Federal Correctional Institution Hot Water Efficiency

Federal Correctional Institution – 5 x 200 MBTU EHW Units + 1600 Gallon Storage

This project is an illustrative, real-world example of our vetted efficient hot water system installed by GEM approved manufacturers and installers.


A Federal Correctional Institution (FCI) in the Midwestern, United States houses approximately 1,500 people. There are several housing units, each holding up to 400 people. Each housing system is identical in construction and uses the same model and set-up of water heating system. In addition, the water usage is set on a scheduled time during the day.

Current Water Heating System Setup

In each housing, the heating system consists of two commercial 1,000,000 BTU/hr natural gas fired boilers with rated thermal efficiency of 80%. Each gas boiler circulates to a separate 800 gallon storage tank. A 91 GPM pump and aquastat controls the circulation of the water from the storage tank to the gas boiler. Both the units are operated simultaneously for a total installed capacity of 2,000,000 BTU with 1,600 gallons of storage. The aquastat is set at a temperature of 140F. A tempering valve and recirculating pump keeps the water up to the shower heads and faucets hot. This loop is set at approximately 108F.

Efficient Hot Water Setup

Five i200P units with a combined capacity of 1,000,000 BTU/hr were cascaded in parallel feeding into both the 800 gallon tanks was set up to replace both 1,000,000 BTU gas boilers. 2” headers pipes were used for the water inlet and outlets. One significant difference was that the incoming water now flowed via each of the five i200P unites. There was no change on the existing tempering valve or recirculation pump setup. The EHW units were connected using a simple telephone cable (RJ11) and when any unit was programmed for the recirculation time and temperature, it automatically carried over the set parameters to the other units. A 2” return line via check valve brought water back from each of the 800 gallon storage tanks to the inlet side of the EHW units. No external pump of aquastats were needed.

The programmed temperature is 125F and set to come on from 6AM to 9PM in one hour intervals. During this time, the EHW units powered on and brought the 1,600 gallon tank up to 125F. Also, at any given time depending on the amount of flow demanded from both the 800 gallon tanks, one or multiple i200P units fire to replenish both the 800 gallon tanks.

Gas Usage Analysis (43.2% reduction measured)

Two diaphragm type gas meters with a maximum capacity of 2,000 CFH and a +/−2% measurement accuracy were set up — one in the building using the EHW units and the other in an adjacent building using the existing boiler setup. It should be noted that both buildings are identical in construction, have identical occupancy, identical schedules, identical ground water temperature, and same gas source. Gas usage was monitored in both buildings for a period of 31 days.