Under Floor Heating in a first floor bathroom

tails_naf

Hi All,
I am in the process of building a new house and have decided to put under-floor heating in the upstairs bathrooms (nice warm tile effect under foot really appeals to me).

It seems this is not that easy though - I have been looking into a few options:

1) In-between joists - using either aluminumum heat-spreader plates, or insulation and a thin sand-cement screed is one thing that is done. However, I wonder if the heat will really penetrate througn the 18mm osb above, as well as the 10mm plywood above that, and then the tile?

(As far as I can see online, you must have at least 18mm osb and then a furhter sheet of plywood to allow the floor to expand in a way that will not cause the tile to lift).

The problem with this method is: the floor is already nailed down (timber frame, floor was installed before I knew it), so will have to run pipes from the bottom side - not easy!



2) Batten out 1" battens on top of the existing 18mm osb, 200mm centers top add the 10mm plywood and then tiles. Use sand-cement between battens and run the ufh pipe in this.
This has advantages in that its easier (work done from the top), cheaper - no need for heat spreaders, and distance between the heat source is smaller as the heat must only travel through the 10mm ply.
The downsides are: a) is this good enough for tile, 10mm osb on 200mm centers battens, and b) this will create a floor level that is at least 1" above the other floors - causing a step up into each room.

So, can the wise people of boards direct me to the best solution. The 1" step into the bathroom sounds like something that would always bother me - but also the heat penetration through 18mm osb and then 10mm ply is also a concern. It feels like a real rock and hard place type decision!

browner85

Another option is an eletric heat mat that you put between your ply an tiles has the same effect!!

tails_naf

Hi Browner85,

Thanks for this - I had actually looked into this, but it's fairly expensive. I'm talking about 20m2 total bathroom area (1 main bath and 2 en-suites), and quick costings seem to suggest I'd be shelling out 2 grand for this.

I already have the materials (inclduing manifold, pump control, stats, etc) for the wet-underfloor heating, which is why I'm really trying to avoid the mats if at all possible!

Joey the lips

In between the joist works out the cheapest. It might be cheaper for you ro consider going through from the floor underneath.;) Plasterboard and plasterer will already be on site.

antoinolachtnai

The heat will penetrate through all the OSB and so on if you do it that way. You don't lose any actual heat.

The problem is how long it will take. It could take a day or two for the whole thing to heat up or cool down.

For any of the piped systems you'll need a heat exchanger, no? Otherwise the water in those pipes will be too hot. That is going to cost a bit. You will also need extra electric valves and all the rest of it for your heating system. The materials for raising the floor will cost a bit too and you will have a tough time getting a finish you are really happy with.

Where are you going to get the hot water to run it? You will need to run your heating in the middle of the night so as to insure that the floor is warm in the morning.

if you have a step up to the bathrooms, I think you will have a problem when you go to sell your house in the future.

You should be able to do the matting for less than the price you mention. Have a look at http://www.floorheating.com/products.php?CAT_ID=3 for instance. Note - I don't know anything about that company, and there are plenty others selling this stuff in the UK and in Ireland if you search on google. Also, you don't have to cover every single square foot of the bathrooms. Just the main 'walks' is enough. It will cost extra to tile at the increased height due to the matting, mind.

tails_naf

Hi antoinolachtnai,
Thanks for that link - the prices there seem to be much better than others I've seen - it certinaly makes the electric option a runner again.

As I already have the manifold/mixer/pipe/stats/control etc I may still opt to put in that first and see what the response time for heating is (try it on a small en0suite first). The good news is I have a buffer tank onto my oil boiler which should have a good store of hot water which can be pumped throughout the house as needed.

Thanks again for the advice and link

antoinolachtnai

ah, do you already have underfloor somewhere else? - that makes a bit of sense.

Going back to the piped options - why not take up the floor and put it down again? Builder won't enjoy that but work is work. I wouldn't rather do that than have to put in heating from below with my hands above my head.