Should I make my radiators smaller?
A deliberately provocative title, forgive me.
The question is really about how important it is to have equally sized radiators in each room, in relation to specific room heat loss.
I had a heat loss calculation done, and with my current radiatiors at a design temperature of 50C flow and -3 OT, some are clearly undersized, the worst being -47%. Okay that needs upgrading, no brainer.
But how much to upgrade it, just to 100% the heat loss of that room, or to match the most oversized radiator in any other room?
What if thats not possible, and room A is sized with 100% of power output to heat loss, and room B is sized to 158% of power output to heat loss; I assume room B is going to get much too hot?
The modern advice is not to have TRVs and to go as "open circuit" as possible, so how do we mitigate the oversized radiator in room B? Should we make it smaller? What % of size deviation can be handled without adding flow restrictions and controls?
Everyone seems to say bigger radiators are better, but should that advice come with the caveat that sizing needs to be equal throught the heating zone?
TIA
Bonus question; if you open up all the radiators in a reasonably balanced system, and let the heating come to equielibreum with OT, and measure the temperature within each room; is that a better way to calculate heat loss? Is there a method for that?
Posted by: @scalextrixWhat if thats not possible, and room A is sized with 100% of power output to heat loss, and room B is sized to 158% of power output to heat loss; I assume room B is going to get much too hot?
The modern advice is not to have TRVs and to go as "open circuit" as possible, so how do we mitigate the oversized radiator in room B? Should we make it smaller? What % of size deviation can be handled without adding flow restrictions and controls?
The deviations can be handled by
a) the lockshield valve. this restricts the flow rate through the rad in question which increases the deltaT for that rad which reduces the average temperature and hence the output.
b) the fact that rooms tend to share heat anyway because the thermal separation is poor.
I had mismatches of 150% plus, no problem
Posted by: @scalextrixBonus question; if you open up all the radiators in a reasonably balanced system, and let the heating come to equielibreum with OT, and measure the temperature within each room; is that a better way to calculate heat loss?
No, you wont leave it like that for long enough to overcome all the other variations that mother nature throws at us.
Posted by: @scalextrixIs there a method for that?
yes, (a) measure it over several weeks monitoring individual radiators and the heat pump, Adia Thermal make the kit to do this or (b) plot your gas/oil usage vs average OAT for several months or preferably a whole season, estimate the efficiency of your boiler, and work from there (gives you whole house only).
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.
@jamespa thanks for the reply, so really in this case we have to reduce the flow to the radiator to achieve it.
In my specific case the oversize radiators are upstairs which isn't really the best from a heat sharing perspective, but I get your point.
Posted by: @scalextrix@jamespa thanks for the reply, so really in this case we have to reduce the flow to the radiator to achieve it.
In my specific case the oversize radiators are upstairs which isn't really the best from a heat sharing perspective, but I get your point.
Mine are also upstairs because I upgraded them before I realised how much the heat pump industry overestimates house losses. Still not a problem although the lack of 'valve authority' with the very old LSVs on a couple of the rads in question makes for a slightly tricky, but not impossible, adjustment . Of course that is my house, yours may be different. The 'excess' upstairs capacity helped my installer to be happy to leave the bathroom well under-provided for, thus I could retain my exiting towel rail rather than replace it.
That said if you can make the downstairs ones bigger go for it. Lower flow temperature = lower cost and greater comfort, as you clearly know!
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.
- 22 Forums
- 2,049 Topics
- 44.7 K Posts
- 39 Online
- 3,277 Members
Join Us!
Trusted Installers
Struggling to find a reliable heat pump installer? A poor installation can lead to inefficiencies and high running costs. We now connect homeowners with top-rated installers who deliver quality work and excellent service.
✅ Verified, trusted & experienced installers
✅ Nationwide coverage expanding
✅ Special offers available
Latest Posts
-
RE: Hydronic plinth heaters and ASHPs
@jamespa we should be ok as the model I'm looking at ha...
By benson , 23 minutes ago
-
RE: Renewables & Heat Pumps in the News
Let me add two other points to what @lucia has just pos...
By Transparent , 28 minutes ago
-
RE: Yes, the "zoning with ASHP" topic again...
@harryrea I agree entirely with the concept of zoning ...
By Heatgeek , 2 hours ago
-
RE: Help optimising my system!
@wh0am3ye you’re absolutely right that what you’re seei...
By Mars , 3 hours ago
-
RE: Additional Battery v Wind Turbine v Ripple
There was a call today for Ripple investors and amongst...
By Judith , 19 hours ago
-
@heatgeek I kind of get it… but aren’t you still in the...
By SUNandAIR , 21 hours ago
-
-
RE: Commencing on an ASHP Installation Process
I think you may very well be right and of course A2A ca...
By JamesPa , 2 days ago
-
-
RE: Agile: average import cost vs other tariffs?
@old_scientist We are with SSEN and our G99 application...
By Toodles , 3 days ago
-
RE: Solar Power Output – Let’s Compare Generation Figures
Yes. Storing the solar generation within the home is gr...
By Transparent , 3 days ago
-
RE: ASHP Ecodan L9 error - No Heating but Hot Water
@phoenix15, @heacol cover your area… I’d strongly recom...
By Mars , 3 days ago
-
RE: Warm weather and heat pumps.
@editor Oh nothing right now because $ needed for struc...
By Lucia , 4 days ago
-
RE: Potentially more choice including air to air heat pump grants
@jeff Such documents are far too wordy for my ‘daily re...
By Toodles , 4 days ago
-
RE: Getting the best out of a heat pump - is Homely a possible answer?
@grahaml I cannot agree that it is a small percentage o...
By benson , 5 days ago
-
RE: Samsung Gen6 16kW tribulations
@emceed, can you please give us an update on your syste...
By Mars , 6 days ago
-
What's the problem you are trying to solve. The answer...
By JamesPa , 1 week ago
-
Good luck. For what it is worth my system was very def...
By JamesPa , 1 week ago
-
RE: Massive Electricity Cost for Running My Air Source Heat Pump
I agree @mark-h The Building Regs are now very readable...
By Transparent , 1 week ago