I have 12 loops that seemed not balanced at all when we bought our place. I bought 12 cheap LCD thermometers (20 Euros or so) with sensor on a wire and pasted these to the return flows. From there on, I started to adjust the flow in the loops in order to get them all to the same return temperature (with the bathroom loop a bit higher). My thinking was and is, that if the return temperatures are the same, the individual loops get enough energy supplied at the front end to get the same return water temperature. Maybe this also works for your radiators.

@potatoman this article from Toodles should be very helpful in light of your recent request.

Posted by: @mphb

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I have 12 loops that seemed not balanced at all when we bought our place. I bought 12 cheap LCD thermometers (20 Euros or so) with sensor on a wire and pasted these to the return flows. From there on, I started to adjust the flow in the loops in order to get them all to the same return temperature (with the bathroom loop a bit higher). My thinking was and is, that if the return temperatures are the same, the individual loops get enough energy supplied at the front end to get the same return water temperature. Maybe this also works for your radiators.

It is probably better to balance each radiator to achieve the desired room temperature, since the heating capacity of each radiator is unlikely to be directly matched to the heat loss of that particular room.

In a room with a physically smaller radiator the opening of the lockshield valve, and hence the flowrate through the radiator, will need to be greater to achieve the desired room temperature.

 @derek-m Perhaps I should have worded my guide a little more precisely; when I said

‘Once the radiators provide proportionate amounts of heat for the rooms, allow the system to settle for about a day.’

What I was trying to indicate is that the heat from each radiator should reflect the heating needs of the rooms they are in. I suspect I am also guilty of thinking that the installers have done their survey thoroughly and accurately and that each radiator is very close to optimum capacity for the room it is fitted in. This of course may be fanciful - but isn’t this why we have the MCS so they can ensure the the installers do their job well? 😉 

Tongue-in-Cheek, Toodles.

Unfortunately the type and size of heat emitters is determined by the proposed LWT, the available space and the room heat loss calculation, with the later being very subjective.

@Toodles  I used a similar method to this last October and it works a treat. One thing I did find very helpful is a thermometer with a logging capability so you can see how each room behaves over a 24/7 timeframe, so fine tweaks can be made if necessary :-).
Logging thermometers are also great for getting to know your systems heating characteristics. For example, our house takes approx 4 - 5 hours to heat from 19.5 to 21 degrees so I know to set my smart thermostat to 13-30hrs to start heating to 21 degrees, so when the Wife sits down to watch the tele at 7pm she is not cold and I have not had to have the heatpump running all day to maintain 21 degrees (19.5 is our set back temp which is ok for the morning but not evening)

@technogeek Yes, I invested in 8 Govee logging thermometers (logging in the sense that they have Bluetooth capability and can send the log to my iPad for scrutiny.) Regards, Toodles.

@derek-m I was probably very fortunate inasmuch that the eight radiators we needed to replace with greater capacity ones could all be fitted within the wall space we had available; by using K2’s, in most cases, they were no higher or longer than the ones we removed. I’m a bit of a ‘don’t mind what it looks like, will it do the job properly?’ type of person and so is my wife - we find pragmatism has great advantages! Regards, Carefree Toodles.😉

I have just carried out your advice and I am within .5c of whatever the Rads I want at maximum in relation to room temoerature. How do determine WL ON THE FLOW C of Heat pump. presently 44c and has been 50c for some years.
Is it just a case of whether they reach the thermostat setting of what ever I am asking ?

@alfapat Well done, you are well underway but keep the LSV spanner/key handy for any tweaking you might wish to carry out later! Yes, see how the comfort level is for a day or two and if all rooms are still warm enough to your liking, then you might wish to lower the (what I know as leaving water temperature and I think you know as water law) another degree then wait and see. If you find that most rooms are still at your comfort level but perhaps one has become just a tad cool, you can tweak that LSV open a ‘nadgers’ [very technical term there!]. You can rinse and repeat until you find that the whole house is starting to drop slightly below your comfort level for all rooms. You then just take the LWT/WL up a degree again! Keep us informed how things go. The final stage may be to adjust any rooms that you wish cooler when there is solar gain or for ‘cooler at nightime’ such as a bedroom using a TRV. Regards, Toodles.

Thanks ! Head banging , haha !