*HELP* UFH overlay system with Insulation or Screed or (Insert answer)???

[Jeremy Harris]

23 minutes ago, scottishjohn said:

I have no calculations, just the one that matters --how much energy i have to pay for  and that said 20%less with suspended floor retro fit UFH  than with rads 

maybe that is the way  then air gap and insulated suspended floor with thin screed if looking for best economy  in heating costs ?

or should it be same 300eps then slab ,then 100mm eps and ufh then choice of floor ?

what do your numbers say to that ?

 

 

First off, they are not "my numbers" at all, they are just bog standard heat loss calculations that use well-proven laws of physics.

 

The difference between an insulated suspended floor and an insulated ground bearing slab is that the worst case heat loss for the suspended floor will always be higher, irrespective of the form of heating, because the worst case temperature differential will always be higher.  A suspended floor will have a temperature on the underside that mirrors the outside air temperature, as it will be ventilated, so cold air will flow underneath it.  A ground bearing slab has a near-constant temperature all year round of about 8°C underneath it, so is warmer underneath in very cold weather and cooler underneath in very warm weather.  This difference effects the heat loss rate for each floor construction method.

 

It's pretty easy to calculate the heat loss rate for any floor type, build up and temperature differential, and the bottom line is that if this heat loss rate is increased, for any reason, then that will increase the heating cost for the same heating requirement.  Of course, if other work done decreases the heating requirement that may outweigh the additional heat loss from fitting UFH, but that doesn't change the basic fact that heating the floor always results in higher losses than heating the room.

 

 

[PeterW]

3 minutes ago, Ian said:

Re the efficiency discussion comparing UFH to radiators, I’ve found with our UFH that, for the same levels of comfort, we can set the thermostat to a lower temperature than would be the case with a conventional radiator system

 

Its because it heats your feet not your head first..! It is an odd one, if you look at the thermal gradient in a room for one with rads vs UFH, you get a hot top down gradient. With UFH, it rises but as the delta is smaller between air and surface, the gradient is lower.

 

7 minutes ago, scottishjohn said:

maybe we should be building with strip foundations then subwalls and fill inside them with 300-400m insulation and fully floating floor on top of it with UFH built in ?

no big heat store in floor then --so only heat it when you need it - temp will change very quick then  and low heat losses?

 

The controls needed to do this are incredibly complex as the hysteresis needed along with the PID algorithm would need to be able to control the temperature of the flow as well as the flow rate. In addition, the flow paths in a room are not perfectly linear you may get variations in overall room temperature for the same set point depending on thermostat location

3 minutes ago, Onoff said:

In effect what many have done here. Biggest problem seems to be the places can be TOO WARM and require cooling.

 

 

Got that the wrong way round - a lot have a big heavy slab contained in an EPS shell. What was being proposed was the other way round.

[ProDave]

The "lower room temperature" with UFH stems from the fact that with radiators, in a room with a poorly insulated floor, the temperature at floor level will be lower. So when sat down, your feet will be in cool air so you will feel cold and turn the thermostat up.

 

UFH gives a much more even temperature including being warmer at floor level so you won't feel as cold so can turn the thermostat down a bit.

 

Whether that reduction in temperature (which will lower roof and wall heat losses) is enough to compensate for the higher heat loss through the floor depends on many things, it some cases it might, in others it might not.  But if the floor insulation is marginal to poor, I suspect the running cost of UFH will be higher.

 

 

[scottishjohn]

2 minutes ago, PeterW said:

The controls needed to do this are incredibly complex as the hysteresis needed along with the PID algorithm would need to be able to control the temperature of the flow as well as the flow rate. In addition, the flow paths in a room are not perfectly linear you may get variations in overall room temperature for the same set point depending on thermostat location

I agree with you which was why i used a thermal store with my system to stop "hunting on lpg boiler +I had solar thermal input to this as well and due to house type each room has its own stat+programmer  and zone valve 

the down side is the no one keeps all the doors shut to each room .LOL

so  slightly pointless -- so now its ended as basically an upstairs and downstairs zone 

 that works fine -- and i can see with small heat store in floor you need to store it in a large tank ,which is where my idea of combined solar thermal +PV and tall  large store comes in 

that is easy to insulate to death if you want to in the service area 

[Dreadnaught]

31 minutes ago, Ian said:

Re the efficiency discussion comparing UFH to radiators, I’ve found with our UFH that, for the same levels of comfort, we can set the thermostat to a lower temperature than would be the case with a conventional radiator system

 

I suspect (without evidence) that UFH provides a more even level of infra-red radiation within the room, which may account for this. The IR radiation would give a pleasing sense of warmth to the skin. Sensory perception.

[scottishjohn]

deifnitley  Ifound this with my garage workshop -which is 25mx 24m

we used to have blown air heating then changed to infrared gas tube heaters

this heated the ramps the floor the mechnaics toolboxs etc --anything and everything ,which then radiated to the air .what was very noticeable was that when the big doors were opened for a car to come in the temp recovered much quickerwhen door was shut  than when when blown air heating ,as all that went out of the door when it was opened 

 

I think it is the same with UFH --it heats all the furniture etc at a low level ,so opening doors does  not drop temp same as with rads 

[Onoff]

44 minutes ago, PeterW said:

Got that the wrong way round - a lot have a big heavy slab contained in an EPS shell. What was being proposed was the other way round.

