Help to understand UHF needs and best operation and design

[Okeb]

Hi,

 

I read the forum extensively, and see that the general suggestion is not to have many zones (if at all), however there are many here also with off the shelf designs with multiple zones and they are also happy with it.

In addition, I could not find much answer if my boiler would be good enough for an efficient system, so I am looking for some advise.

 

Bought a house recently in the middle UK.

5 bedroom, detached, ground floor and first floor, built in 2009.

 

I plan underfloor water based heating on the ground floor, but so far I only got generic system quote (without plan) from Wunda.

Currently there are radiators everywhere, and in general they heat up nicely, so don't think I have much issue with heat loss, but I do not know exactly the heat loss.

 

Floorplan is attached.

-Floor: as I know it is beam and block, the closest I could get is an old photo from one of the neighbour who dug it up for extension, it is insulated as I know. Top of the floor is concrete with some self levelling and probably damp proof layer (photos attached)

-have wooden windows, double glazed

-planned floor type: kitchen/diner/utility and toilet would be tiles, everywhere else laminate

-current boiler: Mains Eco Compact, heat only 24kW, manual know to set temperature, so cannot do weather compensation. I think it is on an S plan

-heating, hot water: un-vented hot water tank (210l), upstairs radiators on a dedicated loop with a thermostat, downstairs radiators on a dedicated loop with a thermostat, and the hot water tank has it's own valve. One motor. All are at the hot water tank, upstairs.

 

The plan is to retrofit a 20mm EPS system with 16mm pipes. EPS boards would be directly glued to the floor (kitchen, utility has tiles now, they will be removed, everywhere else we have carpet and the image attached shows what is under the carpet).

 

Have a quote for materials from Wunda around £3.6k, this includes 5 zones, with 5x thermostat and floor temperature probes for laminate.

-tiles directly on top of the boards

-laminate with an underlay directly on top of the boards

 

Does all this sounds ok? Is it ok not to screed it over (that would add considerable cost).

 

What about the zoning? Most of the time the door between kitchen and sitting room is open, as well as the door between kitchen and hallway, and most of the time the sitting room and hallway.

I would not mind have all on only one zone, or two, maybe the Lounge on a separate zone as that will be my workplace and I would enjoy 1-2 degree less heat.

If no zoning, how the system will make sure that the laminate do not go above 27 degrees C?

 

What about the boiler? Overall I think it is overkill for heating, but that's what I have. 

Is it worth to consider ASHP? Or a more modern weather compensated boiler?

 

Or just leave all as is, and use the rads and don't install UFH? My partner would enjoy warm feet though...

 

thanks for any comment!

 

 

 

 

[ProDave]

You need to be SURE of the block and beam make up.  If it is NOT well insulated then 20mm of insulation with the UFH will NOT be any good.

 

We can't form much of an opinion from the picture as the "blocks" are missing and all that is there is the beams over a presumably cold ventilated void.

 

You need to solve that one before spending any more effort on this, it might not be viable without a LOT of work.

 

You don't fit UFH for "warm feet"  the floor temperature will only be a few degrees above room temperature, so barely enough to make a floor feel "warm"  You fit it for even temperatures without the hot spots radiators inevitably give you, and not having  radiators taking up walls space and limiting your furniture placement.

[JohnMo]

For me you are wasting a load of money and effort doing UFH. Block and beam and thin insulation you will be chucking money down the toilet year on year in increased running costs.

 

28 minutes ago, ProDave said:

"warm feet"

I read an article the day about radiators and cold feet. The reason people get cold feet - the heating runs an on off strategy with high temperature radiators. Radiators don't really radiate heat they heat air via convection. The convection current is quite strong with high temperatures. The hot air goes the ceiling and cold drops to your feet. Thermostat stops the radiator the room cools, you still have cold feet the cycling repeats.

 

Solution is low temperature heating, so with radiators you can run weather compensation or load compensation. So the heating is lower temperature and more continuous.

 

Your easiest option is to get your boiler to run opentherm and move to priority domestic water, so you can get two flow temps one for DHW heating and a variable temp for heating.

 

You need to share your boiler details also.

Edited October 9 by JohnMo

[Gus Potter]

18 minutes ago, JohnMo said:

Your easiest option is to get your boiler to run opentherm and move to priority domestic water, so you can get two flow temps one for DHW heating and a variable temp for heating.

Great post John.

[JohnMo]

3 minutes ago, Gus Potter said:

Great post John.

Thanks

[Okeb]

9 minutes ago, JohnMo said:

For me you are wasting a load of money and effort doing UFH. Block and beam and thin insulation you will be chucking money down the toilet year on year in increased running costs.

 

I read an article the day about radiators and cold feet. The reason people get cold feet - the heating runs an on off strategy with high temperature radiators. Radiators don't really radiate heat they heat air via convection. The convection current is quite strong with high temperatures. The hot air goes the ceiling and cold drops to your feet. Thermostat stops the radiator the room cools, you still have cold feet the cycling repeats.

 

Solution is low temperature heating, so with radiators you can run weather compensation or load compensation. So the heating is lower temperature and more continuous.

