Date: Job Name: Room: Address: Inside Temp (IDT): Outside Temp (ODT): Temp. Difference: Estimator:

Instructions for use of the Residential Btu Estimate form
To determine the amount of heat required to provide comfort in a room or a house, it is necessary to calculate the amount of heat being lost (in Btu's per Hour) when winter conditions outdoors are at the Outside Design Temperature, which is the normal coldest temperature for that area.

Heat is transmitted through all surfaces that will be warm on the inside and cold on the outside. This includes walls, ceiling, floors, windows and doors. If a room on the other side of a wall or ceiling is to have normal heating, then that wall is not considered "cold".

In addition to the outward transmission losses, the infiltration of cold air must be added. Transmission + Infiltration equals the total heat loss, which must be replaced by the heating equipment.

This form is suitable for either an individual room or for an entire house. If several rooms are to be calculated, use an individual sheet for each room.

DESIGN TEMPERATURE

The amount of heat lost is directly related to the Temperature Difference (TD) between the desired Indoor Design Temperature (IDT) and the Outside Design Temperature (ODT). It is usually desirable to maintain 70⁰ inside the room when the outside temperature is at a normal low point. The ODT for each major city is determined by long-range weather readings, and is fixed by the engineering profession. Subtracting ODT from the usual 70⁰ gives the temperature difference for that locality. (Do not calculate TD when using this form, UNLESS the desired Inside Design Temperature is other than 70⁰.)

The heat loss Factors listed opposite the calculation sheet are based on 70⁰ IDT and 0⁰ ODT. In localities where the ODT is not 0⁰, the temperature difference will be either greater or smaller than 70⁰, and so will the calculated heat loss. Conversion Numbers for other ODT's are shown at the bottom of page 4.

APPROXIMATE ESTIMATE OF Btu's per hour RESIDENTIAL HEAT LOSS*

For locations with Zero degrees (0⁰) ODT

(For other ODT's, use Conversion Numbers from bottom of opposite page.)**

Step 1: To determine transmission losses, measure all surfaces which will be warm inside and cold outside. Step 2: To determine infiltration, calculate total volume of heat space. Step 3: Select factors for each category of heat loss - A,B,C,D,E. Step 4: Multiply each total below by the appropriate factor, and add all totals for the TOTAL Btu/Hr.

GROSS COLD WALL (Including windows and doors)
Height x Length = Sq. Feet

Front: L. Side: R. Side: Rear: Gross Wall:

WINDOWS and OUTSIDE DOORS
Height x Width x Quan. = Sq. Ft.

Total: Gross Wall: Subtract A Windows & Doors NET WALL: B

COLD CEILING (attic or roof above)
Length x Width = Square Feet

Total Cold Ceiling: C

COLD FLOOR (over cold bsmt. or crawl space)

Length x Width = Square Feet

Total Cold Floor: D

OR - Floor on concrete slab (cold edge only)
Length + Width + Length + Width = Lin. Feet

Linear Ft. Total Cold Floor: D

INFILTRATION (volume)
Length x Width x Height = Cubic Feet

Total Volume: E

CALCULATIONS

Btu per hour loss at 00 Outside Design Temperature TOTAL

Btu/Hr.

**Conversion Number for other Outside Design Temperature: x

Adjusted Btu/Hr:

* For accurate calculations use the I=B=R Method.

For other types of construction, see additional factors in I=B=R Guide H=21

**For other Outside Design Temperature, MULTIPLY Total Btu/Hr. by Conversion Number.