How does it work if you live in a highly-insulated modern house with wet UFH and you’re using the hob or the oven or the expensive and completely unnecessary stove you agreed to in the interest of a quiet life?

Presumably each space has its own stat, which will close the motorised valve to that zone? The floor will remain warm for several hours while you run around opening windows and skylights then resume later that night when the temperature stabilises?

Does it harm the system to be turning the valves on and off?

Another question: how does a geothermal system heat water for baths and showers etc.? Is that by direct feed off the refrigeration compressor thingy?

Stop fretting. It’ll all go to pot when the mice eat through the control wires anyway.

On your first question, yes. It is exactly as you described, for is on a separate heated zone. We’ve recently had an extension and got big open plan kitchen living room at back of house. Super insulated and clichéd stove. Not used either heated floor or stove yet as it is so loaded with insulation

We put wet underfloor into our annex when we renovated it.

Each room/zone has a thermostat. You set the temp and then it open/closes the value for the piping below.

If your oven/hob is on for that long and gives out that much heat for that long – are you a restaurant?

And as for stoves, should be banned from modern house IMO.

Oh, ours is electric (no mains gas), ain’t cheap to run – but, my aged Mum lives there so it’s as warm as it needs to be.

If your oven/hob is on for that long and gives out that much heat for that long – are you a restaurant?

Could be one of those lifestyle agas.

We’ve got wet underfloor heating in a virtually zero insulation 300 year old house. It’s different to traditional radiators and once you’ve used it for its initial few hours (maiden voyage) it’s actually lots quicker than the radiators to warm a whole room. A 1 degree rise takes about 10 minutes but is noticeable quicker – the whole floor is your heater.

Yes, each area/room has its own thermostat.!if the cooker/oven has been on then the heating shuts off – it seems to be far more sensitive to small temp variations than the old system. It stays warm for a while, but look at this as more of a stable temp’ with fewer fluctuations than what you’d have with a radiator system. Of course, this is only my personal experience based on my system in my house.

I know nothing about geothermal but if I had the money that’s where I’d be looking. Though gas is still relatively cheap, fossil fuels are history (or should be).

I know nothing about geothermal but if I had the money that’s where I’d be looking. Though gas is still relatively cheap, fossil fuels are history (or should be).

Aye, but what happens when we’ve sucked all the heat from the planet eh? eh?

Another question: how does a geothermal system heat water for baths and showers etc.? Is that by direct feed off the refrigeration compressor thingy?

The domestic hot water is normally heated through some kind of heat exchanger allowing heat to be transferred from the heating water into the DHW. Commonly a “tank in tank”, the DHW tank is surrounded by the space heating water and absorbs heat from the space heating water through the walls of the inner tank. But you usually have an immersion heater in there too cos the space heating water isn’t hot enough to kill off Legionaires, so the immersion comes on once a day for a bit to bring the DHW up to 60°+ for an hour or so.

We have geothermal/UFH, had it for about 12 years and still not certain how it functions in some circumstances.

Each zone/room has a thermostat except the bathrooms which heat whenever the heat pump is working, i.e. if one or more zones is open. The system is not timed to operate and relies on the thermostats to switch on and off, this uses the concrete floors as heat stores to maintain and avoids repeated heating and cooling of the floors.

Hot water is provided using a large storage tank. This is heated 3 times a day by the heat pump, hot water then is drawn from a heat exchanger which heats incoming water supply as required and recirculates to the tank.

We have a wood-burning range cooker in the kitchen but haven’t used it for some years as it makes the room uncomfortably hot.

It is very expensive to run on electricity but the alternative would be oil or gas which we don’t have. Upside, the house is generally warm.

Wet UFH is very good. We’ve got it in out extension. Wish we had it throughout. Initially we had a pretty dumb thermostat that was just active 24/7 but I replaced with a Nest E, so in learning mode susses out when you want heat and has a wet UFH mode so takes into account the thermal lag and if its more efficient to turn off for a few hours or to just keep it chugging on. The rest of the house is on a separate more conventional system with its own stat. We did originally plan to have a wood burner but glad we didn’t as the UFH is plenty warm enough. I guess I do miss something with a single heat source because as you walk into the room from the cold outdoors, though its warm you miss that single hot heat source of a fire to warm your cheeks on…but the room is plenty warm enough. Its the warmest part of the whole house. I could crank it up and if cranked up with the doors open could heat up the whole house, but I’m stingy with the thermostats so keep it at a sensible 18 degrees.

It’s very efficient. the floor will be nice and toasty and the boiler is hardly on. I guess you’re only really heating the water upto about 35 degrees C so the boiler doesn’t need to be on for long to heat up the water, circulate it and warm up the screed floor. There is a bout a foot of insulation beneath the UFH pipes to prevent heat loss into the foundations and the roof is packed with about 2 foot of insulation so nice and toasty.

Mate has geothermal…heats the water in the storage tank to about 55 or so degrees then you top up with an electric emersion heater. It’s a very electricity hungry system so unless you have solar or something then it’ll cost you in electric. His house was quite big…a converted barn, so had to have a dedicated 3-phase supply installed costing about £30k alone. And he installed a wind turbine in a field to power it and sell excess back to the grid. With it being such a big house I guess all that investment pays off eventually, but not so sure in a normal sized house it would be economically viable unless it was a new build. But I guess technology might have moved on since he built his home.

Interesting thanks.

Our dogs love it. They find the warmest spots and won’t move!

If I was building from Scratch I’d put it in communal areas but I think it might be overkill in bedrooms where generally it should be cooler all year round

Buy two baths, put coal in one, use the other for washing your feet.

Depends what you mean by highly insulated modern house. Highly insulated, air tight house with mvhr = ufh on ground floor only run at a low temperature all as one zone and it will only come on occasionally and you will never use your wood burner.Geothermal does not make sense in a normal sized single modern house. Air source heat pump would be a much better bet. Geothermal is popular for massive country homes that have a pretty average level of insulation and require massive amounts of cheap energy to heat them.

We did a refurb where we extended a little and made a large open plan kitchen/diner/living area. Despite good insulation in the new bit we have lots of glass (big windows, sky lights and patio doors) and lose heat to the rest of the house via 3 doors. We have 2 UFH zones (kitchen and hall/utility) which allows us to have the hallway a little cooler.

We also installed a 5Kw stove in the big room which was a very good idea. It adds an extra bit of atmosphere and heat when it gets cold. Can’t beat firing it up on a frosty Sunday morning or when you get back from a cold walk in the afternoon.

Note ours is ‘overlay ufh’ (low profile stuff) so it heats up a bit quicker and cools down quicker than if is was all buried under a deep slab with loads of insulation below that. This is beacuse most of the floor area was an existing slab.

To summarise its great. Just popped down to make some toast and feeling the warm floor on my delicate tootsies is lovely. No issues with over heating in our place. As others have suggested it depends how you define ‘super insulated’ and how the system is specced.

Good luck.

We’ve had a “Wunda” system fitted when we had our kitchen/diner redone last winter.

Works great. It taps off the standard heating circuit from the Combi, measures it’s own feed/return temperatures and only mixes in additional hot from the boiler when required.  Temperature of the floor is basically controlled by the boiler/Radiator temp so now run the whole system cooler (c40 degrees as opposed to 50-55 degrees for rads alone).  Also needs to be on for longer to account for warm-up time but fundamentally once warm teh boiler only draws gas for a few seconds every 5-10 min, so really doesn’t seem to use that much gas.   We fitted 20mm insulation board with 20mm limestone tiles on top so it takes a little while to warm up but stays warm with little further input.

Pipe is laid in insulation board that is fitted on top of existing flooring.  So it cuts off access to your underfloor areas from above, but we’ve only got it on solid floors so there’s no wires/cables in there anyway.

Would definitely fit it throughout the ground-floor if I could afford it, as it would also effectively insulate and draft-proof our leaky 120 year old floor-boards!

By preference I would also run it off a thermal store by preference, heated by a combination of solar thermal and stoves.  But the installation cost and disruption would be prohibitive in a family home without a south-facing roof.   Then switch all the pumps/controls to 12V supply, run off a battery bank charged by solar PV to take the whole system entirely off-grid.  It means should there be a power cut in the depths of winter, you can still be warm and have hot water!  Probably only sensible in a rural new-build….

Keithb If your boiler is only heating the ufh for a few seconds every 5-10 minutes it is short cycling which is not good for the boiler and very inefficient.You need a buffer tank.
You also can’t heat ufh off solar thermal or pv as there tends to be not much sun at the time of year you need the heating on.

Only come across it once, in an AirBnB.

We turned it on in the evening. It didn’t seem to do anything for ages. Got up in the middle of the night for a pee and the floor was nice and warm*. I wasn’t exactly sold!

*because of the UFH, not because i peed on it

Have it in the bathroom.

Surface mounted Wet pipe on low profile gypsum board system hooked up to a hidden thermostatic radiator valve.

Works great.

Didn’t see what an expensive manifold brought to the party in this case

Well if you hooked it upto a radiator then no wonder it works great. A proper UFH system the water is alot lower temp, around 40 degrees and not the 60 or so degrees the water in your rads are at. Which is why they’re so efficient. The manifold enables the UFH circuit to be controlled independently of the rest of the system. Your aim is to heat up the screed the pipes are in rather than act as a radiator on the floor.

Manifodls are not expensive – just a bit of pipework. If you’re getting UFH installed as part of a build then the cost is just cheap plastic pipework and the manifold, a pump, zone valve and that’s it. It added FA cost to my extension build. Obviously alot more expensive if you are looking to retrofit. I guess the thermostatic rad valve works but the water going through the system is alot hotter which may or may not be an issue long term.

