what size water heater should i use?

[midoriseito]

i am working with gods katrina kitchen in gulf port mississippi.
we have a 12 unit apartment building that we are using for storage and sleeping areas for short term volunteers who come down to help with katrina relief.
my question. we want to get six bathrooms in working order. what size gas water heater would be best to run 6 bathrooms? i am not use to commercial plumbing. more into residencial repair and remodeling.

also, as far as coast, would it be better to use more than one heater? so far i have priced 100gls at 1200--4000 depending.
thanks for your time
danny

[Java_Bob]

will depend alot on the number of shower facilities

[Java_Bob]

found this

o Choose the Right Water Heater for You...

1. Determine whether your family is Low Demand or High Demand. You should consider your family to be High Demand if...
* There are more than two full baths in the home.
* There are (or will be) teenagers living in the home. It's a fact: teenagers use more hot water for showering and washing clothes.
* If you have an oversized whirlpool bath or other large tub. As a rule of thumb, the water heater tank capacity should be 100% of your bathtub capacity (example: 75-gallon tub / 75-gallon water heater).
2. Find your Family Size and Demand Profile in the chart below, and read across to find the First Hour Rating Requirement for your family. If you decide your family is High Demand, consider moving up to the next First Hour Rating level.
3. Consult the charts on respective water heater specifications for an A.O. Smith residential gas water heater with a First Hour Rating that meets your requirement.


FAMILY SIZE FIRST HOUR RATING REQUIREMENT
2 People 45 - 55 Gallons
3 People 55 - 65 Gallons
4 People 65 - 75 Gallons
5 People 75 - 85 Gallons
6 People 85 - 100 Gallons
7 or More People 100 or More Gallons

Remember, these are general recommendations...your A.O. Smith Water Heater Specialist can review your family's needs in even greater detail to make sure the model you choose will always provide enough hot water to meet the demand.

[LazyPup]

Anybody interested in a system that could supply all 12 bathrooms using standard contractor grade residential water heaters and maintain peak fuel economy too?

In a typical residential structure even though they may have multiple bathrooms the likelyhood of all showers being operated at the same time if very slim. On the other hand, this structure is intended to be used by a crew of people who work together and probably share the same duty hours so their is a very high probability that they would all get out of work and want to hit the showers at approximately the same time. We must then design a system that can maintain all the showers simultaneously.

While Danny is only asking to get 6 units online, none the less, they have 12 apartments so let us design for the worst case, 12 showers simultaneously.

Each shower is rated at 2.5gpm and a shower is typically 10 minutes for an anticipated demand of 2.5 x 10 = 25gal per shower. That would then be 25gal x 12 showers = 300gal of water.

Most people prefer a shower at about 90 to 110degF but the Plumbing Codes limit residential hot water distribution systems to a maximum of 120degF. This means that in a typical residential system we are heating about 90% of the water we consume in our showers which results in the water heater running out of hot water fairly quickly. There is a simple solution. (Note the attached illustration).

For Danny's apartment complex we begin by installing two 75gal water heaters in series then we set the calling temperature on the water heaters to 160-180degF.

We then install a "Whole house tempering valve" that will take the 160-180deg hot water from the tank and blend it with the 45-60degF cold water to produce an output mix of 120degF into the hot water distribution system. We are now getting approximately a 50/50 blend of hot & cold which means our initial 150gal of stored hot water will deliver 300gal at the code maximum of 120degF.

We then install a return line from the end of the shower loop and a circulator pump to insure the lines will stay filled with hot water for instant on service at all points of demand. The return line is then fed back into the first water heater. In this configuration during periods of low demand only the first water heater will fire because the water entering the second heater is already at the second water heaters calling temp thus there is no energy consumption in the second heater.

Durring peak demand the first water heater is firing and if its capacity falls below the demand temp the water entering the second water heater will be slightly below the second water heaters set point and the second water heater will automatically fire. The advantage here is the temperature differential between the water entering the second water heater and its set point will still be within its recovery rate thus we double the firing rate but we don't need any expensive or sophisticated control system.

in an absolute worst case scenario even though the water heaters would not be able to produce their full 160deg output, the output they do produce is still above the code max 120degF so we enjoy a limitless supply of hot water.