Rate of heating in a living room?

[Mossop]

If a radiator has been correctly sized for a room and the boiler is adequate and fully functioning, at what rate of C/Hour would you want a living room to be able to heat up at?

Thanks.

 

[Mossop]

Thanks gpbeck.

 

[John.g]

So, I've placed black electrical tape onto the two 22 mm pipes under the boiler and that has made a substantial difference when taking the temperatures. I let the boiler run for 40 minutes before taking any temperatures.

Firstly, with just the one radiator in question switched on. On/Off below refers to the "flame" symbol coming on or off on the boiler screen. Boiler temperature on-screen ranged from 48 C - 67 C. So, on average it's turning on and off every 2 Minutes & 25 seconds.

The flow/return at the rad was 45.8 C and 40.6 C (I also used black electrical tape here).

Time:
0:00 On
0:02 Off
0:05 On
0:07 Off
0:10 On
0:12 Off
0:15 On
0:17 Off

Below are temperatures I was getting on the flow/return under the boiler at various intervals:

50.9 - 39.4
47.0 - 40.9
45.2 - 37.9
61.6 - 39.0
49.7 - 38.1
60.3 - 38.5


Separately below is with the radiator still on, but with another couple of rads on the same floor turned on. I left it about 40 minutes or so to allow the other rads to warm up. Boiler temperature on-screen ranged from 57 C - 67 C. So, on average it's turning on and off every 3 minutes 43 seconds..

The flow/return at the rad was 47.5 C and 42.7 C

Time:
0:00 Off
0:03 On
0:08 Off
0:11 On
0:15 Off
0:19 On
0:23 Off
0:26 On

One Rad:The boiler would appearing to be firing for ~ 40% of the time with a average flow temp of 52.5C & return of 39C, based on a min output of 8 kw (post above) then theoretically a average boiler output of 3.2 kw, even if the boiler efficiency is very low while cycling its difficult to see that rad producing its rated output, very difficult to determine anything from a relatively small heat load with a boiler with such a high minimum output.
The second test would indicate firing for 62.5% of the time so theoretically a more believable output of 5 kw with 4 rads on.

I don't think you can really do any more to figure out what the true output of that rad is.

 

[Mossop]

One Rad:The boiler would appearing to be firing for ~ 40% of the time with a average flow temp of 52.5C & return of 39C, based on a min output of 8 kw (post above) then theoretically a average boiler output of 3.2 kw, even if the boiler efficiency is very low while cycling its difficult to see that rad producing its rated output, very difficult to determine anything from a relatively small heat load with a boiler with such a high minimum output.
The second test would indicate firing for 62.5% of the time so theoretically a more believable output of 5 kw with 4 rads on.

I don't think you can really do any more to figure out what the true output of that rad is.

So you're not seeing anything from the figures to indicate that it's a problem specific to the boiler. It's more likely an issue with the radiator and the window?

 

[gpbeck]

One Rad:The boiler would appearing to be firing for ~ 40% of the time with a average flow temp of 52.5C & return of 39C, based on a min output of 8 kw (post above) then theoretically a average boiler output of 3.2 kw, even if the boiler efficiency is very low while cycling its difficult to see that rad producing its rated output, very difficult to determine anything from a relatively small heat load with a boiler with such a high minimum output.
The second test would indicate firing for 62.5% of the time so theoretically a more believable output of 5 kw with 4 rads on.

I don't think you can really do any more to figure out what the true output of that rad is.

I think OP means that is the total run time. Not sure how long it rests before starting up but it’s in the boiler program. He has a big short cycling problem because boiler is oversized and system is not balanced. Rapidly rising return temp cuts it out. He has 2 jobs, balancing all the radiators and glazing.

 

[gpbeck]

So you're not seeing anything from the figures to indicate that it's a problem specific to the boiler. It's more likely an issue with the radiator and the window?

Once more, the radiator is PERFECTLY FINE! Boiler should not be stopstarting like this at all. It is getting too much hot water in the return and cutting out. Balance all your radiators. Set boiler temp to 55 deg and see how long it runs. Slowly increase running temperature until it runs for at least 15 minutes before cutting out.

Draw curtains.

 

[Mossop]

Not sure how long it rests before starting up but it’s in the boiler program.

The times above are in minutes, so it's off for ~3 minutes or so before starting up again.

 

[John.g]

Seems to be a consistent 3 mins off time, certainly agree with new window but all the balancing in the world IMO will not improve the output of that rad as its measured deltaT was only 4C.
Also the shockingly poor modulation means that a min 8 kw heating demand must be maintained to allow the boiler to run continuously.

