Hi,
I am thinking to refurbish a first floor flat with screed floors and
install water underfloor heating. I know that I have to raise floors
around 10 cm but the height between floor and ceiling is just 235 cm.
Has anyone had the same problem ? Would you suggest to go on with the
project ?

Thank you,
Mirco

Mirco Simoni wrote:
Hi,
I am thinking to refurbish a first floor flat with screed floors and
install water underfloor heating. I know that I have to raise floors
around 10 cm but the height between floor and ceiling is just 235 cm.
Has anyone had the same problem ? Would you suggest to go on with the
project ?

I would actually.

In this case I would actually go for a raised timber floor. Less messy
than screeding and you wont get away with 10cm with screed plus
necessary isluation either.

I reckon 2.2m is the minimum room height..beware friends who are 6'8"
tall though ;-)

If you want more than half the heat to go into your flat, not the one
downstairs, use about 50mm of celotex as a minimum, or one of these
proprietary foam mouldings to carry the pipes, and follow manufacturers
recommendations.

Here is a typical, but by no means the only, product

http://download.polypipe.com/bp/brochures/overlay.pdf

I reckon that fits your bill pretty much. Tile your bathrooms and
kitchens, and hardwood your living areas...and laminate the bedrooms!


Also, despite heatloss calcs, go for at least 100W/sq meter. UFH is
great if you have large empty rooms that are tiled: Its a loss less
effective under sofas and rugs. With a thin floor and with wood, you
don't want too much local heat, so LOTS of pipes..cram them in. Its easy
enough to turn UFH down, Its very hard to turn it up.

Another point: you cannot and should not go for more than about 50C
outflow temps on the CH circuit. Normally this means a temp reducing
valve which costs. HOWEVER consider running the whole boiler at lower
temps - it will be more efficient, and if hot water needs to be hotter,
use am immersion heater in the tank as well.

IF its a small flat, one thermostat is enough, and then balance
individual rooms for desired result. If its large or has areas you dont
use, consider zoning it.

Be prepared for very long warm-up times. Although a timber floor is
vastly better than screed in this rep sect , and set any timer
accordingly. This is another reason to have high pipe density..things te
warmer faster.








Thank you,
Mirco

On Thu, 11 Jun 2009 16:16:35 +0100, The Natural Philosopher wrote:

Another point: you cannot and should not go for more than about 50C
outflow temps on the CH circuit. Normally this means a temp reducing
valve which costs. HOWEVER consider running the whole boiler at lower
temps - it will be more efficient, and if hot water needs to be hotter,
use am immersion heater in the tank as well.

You can roll your own proper themostatic mixing system for approx £100 with
a UFH mixing valve (from Toolstation) pump and cylinder stat (or two: one
as overheat cutout) and handful of fittings. Well worth the efort for a
smaller installation.

--
John Stumbles -- http://yaph.co.uk

Just because you're paranoid doesn't mean they're not out to get you.

On 11 June, 15:17, Mirco Simoni wrote:
Hi,
I am thinking to refurbish a first floor flat with screed floors and
install water underfloor heating. I know that I have to raise floors
around 10 cm but the height between floor and ceiling is just 235 cm.
Has anyone had the same problem ? Would you suggest to go on with the
project ?

Thank you,
Mirco

DEFINETLY NOT

DONT FORGET THAT DOORS WILL ALSO BE 10cm SMALLER.

"YAPH" wrote in message
...
On Thu, 11 Jun 2009 16:16:35 +0100, The Natural Philosopher wrote:

Another point: you cannot and should not go for more than about 50C
outflow temps on the CH circuit. Normally this means a temp reducing
valve which costs. HOWEVER consider running the whole boiler at lower
temps - it will be more efficient, and if hot water needs to be hotter,
use am immersion heater in the tank as well.

You can roll your own proper themostatic mixing system for approx £100
with
a UFH mixing valve (from Toolstation) pump and cylinder stat (or two: one
as overheat cutout) and handful of fittings. Well worth the efort for a
smaller installation.

Cylinder stata? Prey tell.

On 11 June, 15:17, Mirco Simoni wrote:
Hi,
I am thinking to refurbish a first floor flat with screed floors and
install water underfloor heating. I know that I have to raise floors
around 10 cm but the height between floor and ceiling is just 235 cm.
Has anyone had the same problem ? Would you suggest to go on with the
project ?

