I'm looking for clarity about electric towel rails/radiators and wattages. Hope you can help.
I want to connect a heated electric only towel rail into a circuit that has a smart home 'puck' switch rated for a maximum of 400 watts.
Our bathroom requires roughly 1700 BTU (500W), according to online calculators, for a short period. There is a limited amount of underfloor heating so I'm keen to meet as much of this as I can with a towel rail, balanced against size and style.
I've read about how the delta rating affects the stated heat output of radiators in BTUs. The BTU figure is then often converted into watts. The products I'm looking at range from 1503-1649 (439-482W).
However this isn't the required input wattage, that is clearly governed by the element inside.
I've learned that the appropriate element is given by diving the (delta50) output wattage by 1.81 https://www.designerradiatorshowroom.co.uk/product-category/accessories/elements/ https://www.onlyradiators.co.uk/blog/buying-guides/dual-fuel-towel-rail-buying-guide
My question is basically is this right, why, how is it possible?! It seems bizarre to me to use a 250W element to meet a 500W heating need. Presumably the radiator never gets close to it output rating? I guess the only way it does this is by being on twice as long? What am I missing? Or, to look at it another way how does a 250W element product over 482W of heat?
I presume this has something to do with BTU (energy) and W (power) and time but I'm baffled. Will my 400W switch be ok?
Please can someone explain?
Writing to the radiator vendors and makers has so far not gotten me an answer!
Thanks in advance for any thoughts you have.
A supplier has told me
"The Delta/BTU only relate to a radiator that is on central heating and wouldn't apply to an electric radiator. A 400w would simply build up too much pressure and put your radiator at risk of blowing. The element won't change the heat that is generated in the radiator. The watt of the element is due to it being a closed system and nowhere for the excess pressure to be released. The element will produce the heat output that is determined by the rad surface area, not on the size of the element. It will build temperature to the maximum without causing to much pressure and resulting in the radiator leaking or even worse bursting! A 150W element is recommended for this electric only radiator."
I'm still baffled by this logic and would really like to understand it.