We're having a small extension built in April - new area is adding about 3m x 3m to the kitchen, and then knocking out some internal walls to have a larger kitchen-diner. Standard sort of thing, nothing particularly fancy. As we'll be laying new floors throughout the new bit, there's an opportunity to install UFH, and I'm trying to decide if it's worth it. The area is about 30m^2, and the hardware alone is probably about £1k. We've had a quote for nearly £4k for supply/fit/commission - I expect we could get it cheaper but I've not shopped around yet.
It'll run off a (old) gas combi boiler. If the boiler were to die tomorrow we'd just replace it, but I'm conscious that in ~5+ years, air source heat pumps might be cheaper/better than they are at the moment, or gas even more ridiculously expensive, so having UFH installed would make that transition easier.
At the moment we're quite frugal with the heating - 30 mins in the morning, 30 mins in the evening, and occasionally 30 mins here and there to top up when it's really cold. The house is moderately well insulated. We have a wood burner which gets a fair bit of use and probably saves us a lot on CH bills.
The concerns I have are a) UFH is expensive to install - £2-3k more than radiators, and b) it'll force us to run the heating more to make it work properly. I know with UFH it takes a while to warm up, and holds the heat for longer, but I feel like compared to current usage, we'll probably be burning more gas. The main reason to go for it seems to be future proofing, and it being much easier to do it now than in a few years. We'd want two large rads as an alternative, and the room layout only really allows for one at the moment. And I guess it'd be nice to have that room a more constant temperature, especially for working from home.
Sorry for waffling on. Does anyone have any advice or anecdotes for me please?!
Go for electric in the extension to take the edge off under foot and as background warmth in the room.
Saying that you sound quite hardy with your 30 min x2
So buy some slippers and a Wooly jumper and keep warm chopping and carrying wood👍
We did a similar extension. i broke out half of the existing floor so we could have underfloor heating on all the tiled area. It is brilliant but we had 30 tons of cart away and i have vibration white finger!
For UFH to work, it’s really about heating the floor slab as a ‘sink’ and then it slowly radiates that heat into the room - the floor slab needs to be well-insulated or you end up heating the earth. We have wet UFH in our house (with ASHP) you don’t really notice it’s on. If you just want to take the chill off the floor in the morning, electric might be better/cheaper.
I've got ufh in a 30m^2 kitchen extension and it's great. Would prefer it everywhere downstairs if I could. Just make sure you get the right controls fitted to the boiler so you can get a load modulating boiler next time,especially if using 2 zones.
I would avoid electric UFH, if there was a fault somewhere your floors coming up. Wet systems are much more reliable. Also the flow temp of your UfH would be about 40 degrees whilst your rads work on a flow temp of 72 which isn’t so energy efficient. Insulate the floor as much as possible. Are you going to have to raise you finished floor level and have a step into the kitchen or can you install it all and keep the same level. What type of floor do you have? Suspended or ground bearing?
Suspended floor which is down two steps, so there won't be a lip to step over. Full cellar below so access to insulate well between the joists. It's definitely possible to do a decent job, just hard to decide if it's worth the expense!
You can install wet UFH yourself, it’s not hard. With part of the room being lower, it might also be the best option as conventional rads will send the heat up the wall then along the ceiling to the higher ceiling in the other part of the room. (If I’m understanding your post properly). UFH will feel warmer in a sunken room.
We have a UFH house (built on insulated concrete slab and with concrete block floors upstairs). Your expectations of UFH “ At the moment we’re quite frugal with the heating – 30 mins in the morning, 30 mins in the evening, and occasionally 30 mins here and there to top up when it’s really cold.” just doesn’t fit with how it’s best used. Leave it on and maintain a constant temp in our experience.
With it being a suspended floor, how old is your house? Do you know if the joists are spaced apart as per current building regs? If so a spreader plate system like this could be what you want
You could then floorboard directly onto this and then your desired floor finish.
You can also get structural floorboards with pipe grooves in them which would remove the need for the spreader plate above - but the spreader plate would provide a better heat output and keep the finished floor level to near what it is now - if you decide that is important to you.
Also consider just laying this onto your existing floorboards https://www.theunderfloorheatingstore.com/water-underfloor-heating/insulation-boards/john-guest-overlay-boards-floor
Whatever you choose you must insulate between the joists as best you can. 100/150mm rock wool held in place with a netting. To be honest you should do this even if you don’t choose to have ufh.
Finally the difference between a 15mm pipe and a 16mm pipe is about 20% extra cross sectional area (ignoring wall thickness differences), which means 20% more energy down the pipe which makes for a more efficient system.
Personally, I would go with ufh every time. It’s a nice cosy type of heat, your feet will love it and I’m sure jt would add desirability and value to your house.
On a side note tonyg2003 hits the nail on the head. Ufh should be on almost constantly to maintain temperature. The lag times from calling for heat to reaching desired room temp is way too long to work with your current heating regime.
Ufh should be on almost constantly to maintain temperature.
Not our experience. On for 2 hours in the morning (5-7) and 2 hours (4-6) in the evening. This s a wet system (2 circuits) running off an oil fired condensing boiler. Solid floor with 100mm insulation and the pipes set in a 50mm wet screed. The UFH is only in the kitchen area. and the thermostat is set to 17c.
Sorry I wasn’t clear, I don’t mean ‘on’ as constantly kicking out heat, I mean ‘on’ as the system will fire up if the temp drops below the thermostat.
I have mine set at 18 degrees between 5 am and 8pm (‘on’ for 15 hours) and 12 degrees overnight. How many times it actually fires up inbetween those hours I have no idea.
Wunda underfloor. Really good. We did 40sqm for about £600. Ontop of 120mm insulation. It’s really good. Few hrs first thing and evening. Just got plumber to link it to current combi rad system with valve.
Yep our boiler isn’t “on” all the time. Although ours was fitted when the house was built so a bit different from the OP and runs off a large hot water tank. It seems a pretty efficient way to hear the house.
Wunda underfloor. Really good
+1 for Wunda as a supplier. ours has been running 6 years now. Significantly cheaper than any of the other suppliers. The pipe that goes in the floor is all the same quality. Some of their 'above the floor' kit - manifolds and the like - might look a little less slick than their competition but the quality is fine (and the only bits that are actually likely to fail are motorised valves if you use them, and those fail at intervals whoever makes/sells them, and they're cheap enough to replace when they do)
UFH does work much better in a well insulated house, run at a low temperature. If you try to run it like a radiator with 'hot' water then it takes a long while to get hot, and will keep pumping out heat long after you stop pumping water into it (because, if it's in concrete, you've got a big thermal mass of floor). Much less so if it's an 'overlay' system rather than buried in concrete. That means it's hard not to overheat the house as the floor will be hot long after a room thermostat stops calling for heat.
Ours runs 4am to 10pm on a weather compensation controller that varies the flow temperature depending on how cold it is outside which keeps the floor temperature very close to target room temp so no overheating. 11C outside today and flow temp is only 22.5C (actual floor temperature will be lower than that)