UFH - is it actually a good idea or not

[Lord Greyabbey]

UFH - seems to be all sorts of stories, experiences, viewpoints out there on this one, so please help me decide.

 

Background: planning a new 1.5 storey 2500sq ft timber frame house with concrete upper floor.

 

I'm not actually averse to radiators in a room as it's what I am familiar with, and we presently have a 100 year old house with 20+ cast iron radiators which are both a nice feature, give out great heat and are handy for drying clothes on!  (Yes I know, but we do)

 

UFH - seems complicated, a lot of buried stuff that if there is fault means difficult (expensive) remediation works and having had a copper pipe leak in a concrete slab before, I'm very aware of the hassle that causes, plus time to heat up/cool down the slab seems to be a common gripe.

 

At the same time I need to hit a SAP rating of 88+ for our Ecology mortgage.

 

Question is:

 

1. Is UFH just a given these days for a modern eco home?  i.e. suck it up and get on with it, quit worrying about nothing; or

2. Is the old school approach of radiators on the walls actually a feasible option in this day and age?

[SteamyTea]

19 minutes ago, Lord Greyabbey said:

UFH - seems complicated

Probably less complicated than a radiator system.

20 minutes ago, Lord Greyabbey said:

a lot of buried stuff

Less than a radiator system, unless you surface mount all pipework.

 

21 minutes ago, Lord Greyabbey said:

plus time to heat up/cool down the slab seems to be a common gripe.

Pump in enough energy (heating), or pump out enough energy (cooling) and that problem vanishes.

 

I think you may be confusing the thermal distribution system i.e. UFH, radiators, forced air, with the heat source i.e GSHP, ASHP, oil burner, gas boiler system (2 types) etc.

 

Get a proper thermal model done at the design stage, this will include the appropriate amount of insulation for UFH, and an air change target i.e. Less than 1.5.

 

The better, thermally, you make your house perform, the smaller the heating system needed.

Small problems are easy to solve.

[Indy]

I'm in a similar boat to you - new build house though with concrete walls and most likely concrete floors. However, I'm much more pro UFH as I hate radiators - mainly for the space they take up on walls and the fact that you can't really use that space for anything else.

 

I did also have questions around maintenance of UFH, especially if you're burying these within your concrete slab. The conversations I've had with loads of people assure me that failures are quite rare, and probably no more messy than sorting radiator pipework.

 

The bits I haven't completely figured out are whether we go for UFH throughout (i.e. on the upper floors as well), how to use the ASHP + UFH for some sort of cooling effect and finally, wet UFH vs electric UFH in the bathroom areas.

Edited May 25, 2022 by Indy

[jayc89]

We live in a 150 year old house (crap air tightness, insulation etc etc). When renovating we chose to replace the rads with UFH and don't regret it. 

 

The only inaccessible part should be the loops, which should be continuous so very little to go wrong once the slab/screed's poured. I think the life expectancy of most UFH pipe is 100 years +

 

We also find the rooms to be a nicer type of warmth, less stuffy. 

 

I don't think there's any reason why you couldn't build with rads, but I don't think there's good enough reason to do so either.

 

In theory, a well insulated new build with the even distribution of heat that UFH provides should mean that you don't need any active heating upstairs at all. 

Edited May 25, 2022 by jayc89

[nod]

We weren’t sure if to have UFH 

Lack of space under low windows decided us 

It was the first thing on our tick list for our next build 

[SteamyTea]

1 hour ago, nod said:

Lack of space under low windows decided us 

Assuming that was going to be the location of a radiator, why would you fit on to an external wall.

[Dreadnaught]

Perhaps think of it a different way. Think of UFH as having radiators the size of the floor. Such large "radiators" gives some distinct advantages.

 

The circulating water can be a lower temperature for a given room temperature, which is helpful for an ASHP (now or as an option for later).  

 

The even infrared warmth that comes from across the entire floor is more pleasant than (hotter) radiators producing convection drafts.

 

UFH when combined with an ASHP offers the option of cooling in summer. Can't do that with radiators.

[Gone West]

4 hours ago, Lord Greyabbey said:

UFH - seems to be all sorts of stories, experiences, viewpoints out there on this one, so please help me decide.

