GENERAL SELECTION PROCEDURE
1. When the heat loss or heat gain in Btuh for each room is not specified, it should be calculated in accordance with the methods outlined in the current ASHRAE Guide.
2. Determine the number of outlets needed per room. At least one supply for each exposed wall in each room should be used for heating, except that only one supply may be used in bedrooms which have less than 7,000 Btuh heat loss and are located over a heated space. Select at least one heat outlet for each 8,000 Btuh heat loss or 4,000 Btuh heat gain for a room, whichever is greater. The use of several small supplies, each handling moderate air volumes, in place of using fewer and larger supplies may be necessary for better air distribution, and will cut down dirt streaking.
3. The Btuh delivery required for each room supply is determined by dividing the total room heat loss or gain by the number of outlets.
4. Refer to the Heat Conversion Chart on page 18 to find the CFM that will deliver the required Btuh at the desired supply air temperature.
5. Select from the performance data the type and size of diffuser that gives the desired air pattern (spread and throw), at the CFM.

It is usually standard practice to use the cooling conversion chart for year round air conditioning, unless the heating requirements are larger, as the larger CFM required for cooling can be dampered down (lower than fan speed, etc.) for heating. Make sure the pressure loss is within your blower capacity.

All tests used in compilation of performance data in this website were conducted under isothermal conditions (supply air and room air termperatures being equal), therefore, the throw data will be slightly greater for heating and slightly less for cooling.