What is a condensing boiler and what are the advantages and disadvantages?
A condensing boiler is a hot water heating device that recovers energy normally released into the atmosphere through the flue (the pipe that usually goes through the wall and will often ‘puff’ war air out), making the boiler more efficient and environmentally friendly.
- When a condensing boiler is working at peak efficiency the water vapour produced by the burning of gas condenses back into liquid water – hence the name “condensing boiler”.
The boiler uses a heat exchanger so that incoming air or water cools the exhaust, forcing the condensation of the water vapour it contains; this heats the incoming air (if an air-to-air heat exchanger is used) or pre-heats the water (if an air-to-water heat exchanger is used).
- A small proportion of the extra efficiency of the condensing boiler is due to the cooling of the exhaust gases, but the majority of the energy recovered is from the condensation of the water vapor in the exhaust gases.
The actual operating efficiency of a condensing boiler depends on the ambient air temperature and the relative humidity. If the incoming air is at 100% relative humidity, the condensing boiler will operate at its maximum efficiency (since it can – in theory – condense all the extra water vapor introduced by combustion).
They should use condensing boilers in Thailand, it’s bloomin’ humid there!
- As the relative humidity falls, so will the actual efficiency of the condensing boiler (because less of the water vapor produced can be recovered from the exhaust).
