Retrofit Underfloor Heating

Apodemus

Chickereeeee said:

Doozergirl said:

ComicGeek said:

1920s detached house - so unlikely to be very well insulated or reasonably air tight.

So you would be very unlikely to get enough heat from UFH to heat the existing house, regardless of the system used. 

Agreed. 

You can't run low temperature heating without your house being capable
of holding onto that heat. 

 

Fabric first.  

But a large proportion of UK housing stock is of a similar build (or worse), and if ASHP are the only option in the near future, what's going to happen? Knock them all down and rebuild?

That's the big question that Government(s) are steadfastly avoiding.  The housing stock is going to need huge investment, with pay-back times well beyond what might be sensible for the individual householder.  At the same time we have a feeding-frenzy from the less reputable parts of the building trade...

Bendy_House

Chicken, your new extension will be to current standards, so should be ideal for UFH. 

The existing suspended floor in the main house will be far less ideal due to the relatively poor levels of insulation in there, including in the floor itself. 

You say the retro system is only 25mm thick? That suggests that the insulation layer under the pipes will be what - 10mm-ish? And that sits on bare floorboards, with no further insulation underneath? It will surely struggle?

We had a 6m x 6m extension built recently, and it's heated by just a couple of 450mm-wide tall designer tubular rads. I chose them simply not to be intrusive, but they certainly won't be able to cope with a 'cool' water supply such as from an ASHP, but, frankly, that wasn't a consideration for me since the rest of the house certainly wouldn't cope with that either.

Anyhoo, you are right to be planning for the future, and your low-temp outputting options would appear to be either UFH, or oversized rads. The latter will be much cheaper, much uglier, but a lot more flexible. Ie, they respond quickly to demand and, if they aren't outputting enough in very cold weather, turn them up. (Tho' an ASHP prob won't cope either)

UFH might turn out to simply not perform as you hoped in your age of building, with its levels of insulation, and then you are stuck with an expensive but inadequate system that will need back-up in colder weather.

If you decide that UFH is not suitable for the main house, then I doubt it'll be worth it for just the extension? So at least plan a way to as unobtrusively as possible fit an oversized rad system that work in there on ~45 (or less) temps. Skirting board rads?

Doozergirl

Chickereeeee said:

Doozergirl said:

ComicGeek said:

1920s detached house - so unlikely to be very well insulated or reasonably air tight.

So you would be very unlikely to get enough heat from UFH to heat the existing house, regardless of the system used. 

Agreed. 

You can't run low temperature heating without your house being capable
of holding onto that heat. 

 

Fabric first.  

Actually the house is pretty good wrt draughts. Double glazed, good loft insulation. The extension would be built to modern standards, of  course, which would mean a couple of outside walls would be 'upgraded'. With a bit of internal insulation, half the house would be to modern insulation standards.The remainder  could have additional insulation added later.

That's my whole point - adding additional insulation later defies the entire point.  People are obsessed with wanting clean lines or just having the latest fancy thing but the question they should be asking is one of two, depending on how much money they have.  

1. How do I make this home contribute towards net zero?  

2. How can I improve this house so I can afford my utility bills?  

Adding a 'bit of insulation' here and 'that can be insulated later' there doesn't cut it.    You need a full envelope to stop your boiler endlessly pumping to replace heat lost - if you aren't producing as much heat (as with UFH), you need to retain more.  

Part of a house that works fine with high temp rads is not going to cope equally well with low temp heating. Putting in a lot of expensive UFH is a risk when we know that more insulation is actually the answer to the right question. UFH is then a lovely thing to have, otherwise it's a fur coat with no knickers and you up with cold nether regions.  

But a large proportion of UK housing stock is of a similar build (or worse), and if ASHP are the only option in the near future, what's going to happen? Knock them all down and rebuild?

This is a far more poignant question than you think it is.  I can tell you what isn't going to happen and that is people living happily with low temperature heating in houses haven't had significant sums of money spent in upgrading the fabric first.    

I sat in a conference last month and the only sensible thing I could come up with was properly valuing houses according to how much work is actually needed.   We could have started addressing this two decades ago when houses were actually
affordable.  People need to stop tinkering around the edges with their 'renovations'.  The housing market needs to be about quality,
not ignorance and maximum profit.  

Also, the common idea with ASHP, As I understand it, is that you could use an existing system, but with larger radiators. Surely existing radiators + wUFH would have a similar output?

Correct.  Except the same problem exists with ASHP.  The gov's current idea of giving people a discount on ASHPs is absurd.  It's a positive headline but ASHPs will not work with houses that haven't also been retrofitted properly with considerable amounts of insulation as a full envelope and properly managed ventilation.  They're totally silent on that.  