 

?

[Jeremy Harris]

 

 

21 minutes ago, scottishjohn said:

I think it is the same with UFH --it heats all the furniture etc at a low level ,so opening doors does  not drop temp same as with rads 

 

Just to be clear about all this stuff about radiated heat etc.  Our UFH operates with an absolute maximum floor surface temperature of 23.9°, when the room temperature is 21°C and the outside air temperature is -10°C.

 

99% of the time the floor temperature never exceeds about 22°C

 

I challenge anyone to feel any difference at all between the floor at 22°C and the room at 21°C.  I can measure it, but certainly can't feel it.  I doubt that anyone could feel any noticeable radiant heating effect, either.  Not even my thermal imaging camera shows anything up.

[Dreadnaught]

11 minutes ago, JSHarris said:

Just to be clear about all this stuff about radiated heat etc.  Our UFH operates with an absolute maximum floor surface temperature of 23.9°, when the room temperature is 21°C and the outside air temperature is -10°C.

 

99% of the time the floor temperature never exceeds about 22°C

 

I challenge anyone to feel any difference at all between the floor at 22°C and the room at 21°C.  I can measure it, but certainly can't feel it.  I doubt that anyone could feel any noticeable radiant heating effect, either.  Not even my thermal imaging camera shows anything up.

 

I think that's a good challenge. I therefore suspect that the beneficial feeling from IR radiation on the skin derives from having uniform and stable internal temperature alone, and the source of the space heating (UFH in this case) is only minimally relevant. Once the temperature is maintained for a long period, all surfaces and objects within the space become noticeable IR emitters.

 

The stable internal temperature, of course, comes from the usual passive-house-style principles: high levels of continuous thermal insulation for the envelope, long decrement delay, air tightness, heat recovery, etc. In other words, a fabric-first approach.

Edited July 3, 2019 by Dreadnaught

[Jeremy Harris]

2 minutes ago, Dreadnaught said:

 

I think that's a good challenge. I therefore suspect that the beneficial feeling from IR radiation on the skin derives from having uniform and stable internal temperature alone, and the source of the space heating (UFH in this case) is only minimally relevant. Once the temperature is maintained for a long period, all surfaces and objects within the space become noticeable IR emitters.

 

The stable internal temperature, of course, comes from the usual passive-house-style principles: high levels of continuous thermal insulation for the envelope, long decrement delay, air tightness, heat recovery, etc. In other words, fabric-first approach.

 

I suspect that much of the perceived difference is just from the way we tend to sense body heat loss.  One of the first things I noticed with the 3G in the new house was that there is no feeling of it being a bit cooler when standing in front of the glazing on a very cold day.  The inner pane of glass is very close to room temperature, and this fools us into thinking that the part of the room in front of the glazing is warmer than would be the case if standing in front of less efficient glazing. 

 

This isn't wholly explained by the difference in U value, either, I think much of the perceived difference comes from having two low e coated panes of glass in 3G, versus just one in 2G.  The low e coating only reduces the radiated heat loss out through the glass, by reflecting it back inwards, and I think we can sense that reduction in radiated body heat loss.

 

 

[scottishjohn]

13 minutes ago, JSHarris said:

I suspect that much of the perceived difference is just from the way we tend to sense body heat loss.  One of the first things I noticed with the 3G in the new house was that there is no feeling of it being a bit cooler when standing in front of the glazing on a very cold day.  The inner pane of glass is very close to room temperature, and this fools us into thinking that the part of the room in front of the glazing is warmer than would be the case if standing in front of less efficient glazing. 

what you are seeing there is exactly what I was eluding too in the difference between rads +ufh that I noticed 

with rads I never felt the cold radiation from the windows ,but very noticeable once I swopped to UFH

 

[Jeremy Harris]

5 minutes ago, scottishjohn said:

what you are seeing there is exactly what I was eluding too in the difference between rads +ufh that I noticed 

with rads I never felt the cold radiation from the windows ,but very noticeable once I swopped to UFH

 

 

 

That's most probably because the traditional place to put radiators was underneath windows, so the area in front of windows would often feel fairly warm compared to elsewhere.  There's no "cold radiation" from windows, as "cold" doesn't flow anywhere, by any means.  All we have is heat flow, and that can be varied by the effectiveness of insulation.