 

Your easiest option is to get your boiler to run opentherm and move to priority domestic water, so you can get two flow temps one for DHW heating and a variable temp for heating.

 

You need to share your boiler details also.

Thanks for your advise.

 

The boiler is mentioned above. It has a manual knob to set the temperature, so don't think it can be connected to opentherm.

https://www.mainheating.co.uk/main-products/gas-boilers/main-eco-compact-heat

 

In one of the room downstairs I removed the carpet and the underlay, and checked with a thermal camera after a colder night (maybe 6-8deg), and in general the floor temperature was similar to the walls and did not see cold spots, only a small bit around the window. Room did not feel cold. That is is why I think it is "well" insulated, but I do understand that I can drain money to heat the void. 

 

[Okeb]

48 minutes ago, ProDave said:

You need to be SURE of the block and beam make up.  If it is NOT well insulated then 20mm of insulation with the UFH will NOT be any good.

 

We can't form much of an opinion from the picture as the "blocks" are missing and all that is there is the beams over a presumably cold ventilated void.

 

You need to solve that one before spending any more effort on this, it might not be viable without a LOT of work.

 

You don't fit UFH for "warm feet"  the floor temperature will only be a few degrees above room temperature, so barely enough to make a floor feel "warm"  You fit it for even temperatures without the hot spots radiators inevitably give you, and not having  radiators taking up walls space and limiting your furniture placement.

Is there a way to know construction? Do they drill and check?

 

The house ground floor is level with the ground. the only ventilation I could see to the void below the beams are the vent bricks. But I am not sure they are connected to the void below.

So if the void below the floor is not open void, then it is a on it's own insulating as a trapped air, isn't it?

[JohnMo]

1 hour ago, Okeb said:

Mains Eco Compact, heat only 24kW, manual know to set temperature

Sorry just seen this, yes pretty basic boiler. Maybe better spending your money on a better boiler.

 

3 minutes ago, Okeb said:

Is there a way to know construction? Do they drill and check

Can you estimate it's thickness?

 

Your B&B plus screed say 250 to 300mm. If it's suitably insulated it will be closer to 450 to 500mm thick.

[saveasteading]

16 years ago what was the required floor U value? I  might have an old manual, somewhere. 

I'm going to guess at the equivalent of 75mm pir. But putting none in the floor and more elsewhere was more common then.

I  agree with the warm feet principle and that 20mm of pir (twice as good as eps,  might be worthwhile. Do Wunda do a pir version?

BUT on balance you'll lose a lot of energy down to the void, so I'm thinking live with it especially if the boiler is gas. And put 300mm of fg in the loft.

[Gus Potter]

17 minutes ago, saveasteading said:

16 years ago what was the required floor U value?

In Scotland the U value for a floor in 2010 was 0.2 W/m^2K. See below for the value above the red box. This is an extract from a energy calc I was doing on a retrofit, looking at the roof, so had to dig out past regs. 

 

 

Current Scottish Standards are for individual elements on say an extension, but a good starting guide for new build.

 

 

As it's a bit baltic up in the north of the UK the English regs, I guess, at that time were using a value of maybe 0.25 W/m^2K as traditionally the English regs are slacker than the Scottish regs. 

 

Current basic Scottish regs are below. 

 

One thing to take away from this is that the Scottish Standards are more onerous than in England, have not look at NI yet in detail.

 

 

[Okeb]

15 hours ago, JohnMo said:

Your B&B plus screed say 250 to 300mm. If it's suitably insulated it will be closer to 450 to 500mm thick.

You are right, image is cropped, but on the full one I referenced to a wall socket size and the total floor thickness is around 200mm

 

15 hours ago, saveasteading said:

BUT on balance you'll lose a lot of energy down to the void, so I'm thinking live with it especially if the boiler is gas. And put 300mm of fg in the loft.

But the void is air, and air is good insulator? It is under the floor with no visible air opening, unless brick air vents provide that, what I do not know.

 

14 hours ago, Gus Potter said:

As it's a bit baltic up in the north of the UK the English regs, I guess, at that time were using a value of maybe 0.25 W/m^2K as traditionally the English regs are slacker than the Scottish regs. 

Thanks Gus, that is what I found, 0.25 W/m^2K

 

 

So a bit of calculation, if I understand it.

-100m^2 ground floor with the above U value

-lets assume when heating needed it is average 4 degrees outside, room set to 21 degrees

-Heating period of the year lets say 220 days

 

1, Radiators

Thermostat at 21deg, close to floor is around 19 deg.

Heat loss per year: 100 * 0.25 * (19-4) * 24 * 220 / 1000 = 1980 kWh

 

2, Underfloor

I assume higher heat loss because we do heat close to the floor, what is warmer as well than the room

Thermostat at 21 deg, what can be the temperature used? Maybe 30? (not directly the water temperature I assume)

Heat loss: 100 * 0.25 * (30-4) *24 *220 / 1000 = 3432 kWh

 

The difference is 1452 kWh, what is for a 8p/kWh rate on gas with efficiency of ~90% would cost £129.

 

Is this how it is calculated? So I will be worse by £129 each year, but on the contrary comfort can be better, and maybe run at lower temp so it might be slightly lower?

