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Trying to choose between 2 towel rads - which one should I go for?

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

Last Post by AdamK 9 months ago

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AdamK

(@adamk)

Honorable Member Member

Joined: 10 months ago

Posts: 195

Topic starter 26/03/2025 2:35 pm

trying to choose between 2 towel rads. one is smaller has 25mm pipes 4.07L of water content and apparently chucks out 670W @50c. the next one is more expensive is taller but has 22mm pipes holds 6.2L of water and apparently outputs 493W @50c. why the descrepancy in output? surely a larger overall rad with more water content outputs more heat? i will be running it on a system designed for 40c at -3.1c outside so will likely see a lower than design temp in the room but its the biggest rad i can fit.

https://www.heatandplumb.com/acatalog/reina-eos-curved-heated-towel-rail?variation=20406

https://ukradiators.com/products/aston-stainless-steel-heated-towel-rail-h1800mm-x-w500mm-curved?_pos=5&_fid=d6849b306&_ss=c

This topic was modified 9 months ago by Mars

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JamesPa

(@jamespa)

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Joined: 3 years ago

Posts: 3723

26/03/2025 2:44 pm

Possibly 25mm Vs 22 mm pipes. Output depends on surface area principally, but also on form factor. A rad that is twice as tall as another will emit less than twice as much.

Plus measurement margin of course

Output typically varies proportionally to DT^1.3 where DT is the temp diff between the average radiator temp and the room temp. If the 50C you quote is actually DT, output will be 25%. If the 50 you quote is the input flow temp then output will be 55%. Both assuming room temp of 20 and flow-return dt of 5

This post was modified 9 months ago by JamesPa

This post was modified 9 months ago by Mars

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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AdamK

(@adamk)

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Joined: 10 months ago

Posts: 195

Topic starter 26/03/2025 6:53 pm

Posted by: @jamespa

↑

Posted by: @adamk

↑

trying to choose between 2 towel rads. one is smaller has 25mm pipes 4.07L of water content and apparently chucks out 670W @50c. the next one is more expensive is taller but has 22mm pipes holds 6.2L of water and apparently outputs 493W @50c. why the descrepancy in output? surely a larger overall rad with more water content outputs more heat? i will be running it on a system designed for 40c at -3.1c outside so will likely see a lower than design temp in the room but its the biggest rad i can fit.

https://www.heatandplumb.com/acatalog/reina-eos-curved-heated-towel-rail?variation=20406

https://ukradiators.com/products/aston-stainless-steel-heated-towel-rail-h1800mm-x-w500mm-curved?_pos=5&_fid=d6849b306&_ss=c

Possibly 25mm Vs 22 mm pipes. Output depends on surface area principally, but also on form factor. A rad that is twice as tall as another will emit less than twice as much.

Plus measurement margin of course

Output typically varies proportionally to DT^1.3 where DT is the temp diff between the average radiator temp and the room temp. If the 50C you quote is actually DT, output will be 25%. If the 50 you quote is the input flow temp then output will be 55%. Both assuming room temp of 20 and flow-return dt of 5

both are delta T50 apparently, one is recalculated from a higher flow temp to be more realistic it says on the site.

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JamesPa

(@jamespa)

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Posts: 3723

26/03/2025 7:26 pm

Posted by: @adamk

↑

both are delta T50 apparently, one is recalculated from a higher flow temp to be more realistic it says on the site.

In that case output at 40C will be 25% of quoted value, ie not a lot.

Towel rails appear to be like this, options if not enough are

add an electric element
fit a standard radiator and a rail over (they exist)
ignore the problem and allow heat from other rooms to make up the difference (the one I chose)
fit a standard radiator in addition to the towel rail

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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AdamK

(@adamk)

Honorable Member Member

Joined: 10 months ago

Posts: 195

Topic starter 27/03/2025 11:51 am

Posted by: @jamespa

↑

Posted by: @adamk

↑

both are delta T50 apparently, one is recalculated from a higher flow temp to be more realistic it says on the site.

In that case output at 40C will be 25% of quoted value, ie not a lot.

Towel rails appear to be like this, options if not enough are

add an electric element

fit a standard radiator and a rail over (they exist)

ignore the problem and allow heat from other rooms to make up the difference (the one I chose)

fit a standard radiator in addition to the towel rail

im thinking of going for the taller one and letting the heat from the plant room plus the flow/return 28mm and the primary 28mm's that are in the ceiling all do there bit, as ive had a rad in a bathroom before and they tend to rust quickly. also the room is insulated on all sides including the floor and ceiling.

👍

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