In my view UFH should be banned in building regs until standards reach PH. All the effort that is put into insulating walls and ceilings and then you are allowed to waste heat by putting it into the ground. Even if all houses were truly built to current regs and building inspectors checked rigorously the standards are not yet high enough to have the slab at a low enough temperature to minimise heat loss to the ground. When building standards are better than PH then wet heating isn't needed.

[joe90]

18 minutes ago, Gone West said:

you are allowed to waste heat by putting it into the ground.

Surely this depends on the amount of insulation used?, plus the fact that the insulation factor of the house itself stopping the ground from being chilled by winds etc?

[SarahG]

I’ve also been thinking about this. My in laws renovated their house and put in UFH. It’s hot and stuffy and we find it quite unpleasant. This has led my OH to think he doesn’t want UFH and wants to bring some of our old cast iron radiators with us and just stick with them. Which we like for similar reasons as others. We do however want ASHP and I’m not convinced this will work with radiators. We are going brick and block for our build.

[Jilly]

I love our UFH. You can run the room thermostat lower and the floor will work with low temp water, such as from an ASHP. We are on LPG at the moment but run it at 45 degrees (hasn't been needed since April). We didn't use a decoupling mat which apparently can reduce the efficiency (you'll get into another rainforest of screed drying time worries), and put fancy insulation under the slab as we couldn't get the recommended (on here) of 200mm (building regs is less). 

[jayc89]

50 minutes ago, SarahG said:

I’ve also been thinking about this. My in laws renovated their house and put in UFH. It’s hot and stuffy and we find it quite unpleasant. This has led my OH to think he doesn’t want UFH and wants to bring some of our old cast iron radiators with us and just stick with them. Which we like for similar reasons as others. We do however want ASHP and I’m not convinced this will work with radiators. We are going brick and block for our build.

 

Interesting - our experience is the exact opposite (rads were hot and stuffy), UFH lovely.

 

Rads can work with ASHP, but because the flow temp will be lower, you need larger rads for the same size room (approx 150% the size standard radiator calculators would recommend)

[Iceverge]

52 minutes ago, SarahG said:

It’s hot and stuffy

 

It sounds more like a ventilation issue. 

[JohnMo]

Or they need to turndown the thermostats and/or the flow temperature at the manifold.

 

We have UFH, it gives a very even spread across the whole house all the time.  Basically don't operate like a radiator system, lots of on off cycles as you are wasting energy.

 

Two modes of operation, chunk heating, a few hours to charge the floor, then leave the heat to slowly release or very low temperature for a long time.  We tried the later first, but with well insulated houses the normal manifold mixers don't turn down low enough.  We tried min setting at 28 degC and overheated somewhat.  So went to chunk heating 6 hours at 30 degC which worked fine.

 

Have made mods for next heating season, so I can reliably get to any temp I want, maybe somewhere close to 24/25 flow temp.

[jack]

1 hour ago, SarahG said:

I’ve also been thinking about this. My in laws renovated their house and put in UFH. It’s hot and stuffy and we find it quite unpleasant. This has led my OH to think he doesn’t want UFH and wants to bring some of our old cast iron radiators with us and just stick with them. Which we like for similar reasons as others. We do however want ASHP and I’m not convinced this will work with radiators. We are going brick and block for our build.

 

A few years back I went to a friend's house who'd just finished a full-on gut and renovate. They'd put in UFH on the ground floor, and basic building regs insulation with little attention to airtightness. I found their house to be uncomfortably warm, at least partly due to the blood in my feet boiling from being in contact with the hot floor.

 

If you have decent insulation, you only need to run your UFH at a relatively low temperature. In my case, I've turned down our ASHP to the lowest temperature it can do (25 deg C), and that works just fine in all but the very coldest weather. The polished concrete floors are extremely comfortable in winter, and pleasantly cool during those periods of summer when the ASHP is run in cooling mode.

 

As someone else said, the stuffiness could also be a lack of ventilation. MVHR will help with that. 

[jack]

7 hours ago, Lord Greyabbey said:

1. Is UFH just a given these days for a modern eco home?  i.e. suck it up and get on with it, quit worrying about nothing; or

2. Is the old school approach of radiators on the walls actually a feasible option in this day and age?

 

1. Yes.

2. Possibly feasible, but from my point of view is mostly a set of drawbacks. 

 

I actually had a leak in our UFH shortly after we moved in. It appears that an electrician who was asked to do something at the last minute before the polished concrete floor was laid accidentally drove a screw into an UFH pipe. I dug out the concrete around it and fitted in a loop of UFH pipe using joints. It's been over 6 years since then and no problems.

