Electric U/F heating and tiles

[GMM]

I'm slowly (given the amount of adhesive to mix!) tiling the floor of our hall and continuing into the downstairs bog. At present, the bog ( a single storey part of the ground floor) has no heating and gets a bit cold / damp, so I'm thinking of slapping some electric U/F heating (probably the Screwfix mat) under the tiles (can't raise the floor enough to accommodate wet U/F). It's only a small area so, once I upgrade the insulation, I'm hoping it will at least keep the chill off in winter.

Two questions:

First, has anyone had good or bad experience with the Screwfix heating mats? They seem competitive on price and I'm assuming that a run of resistance cable is a run of resistance cable...but you never know (!)

Second, the options seem to be to press the mat into flexible tile adhesive or to stick it to the floor and cover in self-levelling compound. I'm inclined toward the former (never yet managed to get a level finish from self-levelling compound!), but perhaps someone out there knows the pros and cons of these approaches....

Thanks people...

[The Natural Philosopher]

From a heat transfer POV the nearer the surface it is the better it will be efficiency wise..that being a function of the conductivity to where you want it to the conductivity to the cold hard ground ;-)

If you are happy to level up with cement, why not simply lay a leter of cement and teh mat on top, and thenlay another layer and tile onto that.

[Colin Wilson]

What type of floor is it - wood or concrete ? Ours is concrete, and we didn't use any insulation, which we may(?) regret later, but we didn't want to raise the floor if we could help it :-}

I got a little paranoid about ours, as I didn't want to have any under fittings, but if anything, I underestimated the size of mat i'd need. My dad did the bathroom, and he dropped a minor (luckily correctable) bollock by locating the sensor too far away initially - it's now closer, but probably not optimally located.

Our stat is set to 23degC but most is around 26C with one specific spot getting closer to 29C, and the mat was laid direct in tile adhesive.

We almost bought our mat from screwfix, but ended up getting it at tlc-direct due to needing some kit screwfix didn't sell.

As far as I can tell, they're pretty much identical, we got these:

programmable switch looks complicated at first, but it's surprisingly easy to set up, and comes with a good preset programme that might only need slight tweaking (we needed to add heating for an extra couple of days as my wife is part time)

The first thing i'd do is measure up the floor area properly - mine's in now so it's too late, but hopefully you can avoid my mistake and not get cold spots in front of the basin and where your feet go when you're on the bog :-}

[GMM]

Thanks chaps. I'm in pretty much the same situation as you were Colin: A concrete floor and a fairly low ceiling, with the level running right through from the adjacent hallway in the same tiles, so I'll have to forego insulation in favour of not banging me head on the lights...

The TLC mats look to be pretty much the same as the Screwfix ones, but they seem bit cheaper (possibly worth the inconvenience of taking a week off to guess when the delivery might turn up).

I think the point about planning is well made - also, since the room is empty of fittings right now, a good plan of where things might go into the floor (eg screws holding the bog down) might be an idea (!)

I'm not entirely convinced that these things will ever do any more than stop the room/pipes etc from freezing, but that would be a start.

It seems the simple way is to lay it in adhesive, although the data sheet from Screwfix says it should be the flexible sort, which will be fun when all the tiles slump!

[The Natural Philosopher]

Or dig down deeper. However even without insulation, you wil get reasonable efficiency. You will end up with a warm hemisphere of soil under the floor..and a HUGE time constant since you will be as much heating a few tonnes of soil as the room.

This makes it even MORE important to get it as close to the room surface as possible.

Yes. its not a good idea, it's bloody essential., Although I don't screw bogs down these days. Thanks to Uk.d-i-y I use a load of silicone to glue them. Seems to work better than screws!

If you pump in about 100W/sq meter, and the room is reaosonably well insulated, it wll do a lot more than that.

Well lay the mat in flexible, and use rapid set for the tiles that go on top.

[GMM]

I can't really dig it out - The solid floor is already there so it would make a much bigger job to do much about the levels. I have a feeling that I'll have a lot of happy worms a foot under the bog in winter(!)

Indeed, it might be an opportunity to try the silicone approach, although I think I'll allow for the possibility of screws, just in case it goes pear-shaped...

If it keeps the room above freezing, it will be a move forward, though I have a feeling I'll need to attend to the walls and ceiling (single storey, flat roof, 3 outside walls) to make it cosy in any sense!

I had thought of that, although I was wondering whether they specify flexible so that it 'gives' rather than cracks as the element heats and cools.

[terry]

On Jun 26, 7:42=A0am, The Natural Philosopher wrote: =2E

Interesting number. Seeing that our house is all-electric.

Just comparing ....... our 10 foot square (approximately 9 sq. metres) fairly windy corner of house bedroom in reasonably well insulated (1970s wood frame construction in a slightly colder than UK climate) has a 1500 watt electric baseboard heater. That's about 167 watts per sq. metre.

Small (no more than 6 sq. metres) bathroom in centre of house (no outside walls or windows) has 500 watt baseboard which during much of the year doesn't cut in at all when the six 40 watt bulbs above the vanity are on! So that's about 500/6 =3D 84 watts per sq. metre. At (6 x 40)/6 =3D 40 watts per sq. metre.

One argument is that the warmth being near the feet and then rising, in floor heating is more 'effective' (don't go near the discussion of 'more efficient'!) from comfort viewpoint?

Also that in-floor is 'slower to respond' (which may be true if one measures the ambient room temp.?).

Any thoughts on these comparisons?

[The Natural Philosopher]

Oh definitely. Subjectively you can run at air temps about 2C cooler than when you have a cold floor and rads.

Something like a 4 day time constant here..