Radiator airflow diverter

 

A diversion from the recent solar power theme...

...A couple of our radiators are directly below windows with curtains. When the radiators are on the warm air from the radiators causes the curtains to lift...

 

Radiator off: curtain vertical	Radiator on causing curtain to lift

 

...in effect the radiator is doing a great job heating the space behind the curtain and a less good job on heating the room with probably 2 different impacts:

 

• Comfort: room is slower to warm up
• Cost: the air temperature adjacent to the window is higher and so there is greater loss through the windows.

 

Can this be easily fixed?

 

I found this device on Amazon:

 

Radiator Airflow Diverter

 

I bought a couple and fitted them on these two radiators below windows/curtains - literally a 2minute job - as you can see below the curtains no longer lift.

 

With airflow diverter the curtain no longer lifts even when the radiator is on

 

I was pleasantly surprised that I can feel the airflow coming into the room, even about a foot away from the radiator, so I can believe that the speed up the room warming up (but have not measured it). What about the saving in energy costs?

 

I took some (crude) temperature measurements behind the curtain, with and without the diverters fitted:

• 3 separate measurements
• Outside temperature in the range of 4 to 7degC
• Room temperature in the range of 17.5degC to 18.5degC
• Temperature behind curtain 2.1 to 2.5degC difference with and without diverter (with diverter below room temperature and without the diverter above room temperature).

 

Taking:

• U value of our double glazing as 2.5 W/m2K
• area of the window as 2.8m2
• The radiator on time as 6 months x 14hours/day x 50% duty cycle
• Gas price as 7p/kWh

 

Then I got £1.4 per year per window saving. Given the cost of each diverter was about £30 then the payback time is around 20 years.

 

I must admit that given that I could feel and see the difference (airflow in to the room and curtain lift) then I was a little disappointed that my cost saving estimate was so low and tried to look for incorrect assumptions:

 

• U value (a few websites give this type of figure (eg https://chameleon-decorators.co.uk/blog/u-values-for-windows/)
• Outside temperature - a lower temperature would increase losses through the window and so temperature difference across the curtain (with diverter installed). Conversely, a higher temperature would lower the temperature difference across the curtain - I think that the outside temperature on the day of my tests was a reasonable average for months with heating on
• Radiator on time - if anything this is high and perhaps I should have calculated radiator on time when the curtain is closed?

 

It is possible that better distribution of warm air in the room will also save energy, so potentially this is an underestimate.

 

I think that as a rough order of magnitude the estimate is OK - unless anyone can spot an error?

 

Summary: radiator diverters are, I think, good for comfort, and do make savings on energy bills, albeit with a long payback period.