Boiler Sizing Replacement Guide
4
STEP 2: CALCULATE TOTAL HEAT LOSS
The form shown in Figure 2 (Part of the Weil-
McLain Boiler Replacement Worksheet) can be
used for calculating total heat loss by following
these steps.
1. Based on the type of construction, amount of
insulation, etc., select the Construction Design
Number from Table A below which most
nearly matches each of the areas (levels) to
be heated.
2. Determine the total square footage of each
area to be heated from the Job Survey Form.
Round to the nearest hundred.
3. Based on the Construction Design Number
selected and the square footage of each area,
determine the heat loss (at 70°F design temp.
di.) from Table B (page 5). NOTE: Do not add
in heat loss for basements which are not to be
heated; ignore crawl spaces which are open to
basement areas.
4. If the Outdoor Design Temperature of the city
is unknown, refer to back page. If the design
temperature dierence is other than 70°F,
multiply the heat loss for each area by the
appropriate correction factor from Table C
(page 6). Round to the nearest ten.
5. If it is a two story house, multiply the heat loss
of the first level by the appropriate Ceiling
Correction Factor from Table D (page 6).
Round to nearest ten.
6. Add the adjusted heat loss for each area to
determine the Total Heat Loss.
LEVEL
CONSTRUCTION
NUMBER SQ. FT.
HEAT LOSS
(AT 70°F
DESIGN
TEMP. DIFF.)
CORRECTION
FACTOR AT
°F TOTAL
CEILING
CORRECTION
FACTOR
ADJUSTED
HEAT LOSS
FIRST LEVEL
x = x =
SECOND LEVEL
x =
BASEMENT
x =
SLAB
x =
TOTAL HEAT LOSS
FIGURE 2: HEAT LOSS CALCULATION FORM
TABLE A: CONSTRUCTION CHARACTERISTICS
FRAME CONSTRUCTION BRICK CONSTRUCTION
CONSTRUCTION
DESIGN NUMBER
WEATHERSTRIPPED
GLASS
INSULATION THICKNESS
CONSTRUCTION
DESIGN NUMBER
WEATHERSTRIPPED
GLASS
CEILING
INSULATIONWALL CEILING
Without basement or crawl space With 4" brick & 4" lightweight block**
1 single 1" 2" 14 single 2"
2 double 1" 2" 15 double 2"
3 single 1" 3" 16 single 3"
4 double 1" 3" 17 double 3"
5 double 2" 3" With 8" brick**
6 double 3" 3" 18 single 2"
With full basement or crawl space 19 double 2"
7 double 3" 6"* 20 single 3"
8 double 3" 6 21 double 3"
9 double 3" 9
22†
For Basements- Concrete or block walls
8' high, 6 1/2' below grade (stray heat
from boiler & piping included). Or for
unheated crawl spaces
10 double 3" 12
11 double 6" 6"
12 double 6" 9"
23‡
4" concrete slab with 1"
perimeter insulation
13 double 6" 12"
* With 2” Floor Insulation.
** Furred, lath & plaster.
† Use for basement heat losses WITHOUT fully exposed walls and for floor losses over closed unheated crawl spaces.
For basements with fully exposed walls use FIRST FLOOR heat loss.
‡ Use for grade level slab construction.