underfloor heating advice

[a-z electrics]

Morning all,
I may have to quote for electric underfloor heating for a new kitchen, flooring insulation boards are going in now so will be well insulated.. I never done any before, what is better - mats or cable and any recommendations? Ive looked at heatmat.co.uk you can get thin 3mm or 7mm cables, the latter has to be set in screed first, the former can go in the tile adhesive (I wont be doing the tiling).
the floor is about 25 - 30m2 and my initial research would suggest we're looking at about 5kw peak load.

obviously a dedicated circuit but what to use and what protection to put in (new) dist bd? contactors have been mentioned but dont know anything about these, never had to use them before..
Thanks in advance.

 

[Octopus]

Strikes me as the installer/designer you have too many unanswered questions so you could be in trouble with this one.

I'd start by asking the client if they have ANY idea of how much it will cost to run, because I wouldn't want one that size in my house!

 

[a-z electrics]

I should have said - it'll be on economy 7 tariff..

 

[Octopus]

I should have said - it'll be on economy 7 tariff..

so it won't work for 17 hours per day??

 

[Rockingit]

Let's put it like this: I'm a sparky, and (I like to think, anyway) a good one with lots of experience, who knows my way around the products and the methods, blah blah blah.

I'm installing WET underfloor heating in my new extension at home as the area is too large to be economic to run any other way!! The only wiring therefore is a room stat and new zone off the combi!

 

[a-z electrics]

so it won't work for 17 hours per day??

Well i guess it could be configured to be boosted during the day if necessary but the logic is it heats up overnight and releases the heat during the day, like a storage heater - the coldest time of use is going to be first thing in the morning, just when its been fully charged.. the solid floor acts as a heat sink...... but I was really asking for advice if anyone had any experience of them.

 

[a-z electrics]

I'm installing WET underfloor heating in my new extension at home as the area is too large to be economic to run any other way!! The only wiring therefore is a room stat and new zone off the combi![/QUOTE]
This is heated by gas I presume? theres no gas at this property..

 

[Rockingit]

This is heated by gas I presume? theres no gas at this property..

In which case, that's a fair comment!! What you have to remember is that whilst, yes, underfloor htg does take a little while to get to temperature, and also to cool down, it's not like a storage heater! It'll be pretty cold by late morning and stay that way. If it's running on peak rate at lets say 14p/kwh, that's roughly £160 a month alone (based on 8hrs running). And customers have this knack of very quickly forgetting that you told them so when they start to get the bills in - prepare for the call-backs!!

 

[stuartcourt]

I take it at that KW its the primary heat source and not just to take chill from tiles

 

[AndyL]

Well i guess it could be configured to be boosted during the day if necessary but the logic is it heats up overnight and releases the heat during the day, like a storage heater - the coldest time of use is going to be first thing in the morning, just when its been fully charged.. the solid floor acts as a heat sink...... but I was really asking for advice if anyone had any experience of them.

Have fitted a few, but never on E7, pretty sure heat will be dissipated much too quickly for this to be effective.
Heatmat is very easy to fit, all nicely spaced out etc for quick installation times

p.s is the floor measurement the entire room or the usable floor space, dont want to be heating under cupboards and appliances

 

[a-z electrics]

I take it at that KW its the primary heat source and not just to take chill from tiles

Correct - it is a big kitchen 6x6m but usable floorspace is more like 5x5 max.

 

[Octopus]

Well.... if you do send a quote to the client I would include on it a "warning" about the ongoing running costs so at the very least they can't say you didn't tell them.

I worked with a chap 18 months ago and he had 5 underfloor heating systems installed in his house. I've been back on a number of occassions since and they NEVER have had any of the floors on!