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Radiator Question

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

Last Post by JamesPa 2 hours ago

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DREI

(@drei)

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Joined: 2 months ago

Posts: 68

Topic starter 27/10/2025 5:37 pm

I’ve been working through hundreds of radiator options trying to finalise the design for my heat pump remedial work. My current “designer” radiators are underperforming by around 35% at a 50 °C flow, which obviously isn’t ideal for low-temperature systems. I’m aiming for a 45 °C flow, and anything lower would be amazing.

My main challenge is the kitchen, which only has two available wall spaces: one can take a 2200 × 1000 mm vertical radiator and the other a 2200 × 800 mm. Together, they need to cover a heat loss of roughly 2000 W. Which is proving difficult to achieve.

At the moment, I’m comparing Stelrad and Ultraheat models:

I prefer Stelrad, as they’re MARC members, so their outputs should be more accurate.
Ultraheat aren’t MARC certified, and their published outputs seem noticeably higher, even for similar radiator sizes, which makes me a bit sceptical.

Another concern is that I heard, that vertical radiators don’t perform as efficiently in practice, only the lower sections do the real work since they heat rising air, while the top half tends to do nothing.

Here’s what I’ve calculated and what my options are:

Ultraheat 2000 × 600 Type 22: T50 = 11,419 BTU = 919 W → two units = 1838 W → shortfall = 162 W (≈ 8%)
Stelrad 2000 × 700 Type 22: T50 = 10,246 BTU = 825 W → two units = 1650 W → shortfall = 350 W (≈ 17%)
Ultraheat 900 × 1000 + 900 × 800 Type 33: 11,778 BTU + 9423 BTU = 21,201 BTU = 1991 W → shortfall = 284 W (≈ 14%)

So even with Type 33s, I’m still slightly under, but closer to target.

Would it make more sense to go with the 900 mm high Type 33s, rather than the tall 2000 mm Type 22 verticals? Would there be a better convective/output performance?

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JamesPa

(@jamespa)

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27/10/2025 5:50 pm

Posted by: @drei

↑

Would it make more sense to go with the 900 mm high Type 33s, rather than the tall 2000 mm Type 22 verticals? Would there be a better convective/output performance?

Vertical rads are less effective per unit area, I assume (but dont know for certain) that they factor this into the quoted performance

Other than that I cant comment further, I think its as much a question of aesthetics as anything else. All of them are large so are going to make a significant impact both visually and on wallspace (which can matter in a kitchen!). Have you considered a fancoil. I faced a similar problem in the living half of a kitchen/living room and, after much agonising, ended up with a Mitsubishi Ilife2 slim fancoil. Expensive (but then so are type 33 rads) but worth it in the particular situation and, as it has its own thermostat, it will turn down (but without restricting flow or system volume) when the heat of cooking adds to the energy input to the room. In a kitchen kickspace heaters (which are fancoils) are also an option.

This post was modified 3 hours 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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DREI

(@drei)

Estimable Member Contributor

Joined: 2 months ago

Posts: 68

Topic starter 27/10/2025 6:06 pm

Posted by: @jamespa

↑

Posted by: @drei

↑

Would it make more sense to go with the 900 mm high Type 33s, rather than the tall 2000 mm Type 22 verticals? Would there be a better convective/output performance?

Vertical rads are less effective per unit area, I assume (but dont know for certain) that they factor this into the quoted performance

Other than that I cant comment further, I think its as much a question of aesthetics as anything else. All of them are large so are going to make a significant impact both visually and on wallspace (which can matter in a kitchen!). Have you considered a fancoil. I faced a similar problem in the living half of a kitchen/living room and, after much agonising, ended up with a Mitsubishi Ilife2 slim fancoil. Expensive (but then so are type 33 rads) but worth it in the particular situation and, as it has its own thermostat, it will turn down (but without restricting flow or system volume) when the heat of cooking adds to the energy input to the room. In a kitchen kickspace heaters (which are fancoils) are also an option.

These sound the same as the Jaga units @downfield mentioned in another post. If they work then I am definitely tempted, issue is that I have no electrical connections anywhere near them.

This is what we have at the moment in the kitchen on the two walls, this one is located in the living room side, by the front door. I need a beefy replacement radiator for this one too, but wanted to look at the kitchen options first.

Large panel radiators are not going to look nice, but what choice do I have, if I want the heat output to cover the heat loss. Underfloor heating would have been great, if only the previous owner thought of it when he replaced the whole downstairs with marble flooring.

This post was modified 3 hours ago 3 times by DREI

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JamesPa

(@jamespa)

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Posts: 3193

27/10/2025 7:18 pm

@drei

Thats a nice designer radiator which it would be a shame to bin, and the space is otherwise useless. That said vertical panel radiators dont look so bad, the strong vertical lines take over. There are also various aftermarket treatments including at least one which is a smart metal overlay in three forms, basically designed to make it look like a completely flat panel with or without a 'border'.

Whats the deficit (with the current rad) in watts as opposed to percentage and is it actually that significant given cooking, output from fridge etc. Is there any scope for a bit of 'import' from adjacent rooms. Is there any scope for additional insulation or an additional small rad.

In my utility room I had a similar conundrum and a similar (but narrower) designer radiator. I decided to take the risk that it would 'do' with the knowledge that, if necessary, a supplementary rad would fix up any deficit. The risk paid off.

This post was modified 2 hours ago 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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