Underfire

It was contended, that the only objection which could be raised against under-firing, was the danger of incrustation, or deposit upon the boiler bottom, of matter held in suspension by the water; but that this rarely, if ever, caused explosions; the utmost injury it occasioned, was causing the boiler plate to be burnt out, and that this effect could not take place, without gross neglect.

The large supply of natural gas at Chicago permitted underfiring the batteries of the Chicago By-Product Coke Oven Plant with a mixture of producer gas and natural gas. […] The mixing of by-product coke oven gas with blast furnace gas to correct the varying thermal deficiencies of the latter when used to underfire coke ovens is patented by Becker.

One of the major factors contributing to high particulate emissions from domestic burners is on-off cycling. […] Underfiring consists of using a smaller (undersized) unit which has to stay on longer and, therefore, cycles less. However, no data are available on the effectiveness, cost, and public acceptability (more complex system or inability to heat house as comfortably during very cold periods) of these proposals.

It is generally accepted […] that underfiring of ovens with lean gas (generally blast furnace gas) leads to a greater heat consumption than underfiring with rich gas.

Often home owners select a [wood] stove that is too hot for the space to be heated. Many stove owners compensate by underfiring the stove, which causes poor performance, increased emissions and potential chimney fires by creosote buildup.

If the burner is underfiring, the nozzle may need to be changed or the pressure at the outlet of the fuel pump may need to be adjusted.

You no longer need to underfire your products or guess at their high temperature behavior simply because of lag in furnace technology.