 

[Mossop]

the output of that rad as its measured deltaT was only 4C.

Presumably the deltaT figure which you refer to is data which a radiator manufacturer can easily provide if I were to ask for this figure from a different manufacturer before purchase (and hoping that the figure which they provide isn't an over optimistic figure). What sort of figure would I be looking for, ideally?

Also the shockingly poor modulation means that a min 8 kw heating demand must be maintained to allow the boiler to run continuously.

Do you think this poor modulation issue is related to the radiator/balancing, or would it be specifically an issue with the boiler?

 

[gpbeck]

Seems to be a consistent 3 mins off time, certainly agree with new window but all the balancing in the world IMO will not improve the output of that rad as its measured deltaT was only 4C.
Also the shockingly poor modulation means that a min 8 kw heating demand must be maintained to allow the boiler to run continuously.

Slowing flow through this radiator will drop its average temperature by 10 degrees or so, 40 degrees hotter than the 11 deg room instead of 50 deg so 20% less heat emission but for 100% more time. If a more continuous flow is delivered through it it will emit more heat overall. OP obviously wants a new radiator but he’ll be disappointed and poorer. He’s certainly not listening to me.

 

[Mossop]

He’s certainly not listening to me.

I don't want to appear that I'm not listening. Ultimately, I have no plumbing background. I'm listening to two different opinions here and, yes I can get the window sorted, but aside from that I don't know if I need a different brand of radiator or if it's just a matter of getting the system balanced or if there's a problem with the boiler? There are no boiler error messages on-screen.

 

[Last Plumber]

I suggest you get a heating engineer in to look at it for you. It shouldn't take much to work out what's wrong for someone experienced who is actually there observing.

 

[John.g]

Presumably the deltaT figure which you refer to is data which a radiator manufacturer can easily provide if I were to ask for this figure from a different manufacturer before purchase (and hoping that the figure which they provide isn't an over optimistic figure). What sort of figure would I be looking for, ideally?


Do you think this poor modulation issue is related to the radiator/balancing, or would it be specifically an issue with the boiler?

Presumably the deltaT figure which you refer to is data which a radiator manufacturer can easily provide if I were to ask for this figure from a different manufacturer before purchase (and hoping that the figure which they provide isn't an over optimistic figure). What sort of figure would I be looking for, ideally?


Do you think this poor modulation issue is related to the radiator/balancing, or would it be specifically an issue with the boiler?

The manufacturer couldn't care less what the radiator deltaT is, his/her only responsibility is to provide or advertise a radiator based on a "50 degree" standard, its quite simple.... a 50 deg rad is the (mean radiator temperature) minus the required room temperature. So if you require a deltaT of 20C (desirable for boiler efficiency) and if you accept that 50C is a reasonably low return temp you would run the boiler with a flow temp of 70C and you then may have to balance the rad or rads to achieve this return temp of 50C but you will then have a (70+50)/2)-20, a 40 deg rad with a output of only 75% of the 50% rad so you should oversize your rad by 1/0.75 or a factor of 1.33, on the other hand, if you are still running with a boiler temp of 70C but if the flow rate is increased to give a deltaT of 4C then your rad becomes ((70+66)/2) - 20, a 48 deg rad with a output of 94% of the 50 deg rad. So back to your famous rad, I think you ran it at 60C with a deltaT of 4C so you should have had a (60+56)/2)20, a 38 deg rad or 70% of its 2.4kw rating at 50 deg or 1.7kw. I think you then got the output up to, can't remember but 2.0 or 2.4 kw?? (see old posts) by raising the boiler temp to 75C.
You can do your own calcs here or just look up a rad factor table if more convenient.
The calculated output = ("known deg" rad)/"50 deg" rad))^1.3, what this means is if you have a 40 deg rad, the calculation is (40/50)^1.3 and so on, you may think that you should have 90% output but you only have 75%.
Now you know as much as any heating engineer does or should.

The boiler is operating as designed, my poor modulation referred to it 8kw output as most 30kw boilers will IMO easily get down to 5 or 6 kw

Would agree with above re different type of rad as there are numerous posts re the (non) performance of "tall" rads, IMHO, all these rads should have a diverter fitted or be plumbed TBOE.

 

[gpbeck]

I don't want to appear that I'm not listening. Ultimately, I have no plumbing background. I'm listening to two different opinions here and, yes I can get the window sorted, but aside from that I don't know if I need a different brand of radiator or if it's just a matter of getting the system balanced or if there's a problem with the boiler? There are no boiler error messages on-screen.

If it helps you, I pretty much agree with John.g.