[scottishjohn]

32 minutes ago, JSHarris said:

 

 

That's most probably because the traditional place to put radiators was underneath windows, so the area in front of windows would often feel fairly warm compared to elsewhere.  There's no "cold radiation" from windows, as "cold" doesn't flow anywhere, by any means.  All we have is heat flow, and that can be varied by the effectiveness of insulation.

 yes agreed, sort of,but not in my house the one big double rad was on the back wall and window was not on that wall.

so you do feel radiation of a lower temp ,eg cold ,from that area .

anything above absolute zero is heat 

Edited July 3, 2019 by scottishjohn

[Ferdinand]

18 hours ago, Da-Dad said:

Hi folks

 

Just your friendly neighbourhood UFH newbie here - I'm hoping you can help me out with some advice...I've spent HOURS researching and still cant come to a decision *my mind is gonna blow!!!*

 

We really would like Wet UFH in our Bungalow that is undergoing renovation (has a combi boiler radiator system), the key concern is keeping the profile as low as possible (only 78 inch height on the doors openings) and ensuring the system is still efficient and affordable.

 

The floor of the house is concrete, think there is no insulation in there since it was built like 50+ years ago.

 

 

I did a "layering up reno" on a 1970 bungalow in 2017 ("Little Brown Bungalow"), which has many similarities and a couple of differences (mainly suspended floor, and I did not use overlay ufh *this* time - I will do so next time as I have enough answers now to give me confidence), that we chatted about on here. But let me make like Eric Morecambe and answer all your questions, but not necessarily in the right order..

 

For ufh imo there are two things: the overall output is modest, and you lose a lot of heat downwards. For it to be effective and affordable, you need a house with decent quality fabric, and that must specifically include the floor. If you have not got those, then you either need to mitigate, not bother, or accept a potentially cold house and / or high bills.

 

The target I adopted was current new building regs standard for the fabric, and accepting that I would need to compromise so would still hopefully be better than renovation regs standard. My compromise was that I accepted the existing walls with a poor u-value of 0.55 (=brick with cavity insulation), but did better on the roof, floor and windows.`

 

1 - You need to consider how far you can "profile up". I discovered that doors with trimming margins of more than 65mm are hard to find without going custom, and I still have a 1m high stack of 50mm celotex sheets to remind me. You need to work to 50-55mm in your spec, not 65mm, unless you have doors I did not find or have solid wood originals that can be cut back more. In addition to your extra floor, you need an opening / ventilation gap, and also a trimming contingency for eg if your carpet is fluffier then expected.

 

If not you could be up a gum tree without a kangaroo, with your doors disintegrating because you had to cut off too much. My doors came from Todd Doors; other suppliers are mentioned on the forum. I had to trim an extra 5mm of 2 of mine, due to higher quality underlay and carpet than planned.

 

There are ways to make floor surfaces thinner, but you may need eg something over your ufh system before you put a carpet on it. Will leave that for another post. 

 

2 - Will you personally fit your lower ceilings etc? My doorways ended up as 1.92m, reduced from 1.98, but I am only 1.75m so it is OK. If you happen to be 1.93m, then you will be doing in a policeman's bob everytime you go through a door, which is not OK. Similarly ceilings - mine came down to 8ft exactly, but eg 7'6" would only work in a cottage.

 

3 - IMO 30mm of Celotex is not enough. You want something more like 75-100mm or equivalent. But there are alternatives. These are all dependant on having decent insulation everywhere else.

 

a - Use a product like 25-30mm of aerogel, say Spacetherm or ThermaSlim. But that will cost at least  £75 per sqm. How much do you like ufh? 

b - Raise the height of your door frames by one course of bricks if your ceiling heights can take it, and have enough insulation.

c - Use "perimeter insulation" - installed as a 18" to 2ft deep ring outside your walls. That will cause the heat to stay under your house, and act like more insulation as the ground is warmer 2" down.

d - Accept that the ufh is background and that you will lose 30-40% of your heat downwards, and fit eg a log burner for winter.

e - Fit rads.

 

(I would do these in order bacde or bcade depending on the project.)

 

4 - It sounds as though you should take a look at the other thermal elements - wall, floor, windows.

 

5 - Whatever you do, thorough attention to airtightness detail (and appropriate ventilation) is important. Also consider what will be done when you have to move on from Gas.

 

6 - Recommend that you thermally model it using the @JSHarris spreadsheet.

 

In summary - yes you can make it work, but if your fabric is going to be largely unimproved then perhaps go for oversized rads. But it is worth doing the fabric properly if you plan to stay. My opinion is aim for an EPC of C (=75-80) or better.

 

The two threads that might be useful, which include before and after photos on the LBB, and also my actual floor buildup, and the one I would use for ufh, are:

 

 

 

Ferdinand

Edited July 3, 2019 by Ferdinand

[Pocster]

Guys !

 

Remember if you are struggling to get enough depth in PIR there is always vacuum insulation - but at a high cost of course ! . Just a thought 

[Onoff]

29 minutes ago, pocster said:

Guys !

 

Remember if you are struggling to get enough depth in PIR there is always vacuum insulation - but at a super high cost mere mortals can't afford of course ! Just a thought 

 

So you're going for vacuum insulation everywhere then? ?

[Pocster]

2 minutes ago, Onoff said:

 

So you're going for vacuum insulation everywhere then? ?

Git 

[Ferdinand]

2 hours ago, pocster said:

Git 

 

Cheaper option for you, @pocster, might be to get dressed.