underfire

Verb

1. To heat from below.
   • 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,...
2. To intentionally operate a boiler, furnace, oven, etc., at a low level.
   • 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...
   • 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,...
   • 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. - 1989, Roger Loison, Pierre Foch, André Boyer,...
3. To burn fuel at less than the desired level, thus not providing heat efficiently.
   • 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...
   • 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. - 2012, Eugene Silberstein, Residential Construction Academy: HVAC, 2nd edition,...
4. To fire at a low (or excessively low) temperature.
   • You no longer need to underfire your products or guess at their high temperature behavior simply because of lag in furnace technology. - 1973, Ceramic Industry, volume 101, numbers 2–6, page 68: