it would be sensible to buy a tractor that had sufficient horse power and power take offs that were suitable for the machinery it would be used with. It would also be sensible to compare running costs and maintenance costs of the various tractors that were suitable.
People who can afford to buy Bentley generally are those with enough money to pay for the fuel. That said there are Bentleys that do not do many miles, the owner using their more economical small car for most short journeys. ( not many Bentleys in Sainsburies' car park ).
A decent shower needs at least 20 kW of heating into the water. Keeping an average family house warm requires at most 5 kW. Hence a combi boiler has to be efficient at 20kW and at 5kW. In reality the range can be from 2 kW to 40 kW ( large shower and small well insulated house )
Almost all boiler manufacturers quote a single efficiency figure for their boilers. This will be the highest efficiency the boiler can obtain. Probably this is measured in a laboratory set up heating water. The boiler being supplied with the coldest mains water supply to get the most cooling / condensing of flue gases. The more informative graph of efficiency against heat output is not readily available to the general public.
A boiler with high efficiency over a range of from 2 kW to 40 kW would be difficult to produce at a price that domestic customers would accept. Also it would be complex and likely to require higher skill levels in maintaining / servicing / repairing.
A boiler with a range of from 2 kW to 5 kW could have high efficiency over the entire range without being over complicated and thus could be produced at a price the domestic market would accept. Being a less complex boiler would mean maintaining / servicing / repairing costs would be lower.
Using a heat store of some sort to store up heat from a 5 kW boiler and then release it in some way to provide 40 kW of heat into water for a shower enables a less complex boiler to be the heat source.
