9 hours ago
(This post was last modified: 8 hours ago by confused2.
Edit Reason: Spelling
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The boiler and pipework around it loses almost as much heat as a small radiator .. a great start is put the boiler where that heat is wasted so for 3 useful radiators you're actually heating 4 .. you're down to 75% efficiency already.
The installer will assume you need to heat the entire house when the temperature outside is -5C .. which happens (in the UK) for just a few days a year and usually the entire house isn't heated .. so efficiency is determined by how little heat the boiler can produce rather than by how much. Most modern boilers can give less than than their maximum output but it can still be too much. If the boiler output is too high the boiler will heat for a few minutes (or less) .. shut down and fire up again a few minutes later .. this 'short-cycling' can help to reduce efficiency by 10-15%.
The theory behind condensing boilers is that you've paid to heat the flue gas so you should try to send it out as cool as possible.. which (in theory) should be cool enough that water vapour condenses out .. hence 'condensing boiler'. The trick is that the exhaust gas is cooled by the 'return' water from the radiators so the thermal efficiency is dictated by the temperature of the water returning to the boiler .. not the 'flow' temperature as it leaves the boiler. If you know nothing and your heating system was set up by idiots then reducing the flow temperature is always a safe option .. you'll only lose about 10% efficiency.
Simple thermostats which cycle the room temperature up and down can help to reduce efficiency .. in two ways. In general the heating will be off for half the time .. so it has to run hotter while it is on .. and .. the perception of room temperature tends to be of the lowest temperature so the average temperature has to be higher. In the UK many radiators are fitted with thermostatic radiator valves .. when the room temperature is below the set point water flows freely through the valve .. through the radiator and back to the boiler .. so the return temperature tends to be close to the flow temperature and the boiler may never actually run in condensing mode. 'Good' thermostats are outside the scope of this post .. suffice it to say that high price is no guarantee of quality.
A further 5% (or more) is harder to see .. very few installers will insulate pipework where it can't be seen.
As a rule .. a 'traditional' UK central heating system will be closer to 50% efficiency .. nowhere near the claimed 94%.
The installer will assume you need to heat the entire house when the temperature outside is -5C .. which happens (in the UK) for just a few days a year and usually the entire house isn't heated .. so efficiency is determined by how little heat the boiler can produce rather than by how much. Most modern boilers can give less than than their maximum output but it can still be too much. If the boiler output is too high the boiler will heat for a few minutes (or less) .. shut down and fire up again a few minutes later .. this 'short-cycling' can help to reduce efficiency by 10-15%.
The theory behind condensing boilers is that you've paid to heat the flue gas so you should try to send it out as cool as possible.. which (in theory) should be cool enough that water vapour condenses out .. hence 'condensing boiler'. The trick is that the exhaust gas is cooled by the 'return' water from the radiators so the thermal efficiency is dictated by the temperature of the water returning to the boiler .. not the 'flow' temperature as it leaves the boiler. If you know nothing and your heating system was set up by idiots then reducing the flow temperature is always a safe option .. you'll only lose about 10% efficiency.
Simple thermostats which cycle the room temperature up and down can help to reduce efficiency .. in two ways. In general the heating will be off for half the time .. so it has to run hotter while it is on .. and .. the perception of room temperature tends to be of the lowest temperature so the average temperature has to be higher. In the UK many radiators are fitted with thermostatic radiator valves .. when the room temperature is below the set point water flows freely through the valve .. through the radiator and back to the boiler .. so the return temperature tends to be close to the flow temperature and the boiler may never actually run in condensing mode. 'Good' thermostats are outside the scope of this post .. suffice it to say that high price is no guarantee of quality.
A further 5% (or more) is harder to see .. very few installers will insulate pipework where it can't be seen.
As a rule .. a 'traditional' UK central heating system will be closer to 50% efficiency .. nowhere near the claimed 94%.