Low output electric UFH?

[pudding]

Morning,

 

For our new extension which will be approx 40m², I'm planning on using an air2air heat pump and a couple of wall mounted units to provide the heating/cooling in the 2 rooms (study/bedroom, and a dining room). I've used Jeremy's heat loss spreadsheet which gives a heat loss of 565W for the worst case conditions for just the extensions rooms, so 2 small 2kW units such as these will be ample - https://www.saturnsales.co.uk/Daikin-3MXM52N-Outdoor-Unit-3-Emura-Indoor-Units.html (I plan on feeding the extra 3rd unit into our main house for some cooling)

 

Now, onto the UFH bit. We've got wet UFH in the rest of our house. Unfortunately due to the location of the heat pump and manifolds on the opposite side of the house to the new extension, I don't think getting the wet loops out to the new bit is possible (without major disruption), hence going with the above for heating. However, we're planning on having ceramic tiles in the extension and don't want cold floors, which will be especially noticeable if going from nice warm floors in the main house out to the new extension. Soooooo......my current plan is to put some electric UFH in the extension, solely to take the chill off the floor and just warm it to 15-20degs (whatever feels 'good'). In this case, I think we'd probably need the lowest output UFH you can get. Hopefully this current plan sounds reasonable? Any other suggestions welcome. Floor build up is 150mm compacted hardcore/200mm PIR/150mm reinforced slab/15-20mm tiles.

 

The lowest output UFH ive seen so far is this - https://www.theunderfloorheatingstore.com/electric-underfloor-heating/underfloor-heating-loose-cables/100w-prowarm-loose-cable-kit . If i go for this loose cable rather than mats, I suppose I could space the cable out myself to reduce the overall output, but with the danger of cold spots if the spacing is too great. If anyone has any other recommendations for electric UFH that would be great. Also, do these electric UFH systems modulate their output at all, or is it simply full on until the target thermostat temp is reached and then off?

 

Edited January 30, 2020 by pudding

[SteamyTea]

You could use pipes, a pump and a small electric boiler or Willis heater.

Or even s small ASHP.

40 m² is about the habitual floor area of my house. I did wonder about getting the smallest and cheapest ASHP I could find and playing around with it.

[Ferdinand]

Mats can be arranged, and you do not necessarily need to cover the full 40 sqm.

 

You could focus it in on movement areas.

 

F

[Ed Davies]

3 hours ago, pudding said:

…and just warm it to 15-20degs (whatever feels 'good').

 

If you're heating the extension to normal room temperatures around 20 °C and have any reasonable amount of insulation underneath then the tiles will be within a degree or so of that temperature anyway. They'll still feel cool to bare feet or through socks because of the conductivity of most ceramic tiles. To make ceramic tiles not feel cool like that they have to be noticeably warmer in which case they'll be heating the air and the rest of the room so your air-to-air heat pumps will be a bit redundant (apart, maybe, from quick initial heating if you let the temperature fluctuate a lot). Wouldn't it be better to use less conductive flooring?

[pudding]

Thanks for the replies. We'd actually only be heating the dining room (study/bedroom will have carpet so no worries about the floor feeling cold there), which leaves about 28m² for UFH as an option. I found an even cheaper place here for the kit - https://www.ambient-elec.co.uk/ambient-100w-loose-cable-3653-p.asp which i think makes going for a more complicated heating system of pipes/pumps etc too much, both complicated and costwise.
 

Ed - that was my slight concern that if we run the UFH so we can actually tell its on, then the A2A pump and unit will never run and we'll end up using the more expensive electric UFH to proved the heating. It'll still be useful for cooling though. Does anyone know, do the electric UFH systems just run at full chat until the target temp is reached, no way to modulate?

 

One solution is as you say, is to change flooring type. We were tempted to go with engineered oak as elsewhere in the house, from here - https://www.jfjwoodflooring.co.uk/supreme-engineered-oak-flooring-range-21mm-thick-220mm - I've still got a box of it in the garage which will help keep costs down. My concern with using it is the room will have large bifolds in it, and will be a walkway for kids/dogs and adults from outside to inside, so I worried about wear and tear on it. Maybe an entrance mat/runner and it'll be fine. Certainly the cheaper simpler option and removes the need for the UFH. Hmmm......

Edited January 30, 2020 by pudding