What BTU for a radiator in this room ( in dispute with builder)

[Footgoose]

We bought a new build last year . Bedroom 1 is downstairs , has 3 outside walls and no room on top. It’s always cold . We keep the radiator switched on full to ensure the room does not become damp even though it isn’t in use full time ( daughter at Uni ) . The builders are refusing to admit there is an issue and say the radiator is actually more powerful than required .
The room is always 4 to 5 degrees cooler than the rest of the house . I have taken photographs of a thermometer in the room and main house thermostat as proof but the builders are not responding . So please , if you know about BTUs and radiators please could you tell me what size / BTU rate of radiator should be in this room.
bedoom ( ground floor , room “sticks out “ from front of house .
3 outside walls
concrete floor
no room above . Tiled roof above .
I’ve no idea of thickness of roof insulation but it is insulated and walls are insulated.
window - 2.113cm squared
height of room 1.87m
width of room 3.5m
length of room. 4.55m

i have put these measurements in to an online BTU calculator and it come out as requiring 4488 to 4702 BTUs.

The current rad measures 90mm by 60mm and rates 2500 BTUs which according to the builders is bigger than the regulations require.

with the heating on full until the thermostat cuts out at 20 degrees in the hallway, this bedroom
only reaches 16.2 degrees max.

we didn’t have the central heating on last night as the wood burner had warmed the downstairs up well enough so when I checked the room this morning it was 11 degrees ( rest of house had maintained heat at 18.5 degrees).

Not remotely an expert but I've been looking at BTUs having replaced a couple of radiators in my house recently. I think you're right in what you say.

The calculators I've used suggest around 4000-5000 BTUs for that room. There may be other factors that would influence that but a 2500BTU rad seems far too weedy. Also "minimum required by regulations" is not necessarily what's most suitable or ideal.

I think the easiest way of achieving the BTU output you want would be replacing the existing rad - which I assume is single panel if it's only 2500BTU - with a double panel rad of similar or identical size. I don't know why a developer would even query that to be honest. Assuming they're standard radiators (and also assuming your boiler is capable of delivering the additional BTUs required), it would be about £80 for the rad plus maybe an hour of a tradesperson's time.

There are other things which might need tweaking such as balancing the rads throughout the house so the one in the bedroom always gets hot enough. Also, looking at whether the thermostat is in the ideal location in the house. But first and foremost you want that more powerful rad in there.

I would be concerned they omitted insulation somewhere as much/if not more than the BTUs. 11 degrees is a real achievement for a new build.

I had this problem. Room similar size but probably better insulated.

I think 2500 is a bit low. That is a 90cm x 60cm, but a quick look on screwfix implies that would be a single radiator rather than a double.

A double would not surprisingly double the BTU.

So are you sure they didn't fit a single instead when they meant a double ?

If it is plastic pipe it should be pretty simple if they have fitted a single to replace with a double ?

Hi . Thank you for replies . The builders have been back to balance the rads a couple of times . No avail . We could easily replace the rad with a double but I’m not sure that would solve the problem . The rad is only a part of the problem . I suspect the room is losing heat for some reason . Over ventilated ? Poorly insulated . I’m trying to gather as much info as I can.

we are a small development of same style new builds . We all have the same issue with bed room 1 . Once the builders accept there is an issue with one of us they are going to have to correct the problem with all of us . I think that is why they are being resistant . One property has already upgraded the rad at their own expense and say it has made little difference.

@Footgoose one of the best things you can do is to rent a hand held thermal camera, we bought one from Amazon for about £350 but you can rent them. It showed us that we had a whole strip in our loft of missing insulation which was a surprise, it will help you see if there are any colder spots in the room like a crappily installed window or missing insulation in the walls.

Building regs for insulation etc is the bare minimum. Ask them specifically how much they put in. Clearly there is an issue and it is probably two fold, the rad and you are leaking heat somehow.

Also what floor covering do you have? Carpet?

I have recently bought thermal imaging. It was about £200 for android.

It's great at showing hot spots and cold areas and has helped me sort my loft insulation and learn more about how to reduce heat leak in my house.

A bit expensive though just for a one off.

What you could do is get an IR thermometer and take the temperature of the walls at various points. That should give you an idea of whether or not there are any cold spots and whether the roof is colder than the walls. These are cheaper.

My guess is the outer walls will all be of the same construction, so will probably all be the same. The roof will be different.

It is surprising if it is a new house that it is cold.

I still believe your radiator is undersized for that room. With it being a new build is it gas boiler or heat pump ?

One of my houses had zero insulation fitted above one bedroom. It was really cold.

Yy to the thermal camera.

Once your builders have sorted this as much as they can, if you are not satisfied, look into thin polystyrene wall liner - comes in a roll 0.25 thick and can go under wallpaper. You shouldn't need it in a new build but it's a good fix.

@SudenAlia

Snap !

