Thank you for replying.I can't help with your question, but many years ago I installed it into a few rooms and found it so expensive to run that we ended up never using it - totally due to the sub-floor.
Has the room got a concrete floor, and if so, is it insulated ? If not, then any heat will just disappear into the concrete. We ended up getting a couple of tiny wall-mounted heaters that did the job for our bathroom and utility room. Even if it is insulated, it will take a fairly long time to warm up enough to feel any difference.
Given the size you quote I'm guessing the room is a toilet or shower room ?
How about a water-filled towel rail with heating element - like this sort of thing, which can be fitted into most towel rails - https://www.toolstation.com/towel-radiator-heating-element/p75892
Much easier to install, quicker to heat a room and easier to replace should there ever be a problem.
I used to use this kit in the top of the line camping pods I used to build, it's good stuff...
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I built 6.6m x 3.3m pods and the underfloor heating was the only source of heat in the entire pod other than a heated towel rail, and these were going up to the top of Scotland, and we never had any issues. I couldn't tell you the cost of running it all the time however.
Having had several properties with porches, I'd say don't bother as you won't need it (unless you intend to spend time sitting in it.
Thank you for the additional info. One more question. Are the ones you linked to okay to plug into a standard electric socket or do they have to be connected back to the rcd with it own connection.
Or am I okay to spur out from an electric socket in the hallway to connect the heating.
The work will be completed by an electrician but just checking my options between this or a proper rad
Best option.Thank you all for the help and suggestions. Had the plumber round and he will just extend the current heading and add a rad in the porch. We will add a thermostat on it so can turn it off if not required.