Existing systems will also work better with a retrofitted house - begging the question of where the money really needs to be spent.  

I live in a brand new self build, with insulation levels that exceed the new regulations, not just the ones in place a few years back.  We can build up a real sweat with the UFH that is on the ground floor.  We have no heating upstairs.  

Our friends have a lovely, older but fully renovated house with UFH downstairs.  The extended area works with the UFH and south facing windows.  The rest of downstairs is cold and the difference between rooms is noticeable.   The extension door remains closed all winter and I've never sat in the front room.  

There is probably a balance between the two, but UFH of itself is not the thing to be desiring.  

ComicGeek

Chickereeeee said:

Doozergirl said:

ComicGeek said:

1920s detached house - so unlikely to be very well insulated or reasonably air tight.

So you would be very unlikely to get enough heat from UFH to heat the existing house, regardless of the system used. 

Agreed. 

You can't run low temperature heating without your house being capable
of holding onto that heat. 

 

Fabric first.  

Actually the house is pretty good wrt draughts. Double glazed, good loft insulation. The extension would be built to modern standards, of  course, which would mean a couple of outside walls would be 'upgraded'. With a bit of internal insulation, half the house would be to modern insulation standards.The remainder  could have additional insulation added later.

But a large proportion of UK housing stock is of a similar build (or worse), and if ASHP are the only option in the near future, what's going to happen? Knock them all down and rebuild?

Also, the common idea with ASHP, As I understand it, is that you could use an existing system, but with larger radiators. Surely existing radiators + wUFH would have a similar output?

The uninsulated external walls are going to be your main problem, unlikely to get enough heat output from a wet UFH system in the existing part. The UFH output is limited by the surface temperature and the area of the room - radiators aren't limited, you just make them bigger or put more in. The heat output from UFH might only be 60-70 W/m2, so probably a good 20-30% lower than what you might need - then take away those floor areas with fixed furniture, loose furniture, kitchen units etc, and the actual heating area starts to drop further.

Heat pumps in general are the main option in the future, but they come in lots of different forms and system types. The Government has always blindly believed that everyone will be able to simply replace their gas boiler with an ASHP in the future, but the difference in temperature output makes that really difficult.

The really basic thing that the Government has lost sight of is that insulating the existing housing stock really well would not only reduce heating costs and improve comfort but reduce heating demand down to a point where you can just replace the boiler with an ASHP - you no longer need as much heat from the radiators, so don't need to replace them and incur additional costs! 

I would also insulate the existing building as part of the project, as you will absolutely notice the difference in comfort levels between the old and new if you don't. 

Chickereeeee

Some replies are missing my point. OF COURSE insulating the entire house in one go would be ideal, but also would cause enormous mess and disruption. I would prefer to do it when decorating a room anyway. For now, we will keep the existing boiler (or even upgrade it) so existing radiators etc will be fine.

But, if I am adding a new, insulated extension, it makes sense to use a 'future proof' heating system, wUFH, I would think. If I am doing that, I could add retrofit wUFH (IF it works) to the rest of the ground floor. THEN, I could insulate rooms and migrate to ASHP in the future.

What I don't know is, if is possible to run wUFH and traditional radiators off of the same boiler, and how well wUFH works.

I guess the three options for the extension are wUFH only 2) radiators only 3) both systems.

ComicGeek

Chickereeeee said:

Some replies are missing my point.

Not really, as it's always easier to do the work when you're living in the mess and disruption of the extension works already - difficult to do it later, and insulation is such an essential thing.

Forget about wet UFH in the existing part if you're not going to insulate it now, it won't work. The water temperature in the UFH is the same regardless of whether it's from a gas boiler or ASHP, it's limited by being in the floor. You need to either insulate now and install UFH, or insulate later and keep the existing rad for now.

So wet UFH in the extension is future proofed anyway - or you could size the radiators in the extension based on a lower temperature. Or you work on the basis that in 10-15 years there will likely be other alternatives you could implement.

Yes, you can run wet UFH and traditional rads off the same boiler, but you would want a dedicated heating circuit for each so you could control each separately. I personally wouldn't have half the ground floor as UFH and half as rads as the 2 are completely different control strategies, but people do it.

I personally hate UFH, as I much prefer the quick response of radiators. But a lot of our clients love it. Personal choice.

Apodemus

ComicGeek said:

Chickereeeee said:

Doozergirl said:

ComicGeek said:

1920s detached house - so unlikely to be very well insulated or reasonably air tight.