I found that they hadn't rolled the insulation properly to the edge (you have to leave a bit of a gap though for insulation) in a lot of places. Whoever had boarded the loft removed a lot of the insulation and piled it up under the eves. The thermal imaging enabled me to fix it.

This is a photo of the problem . The heating will kick off shortly and leave this room cold . I will look in to thermal imaging , thank you for the information. I hadn’t realised we take investigating and monitoring the heat loss into our own hands as easily as this .

You need thermostats on each individual radiator for a start.
More insulation above the room in the roof space
Thermal curtains.
You may well be able to get thermal wallpaper, I'm pretty sure my parents have something like that in part of their house.

Is the radiator fully hot all over?

Top, bottom, middle and sides?

The incoming pipe xhould be too hot to hold, and the rest of the rad should be too hot to hold for long.

Great advice, was about to suggest the same thing. Choose a cold evening, turn off the light, check the walls, ceiling/roof, floor. And check again from outside. Its a dreadful design - which you can't do a lot about now, but bad construction may well be compounding your difficulties.

Something else that might help would be to fit thermostatic radiator valves throughout the house then put the thermostat in the offending room (if it can be moved of course, not all can) Not sure if the boiler would appreciate heating just one room. But the situation might be being made worse by the rest of the house coming up to temperature quite quickly, so the heating then goes off. If you moved teh thermostat, the radiators would shut off as the rest of the house reached the radiator set temp, but the boiler would know that last bedroom was still cold, and carry on?

heh @Catmummyof2 snap!

We have this with one of our bedrooms, we have a dehumidifier running constantly in there now as it feels colder with the damp winter air.

Yes, we have individual smart valves that integrate with our Hive and are easily retrofitted.

As it's a new build, with a roof abovd:

First look in the roof space, because this is potentially the biggest heat loss. The insulation should be about ten inches thick, in top layers, the top one running crossways. This is actually more than enough for UK, providing that it is properly laid. It must completely cover the ceiling* If somebody has made holes in the ceiling, for downlighters or pipes to poke through, and warm air to rise out of, they should be sealed and insulated over. You can get fireproof hoods to go over downlights. It is quite common for people working in lofts to pull the insulation out of the way and fail to put it back. The insulation is so thick that the timbers will be buried and you cannot safely walk on them. If you have to work in a loft, buy two pieces of 18mm ply about 900mm x 600mm. They will not be too heavy to carry, or too big to go through the loft hatch. You can rest them on the timbers to stand on. Having two means you can stand or kneel on one while placing the other.

*However it must not be pushed tightly into the eaves and block ventilation, this will encourage damp. It is correct for lofts to be cold and draughty, they are outside the heated envelope of the house.

As it is a new build I would hope you have Thermostatic Radiator Valves throughout; except in the room where you have your wall thermostat. Have you?

Who balanced the radiators, and how long did they take? Do you have reason to believe they were competent?

Walk round the room with a smoking joss stick. It will show up any draughts.

@Footgoose the camera is great and helps to identify exactly what is cold. It might be worth looking at this as a multi point attack. Get the camera (we have lent ours out to friends) to pin point if the outside wall of this room is different than any of the other outside walls temperature wise. Look at upgrading the radiator and like @Mumaway look at the individual radiator smart valves.

As it stands the heating will cut out when that thermostat reaches 20 degrees but other rooms might be colder and so need heat for longer. This is why thermostats that can be moved are better than fixed to the wall. Just because one room gets to 20 doesn't mean the rest have. We moved ours around until we found a spot that meant we weren't roasting hot in the lounge.

It is completely shit when you have bought a new build and experience these issues. There are lots of videos on youtube on how to use the thermal camera and also on smart valves. Youtube is a great resource.

P.s.

Loft insulation is 250 to 300mm thick.

Cavity wall insulation is 50 to 70mm thick.

The polystyrene wallpaper is about 2mm thick. It might feel warm when you put your warm hand on it, because it reflects your own heat back at you. But its value as house insulation is negligible.

Was the building sold to you with a building warranty? If it was, I'd contact the warrantor for advice.

A couple of basic things to add.

Pigletjohn is right to question who balanced your radiators. It’s a bit of an art and apparently a lot of plumbers really don’t know how to do it very well.

A room with three external walls will always be colder due to exposure.

Is your thermostat on an external wall, by any chance? Some ours are, it is bloody daft and wreaks havoc with temperature fluctuations, especially when the wind picks up.

Finally, it’s not over a garage is it? Because that could be a not enough floor insulation for the cold space underneath issue.

@PigletJohn , thanks for taking the time with such comprehensive advice The builders have been back to balance the rads. The loft about the bedroom has no hatch so we can see the insulation. No spot lights . I’ll get a thermal imaging camera / and do the joss stick test .
thank you .

All excellent advice above, however I've gotten distracted - is the ceiling height really only 1.87m?!

I was under the impression that minimum ceiling height was 2m so I'd be questioning that with your builder also!