Can I work out my boiler efficiency with this method?

Reed_Richards

The water in your tank will generally be stratified with hotter water at the top and colder at the bottom.  So if you have a tmeperture sensor it will only tell you the temperature at that level in the tank.  This may complicate the calculation.  

coffeehound

Reed_Richards said:

The water in your tank will generally be stratified with hotter water at the top and colder at the bottom.  So if you have a tmeperture sensor it will only tell you the temperature at that level in the tank.  This may complicate the calculation.  

The water is churned while being heated due to convection currents, so the measured temperature at that time should be representative.  Don't know what the tolerance on tank thermostats is like, though . .

coffeehound

Verdigris said:

Looking at the performance table assuming I'm running at mid output it was 75% efficient when new, is there a ballpark amount of efficiency a boiler will loose over time?

Looks like my 70% was spot on, allowing for decline in eficiency.

There was an example on here once where a poster accurately measured how much energy his old boiler was using just to heat a DHW cylinder to a modest temperature once a day.  

Turned out it was using 8 kWh of gas to put 1.5 kWh of heat into the tank.  Apparently, old boilers can be horrendously inefficient!

[Deleted User]

It is worth looking at the definitions of net and gross boiler efficiency. The use of net efficiency allows some boiler manufacturers to claim efficiencies in excess of 100%.

https://ianbgas.co.uk/technotes/Gross-and-net-and-weird-efficiency.html

Note the warning at the bottom of the page

1. Older boilers give input figures as gross, but don’t necessarily tell you.

Reed_Richards

coffeehound said:

Reed_Richards said:

The water in your tank will generally be stratified with hotter water at the top and colder at the bottom.  So if you have a temperture sensor it will only tell you the temperature at that level in the tank.  This may complicate the calculation.  

The water is churned while being heated due to convection currents, so the measured temperature at that time should be representative.  Don't know what the tolerance on tank thermostats is like, though . .

That may be true whilst you are heating the water but it won't be true of the start point.  If the tank hasn't been heated for a while the water inside will have stratified so you will be measuring the start temperature just at the particular level in the tank at which your temperature sensor is situated.

coffeehound

Reed_Richards said:
That may be true whilst you are heating the water but it won't be true of the start point.  If the tank hasn't been heated for a while the water inside will have stratified so you will be measuring the start temperature just at the particular level in the tank at which your temperature sensor is situated.

Fair point.  I guess the copper or SS tank that the stat is in contact with will conduct heat so give some averaging across the temperature gradient

JohnSwift10

Verdigris said:

Remember, though, that that pilot light is heating your house,

With a conventional flue I think most of the heat would be lost.

Not in the summer when heating is not required.
I turned off the pilot light for the heating in the summer after I found out how much it was using.

otb666

we replaced our 16yr old boiler and house feels a lot better The usage was lower by 15% this quarter Dont know if thats due to weather and door being  shut more due to lock downs and not going out.  We got interest free loan pay 100pm for 2 years As service plan reduced really paying 70pm.  We are very happy with our decision figured we would get in before they are abolished 

Verdigris

JohnSwift10 said:

Verdigris said:

Remember, though, that that pilot light is heating your house,

With a conventional flue I think most of the heat would be lost.

Not in the summer when heating is not required.
I turned off the pilot light for the heating in the summer after I found out how much it was using.

So how did you heat your water? If you used the immersion heater that would, almost certainly, have cost far more extra, over gas, than the saving from no pilot light.

QrizB

Verdigris said:

JohnSwift10 said:

Verdigris said:

Remember, though, that that pilot light is heating your house,

With a conventional flue I think most of the heat would be lost.

Not in the summer when heating is not required.
I turned off the pilot light for the heating in the summer after I found out how much it was using.

So how did you heat your water? If you used the immersion heater that would, almost certainly, have cost far more extra, over gas, than the saving from no pilot light.

JohnSwift10 previously stated:

JohnSwift10 said:

When I replaced my warm air heating and separate hot water heating ...

So their space heating and water heating systems were entirely separate.