Thank you,
Mirco

No, ceiling will be too low, nobody will want to live there.
Says, I, having just returned from staying at a house with 10 foot
ceilings.
Sadly, my house only has 8 foot ceilings, and it seems slightly
oppressive to me now.
I'm a shade under 6 feet tall.
At 225cm, you'd be walking into light fittings.
Simon.

On Fri, 12 Jun 2009 13:36:08 +0100, Doctor Drivel wrote:

Cylinder stata? Prey tell.

You mean "stats" and "pray"?

One to switch the UFH pump on when the flow from the boiler is hot
enough to be worthwhile, another as an overheat to cut out the pump if the
flow temperature is too high.

This is of course for a set-up where the UFH is not being run as a
separate zone. Yes I know UFH takes longer to warm up so it should be a
separate zone with its own time & temp controls: this is the budget
system. If it is a separate zone then you just have the overheat stat,
wired to close the zone valve.



--
John Stumbles -- http://yaph.co.uk

I used to be forgetful but now I ... um ....

Simon wrote:
On 11 June, 15:17, Mirco Simoni wrote:
Hi,
I am thinking to refurbish a first floor flat with screed floors and
install water underfloor heating. I know that I have to raise floors
around 10 cm but the height between floor and ceiling is just 235 cm.
Has anyone had the same problem ? Would you suggest to go on with the
project ?

Thank you,
Mirco

No, ceiling will be too low, nobody will want to live there.
Says, I, having just returned from staying at a house with 10 foot
ceilings.
Sadly, my house only has 8 foot ceilings, and it seems slightly
oppressive to me now.
I'm a shade under 6 feet tall.
At 225cm, you'd be walking into light fittings.
Simon.
So use uplighters on the walls.

"YAPH" wrote in message
...

One to switch the UFH pump on when the flow from the boiler is hot
enough to be worthwhile, another as an overheat to cut out the pump if the
flow temperature is too high.

This is of course for a set-up where the UFH is not being run as a
separate zone. Yes I know UFH takes longer to warm up so it should be a
separate zone with its own time & temp controls: this is the budget
system. If it is a separate zone then you just have the overheat stat,
wired to close the zone valve.

Ah!! you mean pipe stats, not cylinder stats. The overheat is a backup in
case the TMV fails. It still needs a room stat in case the room overheats.
It needs a non-returnvalve in front of the pump to trpevent any circuoation
frommthe systems primary pump. So, three stat in all, a TMV, non-return
valve and a pump. .and a coil of plastic pipe and some fittings. I would
say more than £100.

Best, is a heat bank using giving cheap and effective UFH using a dual
temperature boiler, like the Broag, Keston and others (avoid Keston though).
With dual temperature boilers with internal weather compensation, using a
boiler controlled 3-way diverter valve, they can reheat the DHW store top
section ASAP under full boiler heat, when heated the valve closes and it
heats the lower CH section under low temperature weather compensation
control - duel temperature boiler output. The rads or UFH pumps, pump this
water, which is the right temperature to the heating loop(s) (zones). Using
rads a Smart pump with TRVs all around can be used and no central room stat
screwing up the CH air temperature control. Then no UFH TMVs as the water
in store is the correct temperature set by the boilers integral weather
compensator. Of couse have a high limir pipe stats on the UFH loop(s).

"Simon" wrote in message
...
On 11 June, 15:17, Mirco Simoni wrote:
Hi,
I am thinking to refurbish a first floor flat with screed floors and
install water underfloor heating. I know that I have to raise floors
around 10 cm but the height between floor and ceiling is just 235 cm.
Has anyone had the same problem ? Would you suggest to go on with the
project ?

Thank you,
Mirco

No, ceiling will be too low, nobody will want to live there.
Says, I, having just returned from staying at a house with 10 foot
ceilings.
Sadly, my house only has 8 foot ceilings, and it seems slightly
oppressive to me now.
I'm a shade under 6 feet tall.
At 225cm, you'd be walking into light fittings.
Simon.

With low ceilings wall lights have to be used to five the impression of
height. Also a smooth very white ceiling.

Tommy coughed up some electrons that declared:

DEFINETLY NOT

DONT FORGET THAT DOORS WILL ALSO BE 10cm SMALLER.

Arrgh my ears!

Don't shout, mate...

