Gas heat cfm = heat-x input btu x heat-x eff.* / 1.08 x unit heat rise

* If blower motor is in the air stream add its btu to heater output btu

Heat-x output = heat-x input rate x heat-x eff.

Rating in a heat-x for time - sec/ft3 =  corr. factor** x 3600 (sec) x (btu/ft3 gas corr^.) / heat-x btu input

^Corrected gas content = actual gas content x gas content corr. factor^^

Flue loss = a comparison between the CO2 reading and the flue temperature (see chart ansi std Z21.47)

Heat-x efficiency = 100% - heat-x flue loss % 

Corr. factor (Gas temp & bar. press. )** = corrected  barometer*** x 520 / [(gas temp + 460) x 30]

Barometer Corrected *** =( barometer – temp correction) + gas press to Hg”  ^*(example .52Hg” for NG)

o    ^* .52”Hg = NG @ 7”, .81” Hg = LPG normal fire @ 11”, .96” Hg = LPG high fire @ 13”

Gas content correction factor ^^ 

From wet to dry = (btu/ft3 wet gas content) x 1.0177

From dry to wet = (btu/ft3 dry gas content) x .9826

Gas pressure to inches of mercury^* – inches of water x .07355   (example: 7” x .07355 = .52)

Over fire rate – 1.25% gas pressure increase = heat-x input rate x 1.12 for NG or 1.09 for LPG

Air free CO = ultimate CO2 / actual CO2 x actual CO

PPM converted to % CO – take ppm reading and divide by 10,000 (or move decimal 5 places to the left)

Ultimate CO2 = 

Natural gas - [(actual gas content – 970) x .003846] + 11.7

LPG - [(actual gas content – 2466) x .001184] + 13.73