We turned it on in the evening. It didn’t seem to do anything for ages. Got up in the middle of the night for a pee and the floor was nice and warm*. I wasn’t exactly sold!

Yeah, they’re not heat on demand. Takes a couple of hours to crank up.

We have it by accident in the place I rent at.
It is only in the bathroom where the hot water runs to the shower and the huge towel rail.
It makes winter mornings a lot more pleasant.

The manifold enables the UFH circuit to be controlled independently of the rest of the system. Your aim is to heat up the screed the pipes are in rather than act as a radiator on the floor.

You don’t seem to understand the system I have in the slightest. But don’t let that stop you trying to tell me it’s wrong.

We have it in our house ground and first floor, put in when the first owners had the house built. There is a thermostat in every room even the smallest loo. It works really well – very consistent heating but the house is built on a single concrete slab which and very well insulated too (no heating on all summer/autumn). We weren’t sure that we’d like it when we bought the house 2.5yrs ago but we really like it now.

We have it 8 zones of control. The upstairs lounge has a 6kw stove in it.
We just set that zone to 18c max and light the stove. If we don’t want to light the stove then we can boost the heating.

6kw tops up a room that’s 4*9 pretty easily.

Given you want atmosphere no necessirly heat perhaps soft wood instead of hard wood to drop the power down a bit.

perhaps soft wood instead of hard wood to drop the power down a bit

Same calorific value I believe.
Softwood generally burns quicker than hardwood but they put out the same heat.

Either way – I guess the point is we just set the room a bit cooler and top up.

On a slight tangent, we came across heated skirting board when doing up our place last year.
Due to our irregular shaped rooms it was starting to get too pricey for us, but would have avoided conventional radiators which always seem inconveniently placed, wherever you put them.
UFH was out for us on cost and timescale and not being suitable for the whole house.

Edit – https://www.discreteheat.com/thermaskirt/products-and-information/overview.aspx it’s powder coated too, so shouldn’t need to paint it either, I hated painting a whole house of skirting board in one go.

You don’t seem to understand the system I have in the slightest. But don’t let that stop you trying to tell me it’s wrong.

Well you need to learn how to write and explain yourself better and comprehend what others are telling you based upon what you are telling them…but don’t let that stop you.

I interpreted that you are running your UFH from your rad system which means the hot water is alot hotel than a conventional UFH system. Wrong or right?

I interpreted that your system is surface mounted rather than buried in a depth of screed so the primary source of heat is from the heated pipes like a conventional radiator rather than heating up a block of screed and using the thermal mass of that screed as the main heat source. Wrong or right?

I interpreted that you were controlling it from a conventional rad valve so only on or off with the rest of your radiator system that is different to what a manifold does so cannot take into account the temp lag like a proper UFH system can. Wrong or right?

We’re having UFH downstairs and conventional radiators upstairs, using an air source heat pump on the new house (strip foundations poured this week). We’ve ditched the solid fuel stove as it would just be an expensive ornament. Looked at ground source heat pump + MVHR but view was that it would take decades to recover the extra outlay even though it’s on a Scottish island. As said by others, UFH works by heating the whole floor slab which acts as a heat store / massive radiator.

We’ve ditched the solid fuel stove as it would just be an expensive ornament.

Ok fair enough – but relying solely on AS in a house on a Scottish island is a ballsy move. What do you do if there’s a power cut?
(obviously an extended cold period can be negated with electric heaters)

dovebiker mvhr is more about air quality and reducing moisture build up than recovering heating cost. You will be wanting a decent level of air tightness in a new home heated by a heat pump, especially in that part of the world. If you don’t deal with correct ventilation you will end up with damp problems. Hopefully you have had advice from someone that know what they are talking about (most don’t).

Depends what you mean by highly insulated modern house. Highly insulated, air tight house with mvhr = ufh on ground floor only run at a low temperature all as one zone

This is the right answer, but not what UFH specifiers in the UK will try to install as they’re used to putting it into poorly insulated older houses.

When we were doing our self-build I did a lot of research and had low temp single zone recommended and the more I read up the more convinced I was but basically had to self-specify.

Ours is not quite like that – we did install on the upper floors as well but it mostly turned off and just running in the bathrooms (and my office). The Ground floor is concrete e and runs totally off weather compensation and only an external thermometer – there are no room stats at all. Flow temperature is on a curve increasing as it gets colder outside but the floor is usually only a few degrees warmer than the desired room temperature so you don’t get any overheating due to more people or cooking (Delta between floor and room lessens if the internal temp increases so it’s self regulating)

Based on uncle-in-law who has high insulation, pellet burner, UFH when you use the open fire you sit around in a t-shirt sweating and trying to keep yourself hydrated as it’s completely overkill and uncontrollable in a well insulated airtight house.