New system struggling to reach room temp 21 deg

[oldman2]

I had a new Worcester Bosch 28i combi complete system fitted last August. The company made a pigs ear of the job though I did end up with a working system in the end.
During the recent cold spell I had to have the heating on 24/7 to realise 19 deg c in my lounge area, not wishing to maybe end up with a non working system I delayed calling in the installer to explain why until the worst of the weather is over.
I dont have a problem with the rest of the house heating as we all like our bedrooms on the cold side and the trv's work well for this. Hot water supply is fine.

The lounge is 36ft x 13ft with a large window south facing, the dining area has patio doors North facing and a large east facing window too. There is an unused fireplace in the lounge. Windows are double glazed and the cavity wall along the 36ft length is foam filled. Floor is concrete (non insulated)

There are 3 rads fitted, dining area is 600x800 double, mid lounge is 600x500 double and under the south facing window is a 400x1400 single.
Quickly looking at an online chart gives around 11800btu/h for all the rads.
All rads do have trv's fitted but are wound fully open. RF Room stat is in the lounge area set for 21 deg for this test.

6am with an outside temp of 6 deg and a room temp of 15 deg the stat was set to 21 deg and manual heating.
by 6:30 is was 16 deg, 7am was 17 deg, 7:30 was 17.5 deg and 8am still just 17.5 deg.
So just 1.5 deg raised in 2hrs. The trv's are staying open, I checked them. The boiler is not staying fired all the time which I believe is correct, once the return water reaches a certain temp I would expect it to cease heating until the return temp drops.

My original gas ch system had much bigger rads and didnt struggle like this one does, the installer suggested the rads now are much more efficient so can be downsized without a problem.

Thoughts please anyone....

 

[namsag]

Providing your boiler stat is turned up high enough.
You already know the answer , the rads are not big enough and need enlarging.
The books used to have a definition of what ch is and what back ground heating is.
Ch should be able to raise a room to 21 degrees in an hour if the outside temp is minus one.

 

[robertito]

Do the radiators in the lounge get really hot to the touch, like those in the rest of the house ?

 

[oldman2]

Boiler stat is one division from flat out, rads in lounge are too hot to touch when the boilers firing. Lounge has now reached 19.5 deg after more than 3hrs heating.

Being but a layman I wanted confirmation from the skills here that others also were also of the opinion that the rads were undersized for the room before I go back to the installer.

I wonder if I have any leverage to get the rads upgraded without cost to me as the design spec was obviously incorect at time of install?

 

[kevindgas]

in my opinion if the installer messed up and you just let him design the system for you, then the installer should bear the cost of putting it right.
I have only ever had to change 3 radiators in 20 years because of this problem and took it on the chin so to speak each time.
get him back to put it right

 

[stevebamford]

Have you worked out what the rad BTU should be ? There are quite a few online calculators that will give you an idea

http://www.hamiltonit.co.uk/Tools/RadiatorSizeCalculator.aspx
http://www.radcalcs.com/

In your case these both come up with approx 27,000 BTU (These calculators are both approximations and I made some assumptions in your figures) - I much prefer the first link (but thats coz I wrote it !)

I had exactly the same issue with our new install and did eventually get the rads upsized eventually. (2 swapped for bigger ones and one new rad)

I mentioned figures from the above calculators to the original installer plus I had another quote which detailed the BTU he would have fitted. Both indicated the rads fitted were too small

Original installer rectified the problems for no charge

 

[Agile]

Steve, the way you have written that it sounds as if you went for a quote which included smaller rads than another firm were quoting.

I would have smelt a rat and done some calculations!

I appreciate that they did eventually upgrade it at no further charge. You were lucky there!

Tony

 

[oldman2]

I used several calcs today and got between 16000 and 21000 (yours steve) The total for whats fitted is around 11600btu.

I think I'm going to suggest he replaces a 1400x400 single rad he fitted in place of my old 2500x600 double with something close to what was there.