Balancing will cost you nothing, there’s a thread here on how to do it.

if I saw this system like this without your input, I would conclude someone has turned up a radiator in a cold room, and made it worse.

 

[Mossop]

If your whole system was balanced so each radiator had a 15deg drop you might surprisingly be able to increase boiler flow temp yet lower return temp so increasing overall efficiency.

Balancing will cost you nothing, there’s a thread here on how to do it.

Thanks guys, your input is very appreciated. As I mentioned earlier the flow for this rad is definitely going into the lockshield, and ideally it should be going into the TRV (which is not bi-directional). So I'll get that sorted and then I'll get the rads balanced so they have 15 C drops.

IMHO, all these rads should have a diverter fitted or be plumbed TBOE.

Thanks for mentioning the diverters, as I hadn't heard of those. TBOE (the best of everything?)

 

[John.g]

IF you put TBOE (top & bottom opposite ends)in the search box you will find a lot of info, its supposed to be the best way to plump a rad and it might but its certainly the ugliest. Someone discovered that if you plumbed in rads (like the majority) BBOE (bottom bottom opposite end) that the circulation was just as good almost.
Its almost uncanny how it (BBOE) works, if you have a cold rad with boiler at normal temperature and open the rad valve(s) the hot water will move straight up to the top of the rad along the first 6 ins or so and then gradually heat the rad but from the top down. It would be interesting if you were to shut off one valve on your rad, let it cool down, then reopen it with a hot boiler and see does it behave like the above, it should/might (from the hot inlet side) start heating up the first one or two columns and then gradually move along the top and start heating the remainder from the top down, I think this is why they sometimes fit a diverter plug because it forces the water up the first few columns and it flows downwards then gradually loosing heat.

 

[Mossop]

IF you put TBOE (top & bottom opposite ends)in the search box you will find a lot of info, its supposed to be the best way to plump a rad and it might but its certainly the ugliest.

I've just seen a picture of TBOE at the link below, and yes that is ugly.

What is a heat sink radiator?

A heat sink radiator should be at least 10% of the KW output of the “maximum output to water” of the stove (more if the stove manual says so and I have seen figures as high as 20%).

www.stovefitterswarehouse.co.uk

 

[Ben-gee]

This will work fine if you plumb it correctly ie flow into your uni-directional trv.

Why are we still going on about this?

Re-plumb this rad and balance your system - the report back.

 

[Mossop]

This will work fine if you plumb it correctly ie flow into your uni-directional trv.

Re-plumb this rad and balance your system - the report back.

I'm doing that ASAP.

Would agree with above re different type of rad as there are numerous posts re the (non) performance of "tall" rads, IMHO, all these rads should have a diverter fitted or be plumbed TBOE.

For what it's worth, I've asked the radiator manufacturer and they state that the rad does not require a diverter (or have an in-built one).

 

[John.g]

That's the point " (or have an in-built one) ", as I said above, the diverter is normally only perhaps say 2 columns in from the flow pipe to force the hot water to the top of the rad and it then works normally like any other rad. In the absence of any markings then you don't know if its installed correctly or not (if diverter fitted).

Carry out that test I suggested, shut off one valve, let rad cool down of if already cold, shut the valve and heat up your system, then reopen the valve fully and see if the hot water is moving up the first few columns or is rising up gradually through the remaing ones, also the return shouldn't be too hot until the whole rad heats up.

 

[Mossop]

I've carried out the test and it heats up along the flow side, then across all bars at the top, then from the top down across them all.

 

[John.g]

So, is it first moving all along the bottom to the return (outlet) straight away and is this return hot first or as soon as the others start heating.

 

[Mossop]

So, is it first moving all along the bottom to the return (outlet) straight away and is this return hot first or as soon as the others start heating.

It's 3 bars per column. It appeared to go up the central bar directly above the feed. Then go across the top directly across all at the top, then cascade down heating all at same time. Hopefully, that sounds ok, if not I can repeat and see if I can determine any further detail.
I didn't notice the return heating for some time

 

[John.g]

No, that's fine, that would indicate to me at any rate that its circulating as it should.

One other query, when you took the cycling times tests with four rads and then one, what was the boiler set point temperature?.

 

[Mossop]

One other query, when you took the cycling times tests with four rads and then one, what was the boiler set point temperature?.

It was set to 60C though in reality it fluctuated up and down between, what was it, 55C and 67C ish as it cycled

 

[Mossop]

Does this give any insight into whether a diverter would be beneficial, or best to consider this after the rad feed/supply are switched and 15C drops are added to the rads?