In a fired furnace system having a convection section, and in which control a furnace draft is vital to both fuel conservation and avoidance of furnace damage, apparatus for monitoring the pressure conditions (draft) inside the furnace comprises a first pressure sensor means positioned at the arch (roof) of the furnace, a second pressure sensor means inside the furnace downstream from the convection section, and differential pressure measuring means connected between the first and second means for constantly measuring the pressure drop through the convection section. Alarm means are provided on the pressure drop measuring means to indicate increase or decrease in the pressure drop in the convection section, so that changes in burning conditions, which cause a greater pressure drop or less than normal, and which would result in either significant fuel loss or furnace damage or both if not immediately corrected, can through attention-requiring alarm, cause the required immediate correction to be made as fuel-firing conditions warrant adjustment of draft control means where the term "draft" is in reference to the condition of less-than-atmospheric pressure within the furnace.