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Radiator reflectors: are they worth the trouble?

Posted by Tim Pullen on 18 May 2011 at 9:31 am

radiator reflector

Like a lot of things in improving energy efficiency, radiator reflectors can devolve into a complex argument. For example, radiators are not actually radiators. They are also convectors and conductors. And radiator reflectors only deal with the radiant heat.

A single panel radiator will have 50% of the surface area facing the wall. Fins on the back of the radiator will increase heating surface area but also increase the convection effect. Double rads will have only 25% of their surface facing the wall and double finned, double radiators will have the lowest radiated heat emission and highest convection emission.

Complicated isn’t it?

To try and un-complicate the question, we have first to ask two other questions :

1. Is the house, and specifically the walls, well insulated? That is, really well insulated – 100mm plus thickness? If so, there is no benefit from reflectors as the heat is barely escaping through the walls anyway.

2. Are they older, single panel radiators or more modern radiators with fins on the back? If they are older type then reflectors will have a good impact. But they will have a smaller impact on finned radiators.

That is not to say that they should not be installed if you have modern radiators. In terms of saving energy every little helps and reflectors are relatively cheap and easy to install.

Which radiator reflectors to install?

There are plenty of different types out there but the ones with a saw-tooth like surface are the best as they encourage convection and improve the warm air movement around the room.

If you have a poorly insulated wall I would suggest first gluing the reflector to a thin sheet of insulation (Kingspan, Celotex or similar) and fixing that (with glue) to the wall behind the radiator.

Photo by Sarah & Mike Scott

About the author: Tim Pullen is eco-editor for Homebuilding & Renovating magazine, author of Simply Sustainable Homes and founder of sustainable property consultancy WeatherWorks.

If you have a question about anything in the above blog, please ask it in the comments section below.

Comments

5 comments - read them below or add one

Cathy Debenham

Cathy DebenhamComment left on: 20 December 2011 at 12:34 pm

Hi Scott.tb25 - it would be great to hear what exactly the difference in cost was, and how that compares with the cost of buying the reflectors. 

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scott.tb25

scott.tb25Comment left on: 20 December 2011 at 11:33 am

I have recently purchased a 10 radiator pack of Radiator reflector from an online store. I installed the all of the radiator reflectors within 10 mins and work really well in my newly refurbished bungalow. My husband was shocked by the slight reduction in energy bill due to these panels. 

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GreenMike

GreenMikeComment left on: 26 May 2011 at 8:46 am

I fitted the 'saw-tooth' reflector panels over the last winter and saw an immediate improvement in room temperature and heat dispersal as they seemed to speed up convection. I would highly recommend them as a quick simple improvement. Best prices I found were on Ebay.

 Any experts on radiator convection out there? I want to know the optimum  height for the bottom of a radiator? 

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Tim Pullen

Tim Pullen from Weather WorksComment left on: 18 May 2011 at 10:45 am

Walls of the typical house account for 35% of the total heat lost from the building - its why insulating walls is so important. And 50% of the radiators output is directed at the wall. So we get a disproportionately high heat loss through the wall area around the radiator. Thermal imaging shows this up every time.

I agree that reflectors are not a panacea and will not make huge inroads on energy bills. But the impact they can have in relation to their cost - i.e. return on investment - is huge.    

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jtec-energy-performance-nn46da

JTec Energy PerformanceComment left on: 18 May 2011 at 9:56 am

That's a very good summary of their benefits, Tim (or lack of benefit). 

Only one point that I'd like to add, and that is, that they only reduce heat loss through a small proportion of the fabric of the home (the area of external wall that is covered by the radiator).  Heat loss through the walls is, in turn, a small proportion of the total heat loss in a home, which includes the heat loss through the other exposed areas (roof, windows, floor) and other losses like ventilation loss and hot water loss.

So, their effect is only a small proportion of a small proportion, so although they may help slightly, don't expect them to make big inroads into reducing your fuel bills. 

This is why they are not part of the RdSAP methodology used to rate the energy efficiency of homes - they don't make enough difference to make it worth including them.

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