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Knock on effective of balancing radiators

Bash · 2026-02-23T09:15:37Z

Or HP was installed a few weeks ago and is running really well, the installation was spot on. Our installers will be coming back to balance the radiators and I am trying to get my head around as to the best approach. We have 11 radiators, all designed for 21c and are sized correctly. The house is warm and comfortable, although the bedrooms run a little warmer than the downstairs. I'd like to push more heat downstairs and take some from upstairs to get a better balance of heat that'd we'd prefer. I know how to balance them through the LSVs, but I'd like to understand the if I can achieve the heat balance I'd like, if this is possible and the knock on effect on the system as a whole. We have good volume, probably about 130-140 litres. The installers (who are great) suggested using the bedroom TRVs to controle the bedroom temperatures. We only have TRVs in the bedrooms. Is it better to use the LSVs to reduce the flow or let the TRVs do this? I am conscious that if the TRVs close we lose that volume from the system. Is it better to have less flow permanently by closing off the LSVs a bit and what is the consequence of this on the system as a whole? We have an 8kw Daikin Monobloc, which requires about 50l minimum volume. We also have a 25l volumiser. I know balancing is a very important part of a HP install and I don't want to make it worse chasing the best comfort at the expense of the whole system!

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Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls

Last Post by JamesPa 2 months ago

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 4634

24/02/2026 9:01 am

Posted by: @bash

↑

What is the rough amount of flow that I'll get from the first quarter turn, would it be around half?

It's very dependent on the lsv, heat geek did a series of experiments (search for 'valve authority') and found the control range varied from 0.25 turns to 2 turns depending on model.

This post was modified 2 months ago 2 times by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Mars

(@editor)

Illustrious Member Admin

Joined: 5 years ago

Posts: 4474

24/02/2026 9:19 am

Posted by: @bash

↑

I was starting to come to the conclusion that that FRVs whilst useful, could end up being the best part of £1000 to fit and I don't really want to pay that

We’ve covered some of this over DM, but for everyone else following along, there’s potentially a “smart” alternative to FRVs due to hit the market later this year. Different manufacturer, different approach. I’ve signed an NDA so can’t share specifics, but the key point is that it dynamically balances the system in response to real heating demand rather than relying on static pre-set flow limits.

On conventional FRVs, our experience has been mixed. In principle, they’re a tidy solution. Do the room-by-room heat loss, calculate the required litres per minute, set the valve accordingly and they should hold that flow rate regardless of pressure fluctuations elsewhere in the system. In practice, they did a reasonable job for us at “normal” flows.

Where it became problematic was at very low flow rates. When we tried throttling certain radiators down to around or under 0.5 L/min, the valve didn’t appear to modulate… instead it effectively shut the radiator off. We saw this repeatedly at settings below roughly 1 L/min across five rads. The radiator would go stone cold, forcing us to increase the setting to over 1 L/min, which was more than that emitter actually required from a design perspective.

So while FRVs can be useful, particularly in systems with pressure variability, I don’t think they’re a silver bullet.

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bobflux

(@bobflux)

Estimable Member Member

Joined: 2 months ago

Posts: 73

24/02/2026 10:05 am

I find it quite ironic that most of this heating/plumbing business is about controlling flow and pressure, without actually measuring flow and pressure! Strange rules for a game, when you think about it...

Now a ultrasonic heat meter costs 20€ in medium quantity on alibaba... Motorized ball valve costs 10€... Pressure sensors are also quite cheap... The call of over engineering is too hard to resist 🤣

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JamesPa

(@jamespa)

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24/02/2026 10:18 am

Posted by: @bobflux

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I find it quite ironic that most of this heating/plumbing business is about controlling flow and pressure, without actually measuring flow and pressure! Strange rules for a game, when you think about it...

Thats a very astute observation. Its like an electrician working without any test equipment!

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Morgan

(@morgan)

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Joined: 5 years ago

Posts: 698

24/02/2026 10:41 am

I'm looking for a cap to replace the TRV. Whilst all of mine downstairs are fully open, I'm given to understand that there is still pressure on the valve that constricts the flow. I want to remove the TRV but not leave the valve exposed. All I see are decorator caps that achieve the opposite by completely closing the valve. Ideas please.

This post was modified 2 months ago 2 times by Morgan

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
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2 ESS Smile G3 10.1 batteries.
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Bash

(@bash)

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Posts: 163

Topic starter 24/02/2026 10:58 am

@jamespa

I found the valve authority video which is very helpful.

We have Pegler Terrier valves, but I cannot find any info on what the valve authority is like on these.

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JamesPa

(@jamespa)

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Joined: 3 years ago

Posts: 4634

24/02/2026 11:00 am

Posted by: @morgan

↑

I'm looking for a cap to replace the TRV. Whilst all of mine downstairs are fully open, I'm given to understand that there is still pressure on the valve that constricts the flow. I want to remove the TRV but not leave the valve exposed. All I see are decorator caps that achieve the opposite by completely closing the valve. Ideas please.

Decorators caps, not screwed down (they can actually be used to adjust the flow) or the original head just balanced on top. I do the second of these but if you have children or dogs they will get knocked off so perhaps in this case the first is better.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

👍

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