There is a reason people doing only one room usually use the electric mats. I think you'll need to speak with a licensed installer in your area for some firm price numbers. What little I know comes from watching the system in my own home take shape.

Since this type system is usually done for the whole house, most of the equipment is sized and priced for larger applications. Odds are high that using it only in a bath will be even more expensive than the electric mats, which aren't cheap by any means.

Your first consideration will be where to put the heating pipes. The closer the tubes are to the surface, the more efficient the transfer of heat from the water to your room. The cheapest approach is to staple them up under the floor joists and insulate below them so you don't end up insulating the entire space beneath.

For systems that go above the subfloor, gypcrete [a low weight concrete] was pretty standard for a while, but it has its drawbacks, and there are a lot of alternative products appearing. Essentially, chanels routed into ply wood to accept the tubing, often backed with aluminum sheets to reflect and spread the heat. Warmboard is a product intended to replace your subfloor entirely, and has a very thick aluminum layer. Pricey, can't say if its worth it.

The other products go on top your subfloor, so they can add unwanted height. Not a big issue if you plan in advance.

Then you'll need a heat exchanger or separate boiler for the heat system: Water heaters are typically set for around 120f degrees, your floor heat should be closer to 85. An exchanger runs the hoter water through the heating fluid to acheive the correct temp.

Then you'll need a pumping system to move the water through the floor when the thermostat calls for it.

You should see the mechanical room for my whole house system: so many pipes, pumps, valves and dials that it looks like something from 20,000 Leagues Under the Sea.

I totally agree with oruboris... unless you're doing true radiant for the whole house I can't see that the investment in the equipment would be worth it for one room. We have whole house, under slab radiant, and have a whole room dedicated to the equipment necessary to run it... pipes, manifold, boiler, valves, etc...

Why are you adverse to using the mats?

i just put the electric mats in my bath under tile.8by 14ft. materials cost $550 with programable thermostat. works beautiful.

www.heatizon.com is an electric system that is neat, but a bit pricey for whole house. Might be ok for a single room.

I looked at both the pex option and heat mats for our master bath suite.

the issue I ran into was access from below. most of the bathroom floor was accesable below from the basement but not all of it. there were beams, hvac ducts, wires - a lot of things in the way. I still could have done it but it would have been a royal pain.

the heat mats and tstat cost about $1000 for roughly 200 square feet. we also had to pay the tile contractor another 3 dollars a square foot to install the mats into a mud base. so the entire thing cost 1700 dollars. we could only afford to do a portion of our master suite.

i remember that the hydro approach was going to run about $2500 or so and included all pumps, tubes, insulation, plumbing parts and a small hot water tank.

if i had complete unovtsructed access from below, i would have done a hydro system myself. it would have allowed me to defer some cost and it really does not look to be that hard. i could have also warmed more of the master bath suite - we have 2 closets and a dressing area - and the hydro system can be expanded for the small cost of extra tubing and insulation - assuming the pump and tank you buy can accomodate the length of the loop.

all the parts for a hydro system can be purchased online. if you have total access to the floor from below you might want to conider this approach.

i hope this info helps.

to oruboris
Just how large of a room does it take for all the equipment in a full house system. I am thinking about warmboard in a 2 story home and also putting in a ground source heat pump.

My mech room is really complex due to extras like central vac, breaker box, generator breaker box, heat exchange from a hot spring, etc.

For my 5500 ft home, I think the actual boiler and valves could have been fit into a 10x10, possibly even an 8x8 if the door had been in the right spot and the plumbers had planned carefully. There are a couple of manifold sets that distribute the water to individual heating loops stashed in closets elswhere in the house as well.

A small hydronic system, such as only for the bathroom, can be run off the regular hot water system. Involves tubes and thermostats but not manifolds.

I've been studying about SIP (and similar well insulated) houses which actually do whole-house radiant flooring using 2 standard hot water heaters. Real-life experiences are showing that a simple method can be just as effective and considerably less expensive than the better-known -or better advertised- systems. Keep in mind that insulation and overall square footage are important when choosing which system. Also keep in mind that using solar-assist in water heating (whether for direct use or for room heating) can drastically reduce the future cost of heating.

I have radiant floor heating (pex) on my first floor. Oh, it is wonderful. Our second floor has only a finished bonus room. Sadly I have cold floors up there.
I would think the pex would be a more expensive way to go for just one bathroom. If you will have the same results with the electric for less to install why would you want to spend the extra? Does the heat from the electric mats feel different?
I have two walls of gadgets that run my radiant. I was worried when I saw it being installed. Thankfully, it runs itself.

hydronic vs electric: In my case, the build is wa-a-ay out in the country and losing electricity during storms is an expectation. Neighbor tells me to expect loss during most major snowstorms. If you have heat mats, no electricity means no heat. Also, you are tied to the utility company for cost of operation -- rates are not likely to go down, in my area, electricity $ has almost doubled in the past 5 years. In my case, solar-assist hot water is expected to make the future cost of operation nearly nil; and the planned extra storage tanks are expected to maintain sufficient heat for 3 to 7 days (locally, this is longer than most blizzards).

I have a hydronic system (PEX in gypcrete, mostly raised foundation but some slab) in my 7,100 square foot home (actually, more square footage than that, since we did the garage, too). I can't speak to the issues associated with doing just one room but here are some things that I've learned along the way, some the hard way.

1. You can heat the house with a standard hot water heater (ours was a 100 gallon commercial model that also provided domestic hot water for half the house). But expect it to last only half as long (~ five years) because of the load that the radiant system puts on it. We replaced ours at great expense ($12K) with an 80 gallon Phoenix boiler/hot water heater: 96% efficient (vs. ~70% for a water heater), compact and should have a 20 year lifespan.
2. Use caution selecting the pad under any carpeting. Surprisingly, the carpet isn't a big issue for radiant floors but the pad can significantly impair the heat transfer. Best option: slab foam rubber (expensive and hard to find). Next best: corrugated foam rubber. Absolute worst: rebond.
3. Don't set the temperature back at night if you have a high thermal mass (e.g., gypcrete) system. It's actually less energy-efficient to bring the floor back up to temperature each morning than to maintain it throughout the night. It's OK to turn the thermostat down while on vacation.
4. Use the forum for the Radiant Panel Association (http://radnet.groupee.net/groupee/forums) to get opinions from installers on all sorts of radiant floor issues.
5. Finally, here are some pros/cons that not everyone considers with radiant systems. a) It takes a LONG time for the system to heat a cold house (10-12 hours or more). Having a forced air furnace as back-up is important if you turn the system down while on vacation. Likewise, if it's too warm in the house, it will take a long time to cool down after lowering the thermostat. b) Radiant systems heat your extremities better than other heating systems because the warmest part of the room is at floor level. This makes you FEEL warmer in a cooler room. c) Radiant systems keep the heat from rising to the ceiling in rooms with high ceilings because the heat is evenly distributed and can't readily be displaced by cold air in order to rise. d) If you have stone floors as we do, you'll love walking on them barefoot in the winter.

We love our warm floors and won't trade them for forced air until we head for the rest home. Hope this helps.

Bob