Mirco Simoni coughed up some electrons that declared:

Hi,
I am thinking to refurbish a first floor flat with screed floors and
install water underfloor heating. I know that I have to raise floors
around 10 cm but the height between floor and ceiling is just 235 cm.
Has anyone had the same problem ? Would you suggest to go on with the
project ?

Thank you,
Mirco

My rooms are 2.47m floor screed to ceiling.

I am installing a layer of insulation (Marmox) leaving the finished floor
about 35-40mm higher than the screed level, so about 20-30mm higher than
previous floor finishes.

This is right at the limit of my door frames, having nailed a batten across
the door to simulate the new opening height. Any lower and it felt
claustrophobic.

Don't forget that people bounce as they walk, so standing head height
clearance is not a good indicator alone.

Now, I don't know what you plan to do with your doors, but I think 10cm off
a 2.35m height is going to make the ceilings horrible.

I presume you are looking at 40mm insulation and 60mm screed or variations.

Some variant solutions:

1) You can run sand/cement screed down to 10mm thick if you use an SBR
modified mix. I've done this - my only problem was getting it tamped level
(had to finish with some self leveller) - but my rooms were weird shapes
making the use of several tamping bars necessary and the errors occurred
generall where the walls changed direction.

2) You can get UFH (wet) panels in polystyrene which can be glued to a
subfloor (bad from heat loss POV) or glued to marmox (better) which itself
can be glued to the subfloor if that's reasonably flat.

www.floorheater.co.uk and google this group for my previous assessment of
it.

That setup is not as rigid, requiring larger format tiles, but allegedly
will also take a floating wood floor.

Cheers,

Tim

On Sat, 13 Jun 2009 10:53:11 +0100, Doctor Drivel wrote:

"YAPH" wrote in message
...

One to switch the UFH pump on when the flow from the boiler is hot
enough to be worthwhile, another as an overheat to cut out the pump if the
flow temperature is too high.

This is of course for a set-up where the UFH is not being run as a
separate zone. Yes I know UFH takes longer to warm up so it should be a
separate zone with its own time & temp controls: this is the budget
system. If it is a separate zone then you just have the overheat stat,
wired to close the zone valve.

Ah!! you mean pipe stats, not cylinder stats.

Sorry, yes. Though many cyl stats can be used as pipe stats also, and
that's what I've been using. Really need a bit of pipelag with an
appropriate cutout to ensure the stat is really sensing the pipe temp and
not ambient.

The overheat is a backup
in case the TMV fails.

Wot I said :-)

It still needs a room stat in case the room
overheats.

If you're not using the UFH as a separate zone then you'd want a room
stat, in the same way you'd want a TRV on a rad.

It needs a non-returnvalve in front of the pump to trpevent
any circuoation frommthe systems primary pump.

How would you fit this valve to allow circulation from the UFH pump but
prevent circulation caused by the system pump?

Of course if the UFH is a separate zone its 2-port zone valve carries
out this function.

So, three stat in all, a
TMV, non-return valve and a pump. .and a coil of plastic pipe and some
fittings. I would say more than £100.

I wasn't including the pipe in the price since you'd need this whether
you were rolling your own UFH mixer or buying a £300+ proprietary
mixer/manifold assembly.

Best, is a heat bank using giving cheap and effective UFH using a dual
temperature boiler, like the Broag, Keston and others (avoid Keston
though). With dual temperature boilers with internal weather
compensation, using a boiler controlled 3-way diverter valve, they can
reheat the DHW store top section ASAP under full boiler heat, when
heated the valve closes and it heats the lower CH section under low
temperature weather compensation control - duel temperature boiler
output. The rads or UFH pumps, pump this water, which is the right
temperature to the heating loop(s) (zones). Using rads a Smart pump
with TRVs all around can be used and no central room stat screwing up
the CH air temperature control. Then no UFH TMVs as the water in store
is the correct temperature set by the boilers integral weather
compensator. Of couse have a high limir pipe stats on the UFH loop(s).

And that would be less than £100?


--
John Stumbles -- http://yaph.co.uk

Pessimists are never disappointed

"Tim S" wrote in message
...
Mirco Simoni coughed up some electrons that declared:

Hi,
I am thinking to refurbish a first floor flat with screed floors and
install water underfloor heating. I know that I have to raise floors
around 10 cm but the height between floor and ceiling is just 235 cm.
Has anyone had the same problem ? Would you suggest to go on with the
project ?

