had trouble paying the electric bill during the winter.  My estimate was that I was looking at a $500 per month average electric bill for the heating season.  I didn't want to retrofit a forced air system due to difficulty of installing it from the basement through the second story, so that left water.

The basic steps:

Do the math to figure out the expected heat loss.  Uponor and Zurn, two PEX tubing and fitting manufacturers, have good free design manuals that walk you through the calculations based on outdoor temperature, R value in walls, window and door type and sizes, square footage of walls, losses due to wind infiltration, etc.

Follow this with the math to see what heat input you need to stay warm.  I needed 30 btu per square foot to maintain an indoor temperature of 68F when it is -20F outside.  If you have a heated floor, wall, or ceiling you gain about 2 btu per square foot for every degree the surface is above your desired temperature.  The maximum surface temperature for floors should not exceed 85F, which is driven by the water temperature and how well the heat transfers from the tube to and through the floor.  In your case, burying pex in the concrete slab would have given a very good thermal transfer.  In my case stapling pex to the underside of the wood subfloor would have given a poor thermal transfer.  I needed a very good transfer to meet the 30 btu per square foot.

So I bought a bunch of Thermofin C which is a heavy aluminum extrusion. Thermofin C  Other manufacturers make similar products, including Uponor.

To install the extrusions I needed to take an angle grinder and remove the nail and screw points from the underside of the subfloor.
Upgraded eye protection, $10;  Angle grinder, $50;  Kids checking out the noise and asking "Why is dada shooting sparks across the basement?"  Priceless.

3/4" self piercing hex head or truss head screws and a small impact driver had the extrusions up against the underside of the floor quickly.  I put two lines of extrusions, each 20 feet in length, in each of the 22 joist cavities.

Then I drilled holes in the ends of the joists, pulled a quarter mile of pex tubing, and tapped it into the extrusions with a rubber mallet.  The tubing runs are a little over 300 feet each and start and return to a manifold where a very low wattage pump runs all the time to distribute the water from the boiler.

The boiler is a modulating and condensing type, which means that it adjusts the fire rate based on outdoor temperatures, and also operate with low water temperatures to extract almost all of the heat from the flue gasses.

The result of all of this is an even warm feel and floors that aren't cold.  When it is 35 degrees out, the water in the tubes might be 80 degrees.  The floor surface temperature is only about 71 or 72, and it doesn't feel warm, but it won't feel cool on bare feet either.  In a house with forced air the tile floor would likely be 58 or 60 and would definitely feel cool.  As the temperature outdoors drops the boiler automatically increases the temperature of the water.  When it is 10 below the water is up to 135 or so and the floor surface is close to 80, which is warm to the touch.  We have a couple of indoor thermometers that read between 65 and 70 ... generally depending on how much cooking and baking my wife is doing.  An air temperature of 65, with a floor temperature of 80 feels downright cozy on a cold winter night.

Contrast that with the seasonal cottage I will be staying at while deer hunting in a couple of days.  Built on a slab with very little insulation in the walls.  The gas wall furnace will heat the air to 85 degrees and shut off, but the 35 degree slab and 40 degree walls suck the warmth from you.

I also pulled pex tubing from a second manifold to a panel radiator in each bedroom on the second floor.  Thermostatic valves on each radiator allow each bedroom to be set to the desired temperature.  Ours is a little cooler than the kids' rooms.

Anyway, all that to say installing all this was a bunch of money and work, but it has paid itself back in electricity savings and we don't regret it one bit.  My wife has Raynauds syndrome and she appreciates not having to wear slippers inside to keep her feet from going numb.

Installing a radiant system like this is a lot easier in new construction, especially prior to pouring a slab.  It might not be for everyone, downsides compared to forced air include cost and limited options for air conditioning, but it is certainly worth considering.

My son rehabilitated a home on a slab. He put down a bamboo floor that looked like hardwood over a styrofoam liner. It was plenty warm in the winter and did not conduct the cold from the slab. His baby ran around on it barefoot with no problem.

My heat is propane.  The pre buy price for this year is $1.69/gallon, which is about $1.82 per 100k btu.
Our electric price is about $.14/kWh, which is about $4.10 per 100k btu.
I wish I had natural gas at $.79/100k btu.

The boiler was about $2000.  There are systems in this area that use plain gas or electric water heaters as the heat source, with a valve system that either mixes water to the right temperature and uses a constant circulating pump or a valve that opens and closes to obtain the right slab temperature based on outdoor air temperature.

If you wanted to insulate over your slab and use water for heat transfer you could install a product called Joist Trak (there are also similar products or make it yourself), or put gypcrete over the insulation.

Rugs work too.  Or splurge on a good set of slippers and save all that money and effort.