match a burner to a boiler

[quisut]

Hello

In all manuals supplied by burner manufacturers, there is a graph diagram usually marked 'working field' which shows combustion chamber pressure in millibar or pascal, on the Y axis, and burner output on the X axis. The information in the graph is critical when seeking to match a burner to a boiler. Does anyone know how the information is interpreted? For example, is the chamber pressure shown the actual pressure, or the difference between its and the atmospheric pressure outside of it. I would appreciate any information because every manual I have come across has this diagram and I don't know how to use it.

 

[migoplumber]

boiler output curve is the entire shaded in area showing possible outputs ( which is all we are interested in )
then add the burner to boiler which you will spec to be high end of boiler output or lower end as necessary.
install burner. each burner has different fan +ve pressure. each boiler has -ve chamber and flue pressures.
when burner is in and running you can measure with manometer exactly the chamber pressure.
from there you can plot the exact point on graph if you wish to.

the graphs are there to give you an idea where to start from with respect to your wanted kw output, and match burner accordingly. remember boiler flue burner in that order and you'll be right

its more complicated than that if you want to be perfect. just like rad sizing.

 

[quisut]

Thanks for that, Shaun.

Are you saying that the pressure measurement should be taken when the burner fan is running, and can the reading be expected to be roughly in the range shown on the working field diagram; ie, close to zero millibar (perfect vacuum) or slightly above?

Also, is this measurement taken in the combustion chamber and if so, is it with the intake fan running but no flame?

 

[migoplumber]

the test point will be on the burner, hopefully we are both talking about larger boilers with force draught burner. the pressure in the boiler chamber is taken with the fan running, typically youll find 2 - 3 mbar or +ve pressure in boiler chamber, varies enormously key factors are size and extent of flue.
you can always cross check by gas rating appliance working out the kw that way.