UNIT HEATER SIZING: "CARPENTER'S RULE"

Carpenter's rule is an easy way to determine the heat loss from a building. This provides you with the amount of BTU's per hour required for unit heater sizing. After calculating the amount of BTU's per hour, you reed to decide how many heaters are required. Heaters should be placed to discharge air along the outside walls in a circular pattern. The formula below shows horizontal throw and BTU's per hour which you need in selecting the correct size and number of units.

Carpenter's Rule: H = (0.02 NV + G + W/4) Ti - To

where:

H =	Heat loss in BTU's per hour
* N =	No. of air changes per hour (usually 1-3)
G =	Glass area + door area ­ (sq. ft.)
W =	Wall + ceiling area exposed to outside (sq. ft.)
V =	Volume of room (cu. ft.)
Ti - To =	Temperature difference between indoor and outdoor

Note: Size unit heater for final temperature range of 100 deg. F to 130 deg. F

* AIR CHANGES TAKING PLACE UNDER AVERAGE CONDITIONS
(NO AIR PROVIDED FOR VENTILATION)

Rooms:

1 side exposed to the outside	---	1 change per hour
2 sides exposed to the outside	---	1 1/2 changes per hour
3 sides exposed to the outside	---	2 changes per hour
4 sides exposed to the outside	---	2 changes per hour
No windows or outside doors	---	1/2 to 3/4 changes per hour
Entrance halls	---	2 to 3 changes per hour
Reception halls	---	2 changes per hour