 

 

[saveasteading]

My main point is to check that you have floor insulation, thickness and what material: don't assume.

 

Is there somewhere you can easily check eg at a  hatch you could assess the thickness.

OR somehow get an accurate report on the neighbour's floor. That looks just uninsulated to me, but hollow blocks helping a bit.  There are ways of playing with the numbers to get building regs especially back then.  The actual number could be dreadful. It would not suit ufh.

 

Air in a large void is a very poor insulator. Ground is better.

[JohnMo]

20 minutes ago, Okeb said:

You are right, image is cropped, but on the full one I referenced to a wall socket size and the total floor thickness is around 200mm

 

But the void is air, and air is good insulator? It is under the floor with no visible air opening, unless brick air vents provide that, what I do not know.

 

Thanks Gus, that is what I found, 0.25 W/m^2K

 

 

So a bit of calculation, if I understand it.

-100m^2 ground floor with the above U value

-lets assume when heating needed it is average 4 degrees outside, room set to 21 degrees

-Heating period of the year lets say 220 days

 

2, Underfloor

I assume higher heat loss because we do heat close to the floor, what is warmer as well than the room

Thermostat at 21 deg, what can be the temperature used? Maybe 30? (not directly the water temperature I assume)

Heat loss: 100 * 0.25 * (30-4) *24 *220 / 1000 = 3432 kWh

 

The difference is 1452 kWh, what is for a 8p/kWh rate on gas with efficiency of ~90% would cost £129.

 

Is this how it is calculated? So I will be worse by £129 each year, but on the contrary comfort can be better, and maybe run at lower temp so it might be slightly lower?

 

 

Sort of 

Use the heat-loss formula:

Q=U×A×ΔT

where

U = floor U-value (W/m²·K) to the underside/cavity,

A = floor area (m²),

ΔT = temperature difference between the warm floor (mean UFH floor temperature) and the space below/crawlspace/ground (K). So you need to use your average UFH flow and return temperature.

 

Average winter temp is around 7 degs (void space temp), air is a good insulator if in a closed box, but your void will be ventilated, so not good.

 

Best case U value will be building regs, it can be worse and compensated in other areas. But we will use 0.25.

 

Flow temp likely to be mid 30s so 35 flow and 30 return so 32.5 mean.

0.25x100x(32.5-7), so 640W.

640 x 24 x 220, so about 3400kWh

At 8p that's £270. If your flow temp is higher your losses get higher. If you can flow lower well done but I doubt it. The above is based on average temp, so milder days less losses, design day losses double. So on a -3 day your downward losses alone will cost £2.30.

[saveasteading]

4 hours ago, JohnMo said:

air is a good insulator if in a closed box

Sort of. In a narrow box such as double glazed units, a tiny air gap creates a large improvement, very much more than with secondary glazing, because the air circulates.

 

In a floor void It will heat up and circulate too. There should be air bricks and they will suck the heat away too. Even if there aren't, there will be draughts.

 

22 hours ago, Okeb said:

dug it up for extension, it is insulated as I know

I can't see insulation. The blocks are about 150mm, then a slab on top, but I don't see insulation.

[Okeb]

20 hours ago, JohnMo said:

Flow temp likely to be mid 30s so 35 flow and 30 return so 32.5 mean.

0.25x100x(32.5-7), so 640W.

640 x 24 x 220, so about 3400kWh

At 8p that's £270. If your flow temp is higher your losses get higher. If you can flow lower well done but I doubt it. The above is based on average temp, so milder days less losses, design day losses double. So on a -3 day your downward losses alone will cost £2.30.

 

Good to see we got to the same calculation (3400kWh vs 3432kWh).

£270 a year yes, but with the radiator it is around £106-140 a year, so the difference is lets say £150, but better comfort I assume, so might still worth it.

 

 

15 hours ago, saveasteading said:

I can't see insulation. The blocks are about 150mm, then a slab on top, but I don't see insulation.

 

The white bits in the image are the insulation I guess, it's broken in pieces, but visible on some part of the floor closer to the wall, also closer to the bottom of the picture, pieces fall into the void also.

I upload the full image, what shows a bit more.

 

Unfortunately no access to the void, and you are right, the air bricks are likely vents for the void (as per this video: https://youtu.be/nuqlgDe33Gc?si=wfu0XLxeBOkZR0rq&t=22 )

 

Adding insulation to the floor, lets forget that it adds height, but a 100mm PIR would reduce heat loss by about £140 per year, but material cost is £1200 plus put it down, so it would take like at least 10-15 years to break even.

And the vacuum insulation panels cost is just out of question.

 

 

Will look into low temp heating with rads and consider my options, even boiler change or other improvements, but I am not fully disqualifying the UFH.

Roof already has 200mm+ insulation. 

 

[JohnMo]

22 minutes ago, Okeb said:

better comfort I assume

Better comfort compared to running radiators at 70 yes, but doing lower flow temp radiators, no should pretty similar.

 

24 minutes ago, Okeb said:

And the vacuum insulation panels cost is just out of question.

Damage risk huge, payback your grand kids may see some.