A 2600x400 double will give around 11600btu on its own so add that to the other 2 in the room that total 6700btu and I hope it will be enough.

Many thanks for all the quick replies, I put in a call to his office but im not going to be top of his to do list

 

[stevebamford]

Hey Tony,

Only one quote specified the radiator sizes and I ended up not using that company

The company I used didn't mention radiator sizes in the quote - I assumed that he had worked out the sizes and the system would heat the house OK

And yeah I count myself v lucky that he came back to sort it out

cheers

s

 

[gas4you]

I've just calculated it on the industry standard mears calculator.

3 outside walls, cavity insulation, 2.4M ceilings = 15700 btu's.

I would add an extra 10% for the open fireplace and possibly 10% for the large window and patio doors, depending how large they really are.

This gives 18840 btu's. Mears are known to err on the oversizing slightly, but this is what I would size the rads for

 

[oldman2]

Thanks for that Dave. Yes the windows really are very large and the patio doors are full room width and height.
Looking at the previous calcs and yours its looking like the 2600x400 double @ 11666btu will fit the bill as the other 2 existing total 6900btu giving me 18566btu total.

There will be a slight imbalance of heat output due to the south facing rad being 11666btu and the other 2 being mounted more or less in the middle of the room length with nothing near the large patio doors but thats how it was before the new system went in and it didnt cause a problem then.

Grateful for the assist guys.

 

[oldman2]

System installer arrived, I showed him the chart of temp rise/time taken.

It was 15 deg room temp @ 6am with outside being 6 deg through to 20 deg by 10:30am when calling for 21 deg.

He said "so the problem is your short 1 degree then?"

I said that I would have thought the system should be able to reach 21 deg room temp in around one hr even with an outside temp of zero.

Hmmm... was the reply.

I had already written out all the data inc room sizes, btu calcs etc and gave him the sheet explaining again that the rads seemed undersized for the room.
His suggestion was to change the 1400x400 single rad for a double as it would double the btu output, I suggested he should consult the btu tables for his manufacture of rads (heatline DD).
He's gone away to recalc the room and rad sizing, but my feeling is he's going to come back offering to change the 1400x400 single for a double, this is an easy way out as no pipes to alter but im sure it will still be undersized.

I just realised I was reading the wrong line in the btu chart for this 1440x400 rad.

My 1400x400 rad is in fact a single panel single convector and I was reading the double panel single convector lines, so the current rads btu's are even lower by 1428btu.

My reading of the rad btu chart gives at 50deltaT 1400x400 single panel single convector 3344btu and the double panel double convector he is suggesting 6281btu so just 2937btu more than at present.

So with a room target btu of minimum 16900btu rising depending on who's calc you use even using his suggested double panel double convector plus the 2 already fitted gives 13196btu which is still well short of the suggested minimum.

I know I'm going to have a problem convincing him but imo the safest bet to reach the required figures would be to replace the 1440x400 with a 2600x400 double panel double convector 11666btu giving around 18000btu total for the room. Or even 2400x400 giving 10768btu giving a total of 17683btu.
Plenty of room under the window for this length as he took out a 2500x600 double from there when he started the job!

 

[John506]

Problem solved

The rads in my rented flat are too small, they don't heat the bedrooms at all, complained but the landlord said he won't pay for them to install bigger because no one else has complained.

 

[stevebamford]

Just keep at it I guess and keep it amicable

Did his initial quote specify the rad sizes ?

 

[oldman2]

Yes his original quote did include the rad sizes but he didnt stick to them when it came to the job and he forgot the middle lounge rad in his quote so added a cost for that later without spec.

I would like to know if someone can explain the rad btu tables list deltaT60 deg and 50deg with a big difference in output depending on which figure you use. Are these temps at the rads? So the boilers running at 70/80 deg for these numbers.

Are you better off running the boiler water temp at highest or is this just going to cause problems quicker in hard water areas with exchangers blocking? Any gas cost savings at different boiler temps?