Sizing Water Heating Systems for Laundry Applications

How many gallons per hour do you need?

This is determined by the number of washers and the gallons of hot water used for each hot water setting.


(10) 18lbs. washer

(10) 25lbs. washer

(10) 50lbs. washer

Each washer should state the number of gallons of hot water it uses per cycle. For examples sake, lets assume each washer requires the following gallons per cycle:

18lbs. = 10gal./cycle

25lbs. = 20gal./cycle

50lbs = 40gal./cycle

Now, take the number of washers, times the gallons/cycle to get the total gallons per wash cycle.


(10) 18lbs. washer: 10units x 10gal./cycle = 100gal.

(10) 25lbs. washer: 10units x 20gal./cycle = 200gal.

(10) 50lbs. washer: 10units x 40gal./cycle = 400gal.

Total = 700gal.

What is the recovery rate?
This is the number of cycles per hour, per washer.

A typical washer will run 2 cycles per hour, (25min. per cycle). This includes allowances for loading and unloading. For our example, the following gallons per hour of hot water is needed based upon 2 cycles per hour.

18lbs. washer: 100gal. x 2 cycles/hr. = 200gph

25lbs. washer: 200gal. x 2 cycles/hr. = 400gph

50lbs. washer: 400gal. x 2 cycles/hr. = 800gph

Total gph required = 1400gph

What is your temperature rise?

Your temperature rise is the temperature of the water coming from your faucet in the winter time and the desired temperature needed to wash clothes. The typical washing water temperature is 120ºF and we will use a 45ºF inlet water temperature.

120ºF – 45ºF = 75ºF temperature rise.

How many BTU’s are needed?

BTU’s/hr (Output) = GPH x Temp. Rise x 8.33

= 1400 x 75 x 8.33

= 874,650 BTU/hr output needed

BTU’s/hr (Input) = BTU/hr (output)/heater effieciency

= 874,650/0.80

= 1,093,312 BTU/hr input required

Based on our calculations a model # B11G is required, which has 1,100,000 BTU/hr input.

Note: The possibility of all the washers being run during a given period diminishes as the quantity of washers increase per individual store. The total BTU’s/hr required may be reduced according to the chart below:

0-30 washer – requires 100% of total input BTU’s/hr calculated

31-50 washer – requires 90% of total input BTU’s/hr calculated

51-65 washer – requires 85% of total input BTU’s/hr calculated

66-80 washer – requires 76% of total input BTU’s/hr calculated

Another adjustment can be made based upon your stores uses of hot water. For example, if your machines only use hot water 50% of the time maximum and cold water the other 50%, then you could reduce your required input BTU’s/hr by 50%. But be careful. Its better to have too much hot water capacity than not enough.

Tank Sizing

Take the number of gallons/hr calculated previously x 0.30.

Tank size = 1400 gph x 0.30 = 420 gallons

This is your required tank size. Use either an Ace Model “SW” or “SD” glass lined tank.