Hello,
Sorry if this is a silly question but why do boilers have two ratings, e.g. 15-21kW? Is this their output at their lowest setting at output at their highest setting?
I am looking to buy a new boiler and I can see a couple of potential models, one is 15-21kW and the other is 15-26kW. If the 15-26 covers all of the range of the 15-21 and then some, does this mean it is a better buy as it will give me extra capacity?
Does running a boiler at the low end or high end of its range cause it to be more or less efficient? I'm sure I remember reading something about efficiency varying according to load but I can't remember what.
I had a quick read of Ed's boiler choice faq and though it helped with other questions, I couldn't see the answer to this.
Thanks.