TRVs and towel rads

[Mr_T25]

Hi

1. Is there any truth to white towel radiators having better heat output compared with chrome ones?

2. If I am installing a towel rad in a small W/C area, I know its not a big issue but was thinking of putting a TRV on there. Any reason not to?

3. Having just installed a new combi boiler into a new kitchen, was thinking of adding a small radiator on there. I remember 20 years ago my plumber at the time said not to put a TRV on the first radiator off the boiler and that at least one radiator needs to not have a TRV on there (which our first floor bathroom does not). Does this still hold true about no TRV on the first radiator?

4. Drayton TRV4s - are they the better ones to go for?

 

[John D v2.0]

Is there any truth to white towel radiators having better heat output compared with chrome ones?

Correct, a shiny surface is a low emissivity surface. That's why celotex is shnny. However the majority of the heat is convection so you still get that.

If I am installing a towel rad in a small W/C area, I know its not a big issue but was thinking of putting a TRV on there. Any reason not to?

Better to put a trv everywhere for best efficiency. Maybe looks is a reason not to? Or cost perhaps.

Does this still hold true about no TRV on the first radiator?

In systems with no bypass you'd need a radiator open all the time. But if you have a bypass there's no need most of the time.

PS I'm not a pro, just based on my limited experience

 

[Madrab]

1. Is there any truth to white towel radiators having better heat output compared with chrome ones?

yes, roughly 25% higher output size for size

2. If I am installing a towel rad in a small W/C area, I know its not a big issue but was thinking of putting a TRV on there. Any reason not to?

No reason not to

3. Having just installed a new combi boiler into a new kitchen, was thinking of adding a small radiator on there. I remember 20 years ago my plumber at the time said not to put a TRV on the first radiator off the boiler and that at least one radiator needs to not have a TRV on there (which our first floor bathroom does not). Does this still hold true about no TRV on the first radiator?

As john mentions it's all to do with a bypass for the boiler to ensure min flow through the boiler when all valves are shut - if the boiler is supplied with an internal or there is a separate auto bypass fitted then a rad wouldn't be used. That being said an open rad is not considered good practice these days and an auto bypass should be fitted between flow and return, if one is required by the MI's.

4. Drayton TRV4s - are they the better ones to go for?

They are good TRV's

 

[Mr_T25]

Thanks guys.

 

[D_Hailsham]

You must not have a TRV in the same room as the wall thermostat as they will conflict.

 

[^woody^]

yes, roughly 25% higher output size for size

Do you know why? I didn't beleive, it but having checked, yes it seems that ratings for white rads are better for the same size chrome rad.

I'm curious how a bit of pipe filled with hot water should release more heat if covered in paint than if covered with chrome - especially when neither paint or chrome is a particularly good insulator and the heat it mainly convected. It just seems daft.

 

[John D v2.0]

mainly convected. I

Mainly yes, but radiators do actually radiate a fair bit. If there was a fan pointing at it the protpropor of radiation would drop, but radiation is noticeable if you sit close.
That's how low e foil insulation and space blankets work

 

[^woody^]

That's how low e foil insulation and space blankets work

But that is by reflection from the surface.

With a radiator, heat is moved from the water to the metal by conduction and then once the metal (and coating) are hot, the heat is liberated by mainly convection, and a slight bit of radiation - I would not think anything like 25% more radiation.

So if the radiator as a componemt (water, steel and coating) is heated to a temperature of say, 50°c then how can more heat be given off from the surface if the surface is coated with paint rather than chrome?

I could understand it if the coating was an insulator, but it's not.

 

[John D v2.0]

Emissivity isn't directional, it applies equally whether the reflective is on the warm or the cold side, as long as it's facing a void where radiation would occur.
I don't know the actual figures off hand, but the boundary between a void and a surface has its own R value dependent on the emissivity of the surface. Plus the other side of the void has a R value as well.

 

[John D v2.0]

Well I never....Woody is stumped. Never thought I'd see that happen in the few years I've been on here. Not a smart *rse afterall.

??? The way I see it is no one knows everything, he wants to learn something new, do you consider that a flaw to be pointed out?
I notice you didn't know either and this whole thread is dedicated to helping you

. Is there any truth to white towel radiators having better heat output compared with chrome ones?

 

[Madrab]

The other thing to remember is that a towel radiator isn't very efficient with either convection or radiation anyway given it's construction and shape. It's more of a contact heater.

Normal panel radiator are much more efficient convectors given their shape/construction (especially type 21/22 P+/K2 that have double panels & fins) is designed to channel air up and through from the bottom.

 

[Mr_T25]

??? The way I see it is no one knows everything, he wants to learn something new, do you consider that a flaw to be pointed out?
I notice you didn't know either and this whole thread is dedicated to helping you

It was a tongue in cheek remark to Woody's wit. You didn't get the joke.

 

[John D v2.0]

It was a tongue in cheek remark to Woody's wit. You didn't get the joke.

lost on me

 

[^woody^]

Did I miss something?

Anyway I'm still non the wiser as to how or even why painted rads should release more heat than chromed rads.

I'll have a read up on the finer points of emissivity, but that's really just a name and a rating. What I can't get my head around at a basic level is how a coating of paint lets more heat out of a metal tube (25% more) than a coating of chrome. To me that implies that chrome is insulating the pipe and causing the water to retain its heat. But that can't be so because the heat is being convected into the chrome coating just the same as it would into a paint coating.

 

[denso13]

Anyway I'm still non the wiser

https://industrytoday.co.uk/hvac/why-do-chrome-radiators-have-a-lower-heat-output