Thank you,
Mirco

My rooms are 2.47m floor screed to ceiling.

Thanks Tim for spoiling my day

I have measured the heights of my ceilings. 2.32m upstairs on every ceiling.
But downstairs they are 2.30m for the rooms at the front of the house and
2.38m for the rooms at back of the house. A quick check with two neighbours
show they that have identical ceiling heights to my house.

Adam

On Thu, 11 Jun 2009 07:17:00 -0700, Mirco Simoni wrote:

Hi,
I am thinking to refurbish a first floor flat with screed floors and
install water underfloor heating. I know that I have to raise floors
around 10 cm

why?

even without insulation underneath you're not going to lose a lot of heat
to the flat below, since that will probably have something like an air gap
and plasterboard on its side of the slab (unless you're in some Eastern
European cell, or perhaps Peckham :-)).

Look up the uk.d-i-y wiki's article on UFH and there are links to some
thin wet UFH systems. One is just 15mm thick.


--
John Stumbles -- http://yaph.co.uk

This sig intentionally left blank

YAPH coughed up some electrons that declared:


Look up the uk.d-i-y wiki's article on UFH and there are links to some
thin wet UFH systems. One is just 15mm thick.

You can get 12mm now...

"YAPH" wrote in message
...

It needs a non-returnvalve in front of the pump to trpevent
any circuoation frommthe systems primary pump.

How would you fit this valve to allow circulation from the UFH pump but
prevent circulation caused by the system pump?

With no NRV the TMV may be open and circulation into the UFH zone. It needs
a positive stop to circulation. The room stat switches the pump.

Of course if the UFH is a separate zone
its 2-port zone valve carries out this function.

Yep.

So, three stat in all, a
TMV, non-return valve and a pump. .and a coil of plastic pipe and some
fittings. I would say more than £100.

I wasn't including the pipe in the price since you'd need this whether
you were rolling your own UFH mixer or buying a £300+ proprietary
mixer/manifold assembly.

Best, is a heat bank using giving cheap and effective UFH using a dual
temperature boiler, like the Broag, Keston and others (avoid Keston
though). With dual temperature boilers with internal weather
compensation, using a boiler controlled 3-way diverter valve, they can
reheat the DHW store top section ASAP under full boiler heat, when
heated the valve closes and it heats the lower CH section under low
temperature weather compensation control - duel temperature boiler
output. The rads or UFH pumps, pump this water, which is the right
temperature to the heating loop(s) (zones). Using rads a Smart pump
with TRVs all around can be used and no central room stat screwing up
the CH air temperature control. Then no UFH TMVs as the water in store
is the correct temperature set by the boilers integral weather
compensator. Of couse have a high limir pipe stats on the UFH loop(s).

And that would be less than £100?

No. But a "cheap to install", fully pro, efficient, cheap to run system.
Use the dual temperature boiler's controls to maximum advantage. This saves
a hell of a lot on expensive, bulky UFH control, and gives mains pressure
DHW that will not blow up.

The boiler maintains the UFH temp to the weather - set slope of compensator.
One UFH pump can be used off the store and each UFH zone uses a cheap 2 port
zone valve and room stat - simple and cheap. Or a pump for each zone from a
small manifold off the store, at the store. No TMVs on zones or whatever.
And the boiler is operating at a very low, highly efficient return temp all
the it reheats the UFH section of the store. Even when reheating DHW is will
be condensing about 80-90% of the time.

On Sat, 13 Jun 2009 22:46:24 +0100
Tim S wrote:

YAPH coughed up some electrons that declared:


Look up the uk.d-i-y wiki's article on UFH and there are links to some
thin wet UFH systems. One is just 15mm thick.

You can get 12mm now...

Where?

On Sun, 14 Jun 2009 09:39:36 +0100, Doctor Drivel wrote:

With no NRV the TMV may be open and circulation into the UFH zone. It
needs a positive stop to circulation. The room stat switches the pump.

I agree with the desirability of preventing the system pump pushing water
through the UFH even when the UFH pump is off. I just don't see how you
can arrange a NRV to prevent the first without also preventing flow
through the UFH from the UFH pump itself.

Assuming we have an arragement like this:


CH FLOW ---------
|
------ UFH
| TMV |-----( )------ UFH FLOW
------ PUMP
|
CH RETURN -------+-------------------- UFH RETURN

where do you propose putting a NRV?



