Goofed on Underfloor Heating Wattage

[john56897452]

So fitted Quartz starstone floor tiles. Used Mapei super flexible UFH compatible adhesive on screwed and glued 6mm Hardie backer board. Finished with Granfix maxigrout flexible grout.

Floor area about 1.3msq so smallish. I checked with the supplier (Tile choice ) and tiles ok for 150 watt UFH. Turns out I have fitted 300w warmup loose wire. Not switched on at all yet or commissioned. Has quartz tile technology come on enough yet or is my floor doomed?

I may add I have no intention of using full heat just maybe 20 degrees or so to take the chill off the tiles in cold weather. Main heating in this small en suite is a radiator. Any expert advice on my options beside the obvious of don't switch on.

 

[Uheat - Jake]

Knowing nothing about the tile side, what spacings have you got the cable at? As that's 230w/m2 which is more than likey below the minimum fixing distance for a heating cable to be fixed at which could be very dangerous.

 

[mma]

Are those tiles suitable for ufh?? Heat sources can cause the tiles to warp. Done some Quartz recently and it said on the box, not suitable for conservatories...

 

[john56897452]

Fixing wire 50 to 70mm. As stated above supplier said good for 150w UFH.

Many thanks

 

[Qwerty]

As far as I see it you only have one sensible option..... give it a go and see what happens!

 

[Qwerty]

Just had a brainwave...... I'm no electrician, but is there any way that a sparky could reduce the wattage down that is fed to the cable to 150w????

 

[Dumbo]

I thought more wattage just got you to temperature quicker not making floor any hotter so don't know what the problem is if that is the case .

 

[Qwerty]

Not sure. @john56897452 why don't you ask on our sister electrician forum? www.electriciansforums.co.uk

 

[Old Mod]

Warm up have a 24hr hotline, and it is pretty good to be fair.
I must admit, I thought the distance for warm up cable was 70-110mm... 90mm being the optimum.

With the Ditra Heat E I've just installed,
3 nib separation gives 136w (which they recommend for floors) and 2 nib separation gives approx 200w, which is what they recommend for walls.
Must admit I've never heard of a 300w installation.

 

[john56897452]

Think I've solved it. I can use a 300w+ dimmer switch between the wire and the thermostat. This will give total control to adjust the wattage.....hence the heat, and still be controlled by the floor sensor for temperature. This will give the best possible conditions for warming the tiles limiting shock heat. I can place a meter in series with the heat wire and adjust the wattage current reading to take into account initial warm up and continuous use. Could set it for 100w to give the tiles the best chance, with slow controlled warm up.

 

[Qwerty]

Out of interest was this a solution from the electricians forum?

 

[john56897452]

No......I clicked from your answer re lowering the wattage. Many thanks for that.

Might help other people with the quartz tile UHF confliction. Dimmers for 700w plus are available.

 

[Uheat - Jake]

No......I clicked from your answer re lowering the wattage. Many thanks for that.

Might help other people with the quartz tile UHF confliction. Dimmers for 700w plus are available.

A dimmer switch wouldn't be suitable for use with UFH.
A dimmer takes away voltage therefore dropping the voltage of the heating cable below 230v will not give any power to the cable thus not heating the element at all and most likey buring the dimmer out.

 

[john56897452]

Surely dropping the voltage drops the current available drawn by the heating cable hence controlling the heat (current drawn = heat, the max at 240v would be 300w). How can say a 700w rated dimmer be burnt out by a 300w max load? The cable is rated for 240v not dependent on 240v. Applying voltage via a variac would produce the same results.

Using ohms law 240v at 300w would draw 1.25a. The current would not change by varying the voltage but the wattage would. If the voltage dropped to 120v the wattage rated by the heater wires would be 150w. Conversely to drop the wattage to a low 100w would require a voltage reduction to 80v. I think.

 

[Flintstone]

I don't beleive there is a 300w kit available.
On the subject of spacing, the warm up dcm pro, which is probably the same cable, have a strange recommendation, can anyone enlighten me on how you run that at 190w per m? Do you alternate the spacing ?