Very high BTU radiator recommendations for heat pump

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Hi folks. I'm trying to spec some radiator upgrades to improve our heat pump efficiency. In summary, it was commissioned to run at a 55degC flow temp, and it basically works fine with all radiators we have at that temp, and bills seem to be similar as gas was last year. However, it would be more efficient at a lower temp - eg 45.
Looking for a reasonable compromise between heat pump efficiency and radiator costs

I have the MCS spreadsheet, which gives all the BTU/Wattage requirements at various flow temps - but obviously, as the flow temp drops, the radiators need to be bigger. At 40 deg flow temp, some rooms would need up to 18000 BTU! So i'm probably aiming for 45deg flow temp, but even then they need to be pretty high output. I was looking at stelrad k3s, which may be ok in some places, but in some places there's just not enough space.

Thoughts/questions:
- are there any good value, good quality 4 column high btu radiators?
- I've seen the 'Reina Wave Horizontal Aluminium Radiator' giving a BTU of 13188, but never heard of them - are they any good?
- any other recommendations for high BTU
- steel or aluminium? (they system is basically always on at a low temp)

I've heard that vertical radiators aren't quite as good, but in some places we may need to use them due to room shapes

I've considered underfloor water heating, and it's probably best, but haven't managed to get any quotes yet and I imagine it'll be pretty disruptive and expensive

Thanks for any thoughts/suggestions
 
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Hi. adding hot aircon could actually work in this room - but i think really the solution is getting more heat output from radiators, and slowly adding more insulation to the room. This room also has a section thats double height, so another two options there are adding a fan to move warm air back down, and also lowering the ceiling a bit (with insulation above)

in the end, most rooms we can just get a bit bigger, and swap some around. In a couple of room, i think we'll go for tall aluminium radiators that seem to give out plenty of heat.
 
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If at all possible I would advise against adding vertical rads as their heat output is mostly in the upper half of the room and I feel this gives little comfort.
 
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Thanks @Agile - I did read that somewhere, but it's whether it's better than nothing! (well, better than an undersized horizontal one....)
I'll try and avoid if possible though....
 
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Try to stick to one measurement system to avoid confusion, preferably kW which has been the industry standard for about 40 years ;)

Kartell K-rads from Crown DIY Halifax are available in a good range of sizes, up to 3m in length and 900mm high. I've found their K2s are fine in most situations. I've got one K3 in my house which is an Ultraheat brand.
 
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At 40 deg flow temp, some rooms would need up to 18000 BTU!
It's not the room temperature that determines the heat requirement. I think you should decide the heat needed, then look at rad output, kW/m2 at various flow temperatures. Pick the preferred temperature and thus find rad area. If that leads to a too big rad, have to compromise by choosing a higher temperature.
 
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Another vote against vertical rads. I moved into my small 1930s semi in 2019. It's a bit leaky and doesn't have cavity walls but it has a 24kW boiler which should be ample; and indeed the first-floor horizontal rads get toasty quickly. But the three vertical ones on the ground floor are hopeless in a cold snap - when you really need them. Trusted local Gas Safe bod says it's not unusual with vertical rads. Where possible I am changing them next year when the weather allows.
 
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@fixitflav yup, I have pretty good heat loss calcs and can see the BTU/Watts required at different flow temps from 30 to 65 degrees. 30 means basically filling every available wall with a radiator! Think I'm targeting 45.

@muggles thanks for the tip on Kartell 90cm tall radiator - those I think will actually work well in places. Currently they have huge discounts on their site, but I'm not sure if that is just a marketing ploy. Either way, in a few rooms, switching from 60cm to 90cm tall radiators will give the extra heat I need and the pipes out the floor can stay in the same place
 
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yup, I have pretty good heat loss calcs and can see the BTU/Watts required at different flow temps from 30 to 65 degrees. 30 means basically filling every available wall with a radiator! Think I'm targeting 45.
OK, it's just that you said "At 40 deg flow temp, some rooms would need up to 18000 BTU!" which seems to imply the 18000 BTU is a consequence of the 40°.
 
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