Sizing:
To size your Hot Water heater, you need to determine what the maximum Hot water usage is for your Laundromat, assuming that every washer is run on a Hot water cycle.  If you have older Top-load washers, then you can figure that each washer cycle will use about 20 gallons of Hot water.  For older front load washers (fixed timer with 5 water changes) you can figure that the total water consumption is 2 gallons per pound of washer capacity.  So a 50 lbs. front load washer will use approximately 100 gallons of water.  The older front loader washers have cold water rinses so only 30% of the water used will be hot water, so that 50 lbs. washer would only use 30 gallons of Hot water per cycle.  The modern front load washers with microprocessor controls use significantly less hot water than the old machines.  If you have modern washers, I would contact your local distributor to determine the exact amount of Hot water consumed per washer, per cycle. 
 

Do the Math:
For example let's assume you have the following washers in your Laundromat:
10 Old Topload washers, (12+ years old); 5 new Top-load Micro washers, (2 years old); 8 old Wascomat 30 lbs. W-124 washers (25+ years old); and 4 new Huebsch Micro 60 lbs. HCN060K washers (2 years old).
Looking at the worksheet (see below), we estimate the hot water consumption of the older washers.  The Top-load Hot water consumption is about 20 gallons per cycle and the front load washers is calculated by multiply the total washer poundage by 2 and then by 30% to get the hot water demand.  We received Hot Water figures from our distributor and entered them into our chart and come up with a total of 448 gallons of Hot water with every washer used for one cycle.  If we now assume the washers are running continuously then we can figure 1.5 cycles per hour.  This assumes 10 minutes of loading & unloading for the washers.  We now multiply in our usage factor of between 60-70%, in this case 65%.  The usage factor assumes that not every washer will be operating on a Hot water temperature setting.  The adjusted usage is now 437 gallons of Hot water per hour.

Requirements:
Now that we know the number of gallons of Hot water, now we go back to our incoming water temperature chart (of last week) and determine the number of degrees rise in temperature required.  If we assume we are in NY and the incoming water temperature is 40 degrees and we want 125 degree water, then we require 85 degree temperature rise.  Most specification sheets for water heaters show the number of gallons with 80 degree rise or 100 degree rise.  With the same heater the number of gallons for the 100 degree rise will be less than the number of 80 degree rise.  We can adjust the 437 gallons at 85 degree rise and multiply by the ratio of (85/80) to give us a 464 gallons based on an 80 degree rise benchmark.   Now go to your heater manufacturers and see what heat produces at 464 gallons of Hot water at an 80 degree rise.
 

Storage Tank Size:
In vended Laundromats, you will need approximately 1/3 of the hourly Hot water demand in Hot water storage.  With this example, 437 / 3 = 145 gallons in Hot water storage.  In this example, I would recommend a 160 gallon storage tank and a high recovery water heater that would produce 450 gallons of 80 degree rise Hot Water.  In this example, I am admittedly am slightly short on my heating capacity 464-450 = 14 GPH shortfall and I would compensate with a slightly larger storage tank (160-145=15 gallons).  When in doubt, call your local laundry equipment distributor.  Your local distributor performs these water heating calculations all the time and they are a tremendous resource to help you operate your business more profitably and with less hassle. 
 

Next week we will discuss the 5 different types of water heaters and what heater characteristic to focus on.