--
John Stumbles -- http://yaph.co.uk

Things don't like being anthropomorphised.

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Mirco Simoni
saying something like:

Hi,
I am thinking to refurbish a first floor flat with screed floors and
install water underfloor heating. I know that I have to raise floors
around 10 cm but the height between floor and ceiling is just 235 cm.
Has anyone had the same problem ? Would you suggest to go on with the
project ?

Thank you,
Mirco

Use the alloy plate heat-spreader system and you lose no height. Under
the alloy plates is packed with fibreglass or rockwool insulation.

TheOldFellow coughed up some electrons that declared:

On Sat, 13 Jun 2009 22:46:24 +0100
Tim S wrote:

YAPH coughed up some electrons that declared:


Look up the uk.d-i-y wiki's article on UFH and there are links to some
thin wet UFH systems. One is just 15mm thick.

You can get 12mm now...

Where?

http://www.floorheater.co.uk/the_box.php

Grimly Curmudgeon coughed up some electrons that declared:


Use the alloy plate heat-spreader system and you lose no height. Under
the alloy plates is packed with fibreglass or rockwool insulation.

It's really about time someone did that sort of system based with PIR foam
(aka Celotex). The extra efficiency would be a winner.

Cheers

Tim

On Sun, 14 Jun 2009 15:15:53 +0100, Grimly Curmudgeon wrote:

Use the alloy plate heat-spreader system and you lose no height. Under
the alloy plates is packed with fibreglass or rockwool insulation.

The OP said he's got screed floors :-)

--
John Stumbles -- http://yaph.co.uk

This sig intentionally left blank

"YAPH" wrote in message
...
On Sun, 14 Jun 2009 09:39:36 +0100, Doctor Drivel wrote:

With no NRV the TMV may be open and circulation into the UFH zone. It
needs a positive stop to circulation. The room stat switches the pump.

I agree with the desirability of preventing the system pump pushing water
through the UFH even when the UFH pump is off. I just don't see how you
can arrange a NRV to prevent the first without also preventing flow
through the UFH from the UFH pump itself.

Assuming we have an arragement like this:


CH FLOW ---------
|
------ UFH
| TMV |-----( )------ UFH FLOW
------ PUMP
|
CH RETURN -------+-------------------- UFH RETURN

where do you propose putting a NRV?

The system pump can pump past the TMV and into the loop, although at reduced
pressure/flow. Ideally a positive stop is needed such as a zone valve.
Then no circulation. When using a spring loaded NRV best after the pump.
However if the system pump has a high pressure, some zones may have closed
down, it may be best to have one on the UFH return as well and the UFH pump
turned up to open both NRVs. You don't need to be a God to see that.

On Sun, 14 Jun 2009 23:36:20 +0100, Doctor Drivel wrote:

The system pump can pump past the TMV and into the loop, although at
reduced pressure/flow. Ideally a positive stop is needed such as a zone
valve. Then no circulation. When using a spring loaded NRV best after
the pump. However if the system pump has a high pressure, some zones may
have closed down, it may be best to have one on the UFH return as well
and the UFH pump turned up to open both NRVs. You don't need to be a
God to see that.

So basically using NRVs to add resistance to the UFH loop to help prevent
flow driven by the system pump? I think you could acheive the same effect
by using your ordinary balancing valves to increase the UFH loop
resistance.

But basically a non-zoned UFH loop is a bit of a kludge (as is much of
conventional CH practice, to put it in context). Zoned with a
motorised valve is preferable.



--
John Stumbles -- http://yaph.co.uk

I can't stand intolerance

"YAPH" wrote in message
...
On Sun, 14 Jun 2009 23:36:20 +0100, Doctor Drivel wrote:

The system pump can pump past the TMV and into the loop, although at
reduced pressure/flow. Ideally a positive stop is needed such as a zone
valve. Then no circulation. When using a spring loaded NRV best after
the pump. However if the system pump has a high pressure, some zones may
have closed down, it may be best to have one on the UFH return as well
and the UFH pump turned up to open both NRVs. You don't need to be a
God to see that.

So basically using NRVs to add resistance to the UFH loop to help prevent
flow driven by the system pump? I think you could acheive the same effect
by using your ordinary balancing valves to increase the UFH loop
resistance.

