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NG Boiler Fuel Control

This is an excerpt from the

thread from ‘Dave in QCA’ about his system:

“However, I may have it

set up to fire at roughly 300-350K to take advantage of slower and longer

steaming cycles.  300K BTU firing rate is what is needed (by calculations)

to keep the rads heated to 70% of their capacity.”

Which bring me to the

question(s) I have thought about for a long time but I don’t think have had

answered on The Wall or in Dan’s books.

Is it better to have short and fast cycles or long and slow cycles?

I believe that I have read many posts by people using different size oil nozzles to control the create the ‘long and slow’ effect. And I think this is what NG users mean by ‘down-firing’ their boiler, or using a 2-stage burner.

So is there data to show that down-firing is better for fuel consumption?

And if so, since I have a NG boiler that I believe to be only 1-stage, do I have any way to down-fire it?

Is it simply by controlling the size of the NG inlet pipe to the boiler?

Can this be done with a valve that can be used to increase or decrease the NG input over time?

In my head it makes sense to use a smaller flame for longer to keep the radiators hot for longer but using the same amount of fuel – but is this really possible to calculate and balance?


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    downfiring for economy

    ideally the gas supply pressure is matched to the manufacturers specifications, using a combustion tester, so that all fuel admitted to the burner is completely burned. some down-firing can be achieved, in the 10-15 % range. the burner and boiler are matched to the total of radiation [edr], and not to the previous boiler, or the building heat-loss

    the thermostat or other control will determine the length and frequency of the cycles, and not the burner.

    the boiler must fire long enough in each cycle to supply steam to all the radiators simultaneously. generous main [not rad] venting is needed for this. if the building is tall, then the risers should be vented as well. with a good low-pressure gauge, the back-pressure of venting will be 1 ounce while the air is being gently pushed out of the steam chest, and pipes.

    do a search here for down-firing, and edr. 

    you would benefit from the steam books available from the shop here-get them all, and you will be able to do many things yourself, and also determine the level of expertise of any contractor you choose.--nbc
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