 

That said, this leak was relatively easy to find, because it was right near a recess for a socket (which is why the electrician was involved). If you had a leak buried in concrete you'd have more of an issue finding it, but the real question would be what would cause such a leak? There are no joins if you do it properly. There's very little thermal stress given you're running low temperatures. I can't really see what would be likely to cause a failure.  

[recoveringbuilder]

We put ufh in our build in 2008 , when we sold it and bought another house that was the first time I gave it any thought. I had never realised how good it was until we went back to radiators, it was a definite in the next build 

[Nickfromwales]

14 hours ago, SarahG said:

My in laws renovated their house and put in UFH. It’s hot and stuffy and we find it quite unpleasant.

Then its the wrong solution for that dwelling. You should not feel anything like that in a house with a correctly designed and executed UFH installation. UFH flow is obviously running way too high, but is probably doing that to keep the rooms at temp.

See if they can make some improvements to the house to reduce the amount of heat that the UFH then has to provide?

[Gone West]

14 hours ago, joe90 said:

Surely this depends on the amount of insulation used?

Well the more insulation that is used the better, but no insulation is perfect so IIRC even with 300mm EPS Jeremy calculated an 8% heat loss to the ground.

 

14 hours ago, joe90 said:

plus the fact that the insulation factor of the house itself stopping the ground from being chilled by winds etc?

The area under the insulation won't be chilled by winds and should reach a steady state which would just be a higher temperature than without UFH.

[JohnMo]

Expanding on Gone West comments

 

The maths for downward heat loss in simple terms is

 

Equation.

U value, multiplied by area, multiplied (flow temp of water - ground temp below floor).

 

For a given flow temperature.  Poor u value, lost heat downwards is higher than upward heat transfer to room. To compensate the flow temperature is increased. Good u value downward heat loss is low more heat to room. To compensate flow temp is decreased.

 

Troubles come with poor u value, as your downward becomes large, so to get a suitable heat supply to the room you have to flow at a higher temperature, (as too much heat energy is going down) which further increases your loss downwards. (flow temp of water - ground temp below floor) this part of the equation becomes larger.

 

In simple terms that means a u value of 0.1 or better, flow temp mid 20s, 0.2 u value, flow temp could be in the 40s for same conditions outside the floor area.

[SteamyTea]

19 minutes ago, Gone West said:

Well the more insulation that is used the better, but no insulation is perfect so IIRC even with 300mm EPS Jeremy calculated an 8% heat loss to the ground.

This is the problem of using percentages.

If he had left the door open then that decimal fraction may have dropped to 2%.

 

There is also a case of how it is measured.  Is it a decimal fraction of all losses, all losses minus any gains (solar), losses only when the heating is on, all losses only during the heating season, regardless of heating system on/off state.

Then it has to be correlated with temperature differences between the OAT, IAT and GT.

 

Much easier to estimate the actual losses, when heating, to the ground i.e. 5 W.m^-2 or 50 kWh.year^-1.

 

In statistics, first question is 'is it a large number'.

 

[joe90]

1 hour ago, Gone West said:

Edited May 26, 2022 by joe90

[SarahG]

1 hour ago, Nickfromwales said:

Then its the wrong solution for that dwelling. You should not feel anything like that in a house with a correctly designed and executed UFH installation. UFH flow is obviously running way too high, but is probably doing that to keep the rooms at temp.

See if they can make some improvements to the house to reduce the amount of heat that the UFH then has to provide?

Think they are too old now to change anything! We just have to accept it’s not pleasant for us when we go round. I am confident I still want UFH here and that it is the right solution. Just need to persuade my husband that it’s their setup that is incorrect and not the UFH! Thanks for the tips all.

[Indy]

For those that have used UFH in their builds, do you use the same wet UFH throughout or do you split the bathrooms to have electric UFH (i.e. switch on when needed)?

 

Also, I assume that each room temperature is controllable using dedicated thermostats or can you only have 1 temperature set at the master control and through the house?

[SteamyTea]

8 minutes ago, SarahG said:

We just have to accept it’s not pleasant for us when we go round

Is it pleasant for them?

 

My Mother's house is at about 78 F 25.5°C.

Way to hot for me most of the time, but if I am just sitting down and reading it is lovely.