Worth replacing an old oil boiler?

[John Rumm]

Conventional wisdom was that the smaller fully loaded boiler will be more efficient. However that assumed non modulating boilers. It also assumed no pump run on. So each time the boiler cycled, the (considerable) residual heat in the large lump iron HE would be left to waft out of the flue.

With a modern boiler it will load match much based on the actual demand (if it has a decent modulation range - not so true for oil boilers), and the pump run on should at least dump the residual heat into the heating system (and newer boilers typically having lighter HEs there is less of it anyway)

[tabbypurr]

Stupid, adj.: one who asserts a point of view without bothering to even get the facts.

It was about 2m higher up than I was. It might well experience a little more wind, but not much more.

NT

[tabbypurr]

Strange. Last time I looked there were lots for around £100. Maybe it' s the time of year.

NT

[tabbypurr]

It depends on the boilers. Modern wins over historic, greatly so if the old boy is cast iron.

NT

[John Rumm]

Or worse, other bill payers...

[Fredxxx]

The efficiencies of boiler on full output, reduced/modulated output and cycling is less obvious that it used to be.

All boilers are now fan flued so there is minimal passage of air within a boiler when not lit.

That suggests a cycling boiler with a fanned flue is not as bad as an old boiler where natural convection within a boiler would carry heat away.

I might suggest a boiler running in modulating mode might be most efficient from a slower flow of hot gases over the heat exchanger leading to better heat transfer.

Its then not so obvious which is the more efficient, one running at max or one that is cycling.