So you would be very unlikely to get enough heat from UFH to heat the existing house, regardless of the system used. 

Agreed. 

You can't run low temperature heating without your house being capable
of holding onto that heat. 

 

Fabric first.  

Actually the house is pretty good wrt draughts. Double glazed, good loft insulation. The extension would be built to modern standards, of  course, which would mean a couple of outside walls would be 'upgraded'. With a bit of internal insulation, half the house would be to modern insulation standards.The remainder  could have additional insulation added later.

But a large proportion of UK housing stock is of a similar build (or worse), and if ASHP are the only option in the near future, what's going to happen? Knock them all down and rebuild?

Also, the common idea with ASHP, As I understand it, is that you could use an existing system, but with larger radiators. Surely existing radiators + wUFH would have a similar output?

...reduce heating demand down to a point where you can just replace the boiler with an ASHP - you no longer need as much heat from the radiators, so don't need to replace them and incur additional costs! 

...but you will need to reinstall a hotwater tank if you are migrating from a combi!

Chickereeeee

Apodemus said:

ComicGeek said:

Chickereeeee said:

Doozergirl said:

ComicGeek said:

1920s detached house - so unlikely to be very well insulated or reasonably air tight.

So you would be very unlikely to get enough heat from UFH to heat the existing house, regardless of the system used. 

Agreed. 

You can't run low temperature heating without your house being capable
of holding onto that heat. 

 

Fabric first.  

Actually the house is pretty good wrt draughts. Double glazed, good loft insulation. The extension would be built to modern standards, of  course, which would mean a couple of outside walls would be 'upgraded'. With a bit of internal insulation, half the house would be to modern insulation standards.The remainder  could have additional insulation added later.

But a large proportion of UK housing stock is of a similar build (or worse), and if ASHP are the only option in the near future, what's going to happen? Knock them all down and rebuild?

Also, the common idea with ASHP, As I understand it, is that you could use an existing system, but with larger radiators. Surely existing radiators + wUFH would have a similar output?

...reduce heating demand down to a point where you can just replace the boiler with an ASHP - you no longer need as much heat from the radiators, so don't need to replace them and incur additional costs! 

...but you will need to reinstall a hotwater tank if you are migrating from a combi!

It's a pressurised system!

Chickereeeee

ComicGeek said:

Chickereeeee said:

Some replies are missing my point.

Not really, as it's always easier to do the work when you're living in the mess and disruption of the extension works already - difficult to do it later, and insulation is such an essential thing.

Forget about wet UFH in the existing part if you're not going to insulate it now, it won't work. The water temperature in the UFH is the same regardless of whether it's from a gas boiler or ASHP, it's limited by being in the floor. You need to either insulate now and install UFH, or insulate later and keep the existing rad for now.

So wet UFH in the extension is future proofed anyway - or you could size the radiators in the extension based on a lower temperature. Or you work on the basis that in 10-15 years there will likely be other alternatives you could implement.

Yes, you can run wet UFH and traditional rads off the same boiler, but you would want a dedicated heating circuit for each so you could control each separately. I personally wouldn't have half the ground floor as UFH and half as rads as the 2 are completely different control strategies, but people do it.

I personally hate UFH, as I much prefer the quick response of radiators. But a lot of our clients love it. Personal choice.

To your first point: I think the plan for the extension can be kept fairly isolated from the rest of the house, for most of the work anyway. The bit that cannot be is the floor, as it would be continuous with the existing kitchen, which is tiled, as is most of the ground floor. 

To you last point: I have read that, as retrofit wUFH is surface-mount, it also responds quickly, as there is no slab to heat. The extension would take longer, unless surface mount wUFH  was used there as well.

onomatopoeia99

I have the "polypipe overlay" system in my kitchen as a retrofit under 10mm slate tiles and a layer of 6mm hardiebacker.  I could only get 12mm insulation between the slab and the boards the water pipes run in without introducing an excessive step, and being a 70 year old house the slab is not insulated.  It works, it heats the room, feels lovely underfoot and though I replaced the 1800mm long type 21 radiator with a vertical radiator just in case the UFH needed assistance, in the 7 years since I replaced the kitchen I've not needed it even in January and February.

For reference since everyone is talking about insulation, I installed 275mm rockwool  in the loft (which had about 30 binbags worth of polystyrene chippings when I moved in, so nothing) and the wall cavities have been insulated, which is about as far as I can go without massive disruption (e.g. digging out the slabs and insulating them).  I can run my radiators in the rest of the bungalow at 45C but have to leave the heating running all day during the week as it takes considerably longer to get up to temperature that way.