Sorry for the digression, but the science tickles me!As far as BTU's against Watts is concerned, it's the same as pints against litres. They are both measurements of the same thing, it's just one is, I guess, imperial, the other is metric.
Technically, BTU and Watts measure different quantities - BTU is a measurement of energy, whereas Watts are a measurement of power - i.e. energy divided by a unit of time - specifically 1 Joule / second.
What is listed as BTU on these companies websites, should really have the units BTU/h.
And the interesting bit..
The definition of a BTU, is the amount of energy required to raise the temperature of 1lb of water, by 1 degree F.
This turns out to be just over 1000J (1055J).
A BTU is almost metric anyway!
The only difference, whereas Watts are Joules per second - to derive power, BTUs are usually divided by hours.
Hence...
1 Watt approximates 1/1000 of a BTU x 60 x 60
1W approximates 3.6 BTU/h ( actually 3.41BTU/h).
Anyway, I find it interesting!