My experience of our underfloor is completely in contrast to everything I heard/read about them. I read that they take hours to come up to temp, to the point where you have to ideally leave them on "all the time" or basically a lot. We moved into a house where the kitchen diner has it throughout and we just gambled that it worked basically. We did not know what to expect.
Ours is a wet system which I know little about other than it is plumbed into our main heating system but controllable separately (ish). It has it's own thermostat/programmer, but it's rubbish because it seems to only have on or off, rather than one where you can set a temp and then it turns off when reached. I think it's just a basic "come on between X and Y on these days" type thing. I should replace it. We use it by manually just turning it on, and then turn it off when we are satisfied with the room temp later on. In one of the kitchen cupboards there is a manifold where it all feeds/terminates.
It just works. Really, really well. From switching on from very cold first thing on a winter morning (typically the room might be about 15c at this point) , you can feel a noticeable temp difference after 15-20 minutes. I haven't done any official measurements of time to warm up, but it is no different than a room with radiators. Probably better in fact. Within an hour the room will have gone up 2 or 3 degrees and within 1.5 to 2 hours it will reach 21c. The tiles are obviously nice and warm on your feet, but you will get cold spots based on where the wet loop does and doesn't cover. This is fine though. The floor being warm under feet is just an additional nice to have. The room gets evenly warm and I love not having radiators taking up space.
We find it plenty responsive and have never had an issue with it.
In contrast....we have an electric system in our downstairs toilet. I again don't know anything of the spec, but it's probably a very small loop/pad under the floor tiles. This literally does take hours to get up to temp and make a difference. It definitely works, it's just more designed with its controller to have these "comfort" and "economy" periods. So you set it for example that between 7-9am you want it in comfort mode, then to go to economy whilst everyone is out. Then you set it to come back into comfort mode for say 3pm until 9pm. In economy mode it sort of ticks over around 22c floor temp. During comfort I have it set to about 30c floor temp. it never really reaches that though as it's a very cold room. Definitely takes the edge of though and works, but I dread to think the elec cost of it. I have no easy way to measure the usage of it until I get an in home thing for my smart meter to see how much it uses. We generally tend to only have it on during very cold spells and just do without it otherwise. I mean how comfortable do you need your number 2 to be?
I don't know how good elec ones have got now, but I would favour a wet system from my experience.