You will still need a NRV after the pump and balance it down at the return
end. Without the NRV heat will work its way into the UFH loop by force
(pump) or convection.

But basically a non-zoned UFH loop is a bit of a kludge (as is much of
conventional CH practice, to put it in context). Zoned with a
motorised valve is preferable.

Yep, a spur of the rad circuit is a kludge, as they operate at different
temperatures, and operate very differently to each other. In a well
insulated house, as say in a bedroom, it can work very well. It needs a
quicker heat up than in a screed. Having it in soft copper at rad
temperature and not touching the wooden floor above with masses of rockwool
beneath (acts as sound insulation as well) with cheap cooking foil over the
rockwool to reflect upwards (available cheap in commercial rolls) with
thermostat control can do it. Of course no carpet on the floor as in all
UFH.

You get sound insulation and no rads - so probably well worth it.

Yep most CH system are a kludge as they are just cheap, designed by rule of
thumb, retrofit systems.

On Mon, 15 Jun 2009 13:22:31 +0100, Doctor Drivel wrote:

Yep, a spur of the rad circuit is a kludge, as they operate at different
temperatures, and operate very differently to each other.

Well that's even more of a kludge. I did it once with a very small area
of UFH in the return of the radiator in a shower room. The area was so
small it wasn't worth even bothering with a pump and TMV (it was as much
to warm the tiled floor as to actually heat the room).

But I meant that a pump+TMV off the main heating loop, but not zoned, is a
bit of a kludge.

--
John Stumbles -- http://yaph.co.uk

87.5% of statistics are made up

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember YAPH saying
something like:

On Sun, 14 Jun 2009 15:15:53 +0100, Grimly Curmudgeon wrote:

Use the alloy plate heat-spreader system and you lose no height. Under
the alloy plates is packed with fibreglass or rockwool insulation.

The OP said he's got screed floors :-)

From the OP: "I am thinking to refurbish a first floor flat with screed
floors and install water underfloor heating."

Now, I took that to mean he's putting in screed floors in order to
install UFH.
Disambiguation needed, to quote a horrible phrase beloved of wikipedia.

On Mon, 15 Jun 2009 13:54:42 +0100, Grimly Curmudgeon wrote:

From the OP: "I am thinking to refurbish a first floor flat with screed
floors and install water underfloor heating."

Now, I took that to mean he's putting in screed floors in order to
install UFH.
Disambiguation needed, to quote a horrible phrase beloved of wikipedia.

Fairy Nuff, though if the OP's thinking of installing screed floors in a
first floor flat that doesn't already have them he needs more than
disambiguation ;-)


--
John Stumbles -- http://yaph.co.uk

The clairvoyants' meeting has been cancelled due to unforseen circumstances.

On Wed, 17 Jun 2009 13:08:30 +0100, Doctor Drivel wrote:

If the floor is wood and suspended and the UFH circuit is spur off the
rad circuit, I would use 12mm soft copper clipped to the side of the
joists and running through the joists in 22mm holes, so the copper does
not touch any wood. The UFH circuit then runs at rad system
temperatures and heats the space between the floor boards and the
insulation beneath.

I did something like that in my kitchen, years ago. Rockwool suspended on
netting slung between the joists, 15mm polybutylene run up and down the
gaps between the joists, suspended close to the floor surface, plywood and
ceramic tiles on top. All connected into the regular CH via a TRV under
the floor set to open when ambient temp under the floor falls below
about 18C, IIRC. It generally keeps the room nicely warm and pleasant to
walk on, though a bit patchy - some hot and some cool patches.



--
John Stumbles -- http://yaph.co.uk

The astronomer married a star

"YAPH" wrote in message
...

I did something like that in my kitchen, years ago. Rockwool suspended on
netting slung between the joists, 15mm polybutylene run up and down the
gaps between the joists, suspended close to the floor surface, plywood and
ceramic tiles on top. All connected into the regular CH via a TRV under
the floor set to open when ambient temp under the floor falls below
about 18C, IIRC. It generally keeps the room nicely warm and pleasant to
walk on, though a bit patchy - some hot and some cool patches.

I assume the TRV had a remote temperature sensor. It should work well
enough, as the water/heat will be restitcted through the UFH loop when
approach setpoint. As I mentioned, Danfoss have dedicated mechanical UFH
valves for the task.