This month, you should be finalizing any code changes to the international and uniform codes, as all code changes for the 2027 codes are due the first week of January. International Code Council Group A code change proposals — for plumbing, mechanical, fuel gas and residential codes — are due Jan. 8, 2024.

Uniform Plumbing Code (UPC) changes for the 2027 codes have had two different dates published for the submission of proposals deadline. One document says the deadline is Jan. 2, 2024; the other says the deadline is Jan. 12, 2024. I suspect they will honor the Jan. 12, 2024 date. Either way, the code changes are due right after the New Year. Get your code change proposals submitted over the holidays, and you will be stress-free in January. 

Last month, we discussed the codes related to domestic hot water systems. This month, we will continue discussing hot water systems and troubleshooting the cause of many system performance issues or failures. They have led to property damage due to pipe breaks/bursts and personal injury due to thermal shock, scalds and Legionnaires’ Disease. These issues usually stem from the lack of commissioning of hot water systems and the lack of proper design, installation or maintenance. 

Hot water system failures often occur because of one or more key issues: design, installation or maintenance. These three issues are like a three-legged stool: if any one of them has a problem and falls short, the stool will topple. Design, installation and maintenance are important for properly operating hot water systems. 

My experience has been that the lack of proper maintenance is the most common cause of system failures. Many of these failures lead to injuries or property damage, and that’s when I get a call from an attorney asking me to investigate. The following is a list of hot water system startup or commissioning tips and considerations for system designs to avoid performance issues or failures. 

Untrained Maintenance Personnel

Commissioning and startup of hot water systems is important for the designer, installer and building owner. Once the system is designed, installed and commissioned to work as intended, we turn the entire building — sometimes as big as a cruise ship — over to an owner. Who the owner hires to perform maintenance is a critical next step; often, maintenance personnel are hired to do both skilled and unskilled work. 

I have read many depositions where maintenance personnel spend the morning mowing and picking up trash in the parking lots and on the grounds, and the afternoon replacing light bulbs and “troubleshooting” complaints of no hot water. 

As a plumbing professional, you might likely diagnose the cause of no hot water in a few simple steps. However, to the untrained individual, you can see the confusion when the maintenance person finds hot water at the kitchen sink. The next day, with the same complaint of no hot water at an upper-floor apartment, the maintenance person again checks the hot water at the kitchen sink and finds none. 

You would be correct if you said the next step is turning up the water heater thermostat. This cycle repeats itself, and the water gets hotter and hotter; the problem of no hot water is never resolved, and a scald occurs. Coupled with the lack of maintenance personnel trained in plumbing, I have seen poorly designed plumbing systems built for low first cost. However, these systems tend to lack any fail-safe design considerations and generate very high operating and maintenance costs. 

DHW Checklist

Below is a checklist for domestic hot water (DHW) system design, installation and commissioning. It is a tool that can be added to for inspection, troubleshooting and maintenance of domestic hot water systems.

A. Water Heater Types and Sizing Considerations 

1. Storage-Type Water Heaters and Hot Water 

Generator Systems 

a. For each water heater, document: 

Manufacturer

Model number 

Serial number 

Fuel type

Energy input (BTU/hour or kW/hour) 

Gallons per hour (first hour)

Location/room number

Equipment ID

Area or system serviced

Design temperature on drawing (schedule or plans)

Actual operating temperature

Is a thermal expansion tank associated with the hot water system?

Is the thermal expansion tank sized properly for the storage, system piping volume, and temperature rise from cold to operating temperature?

b. If the water heater(s)/boiler(s) are copper fin-tube type, note the circulating pump information and the storage tank size: 

Tank size (gallons) 

Tank temperature setpoint (F)

Circulator pump info heater to tank pump:

1. Horsepower

2. Electric volts/Ph

3. Gallons/minute (gpm)

4. Feet of head pressure @ __ gpm

Note that copper fin-tube water heaters/boilers should be used with a storage tank, boiler-to-tank pumps, and controls to shut off the circulating pumps when the boiler’s burner shuts off. Copper fin-tube water heaters/boilers can only increase the water temperature through the water heater by about 35 F, plus or minus 10 F because of velocity limitations. Too high causes tube erosion, too low causes scaling of the tubes. 

Therefore, tanks should be used for DHW applications to allow multiple passes between the tank and the heater and bring the hot water temperature up to the final setpoint temperature. Always route the cold water supply to the DHW system to the bottom half of the storage tank. Do not route the cold water directly through the copper fin-tube water heater because it can cause erosion of the copper tube, condensation issues and pressure fluctuation problems.

c. Note any other water heating equipment or types of water heaters:

Solar info 

Heat pump info

Geothermal heat pump (loop size vs. demand)

Heat recovery systems

Special operating conditions/temperature notes 

d. Shell-and-tube HW generator with an integral tank: 

Steam press: __/lb/hour 

Heating HW: 

1. Temp: (F) 

2. Area of heat exchanger surface 

Heat exchanger flow in gpm: 

1. Type 

2. Tank size (gallons)

e. Other type water heater with external tank 

Type 

Tank size (gallons) 

Notes 

f. Verify and document that the water heater(s) are sized properly for the building type using one of the following methods:

Manufacturer’s sizing calculations

ASPE Engineering Design Handbook

Industry-approved sizing methods for water heaters 

2. Tankless Water Heaters

If the water heater is tankless: 

Determine the flow rate and temperature rise in degrees F.

Verify if the flow rate and temperature rise are adequate for the application. 

Determine bacteria control/disinfection method (Note: Many tankless heaters do not reach thermal disinfection temperatures at 131 F = 5 to 6 hours for disinfection; at 140 F = 32 mins for disinfection):

a. Maintaining temperatures above Legionella growth temperatures.

b. Chemical disinfection. Determine the manufacturer’s maximum chemical exposure in parts per million and a maximum contact time at that chemical level to avoid excessive corrosion and possible voiding of any warranties. 

Verify and document that the tankless water heater(s) are sized properly for the building type using one of the following methods:

a. Manufacturer’s sizing calculations 

b. ASPE Engineering Design Handbook

c. Industry-approved sizing methods for water heaters

d. Perform a calculation to determine if the manufacturer’s specified flow rate at the required temperature rise will handle the number of water supply fixture units (WSFUs) on the hot water system when WSFUs are converted to gpm.

B. Storage Tank Commissioning

1. Document the temperatures entering and leaving each storage tank: 

Tank inlet: location, size, temperature (F) 

Tank outlet: location, size, temperature (F)

Tank recirculation connection: location, size, temperature (F) 

Note that ASHRAE 188 and ASHRAE Guideline 12 recommend a hot water storage temperature of at least 140 F. A temperature-actuated mixing valve (TMV) should be installed on the outlet of the hot water tank to allow a stable hot water distribution temperature and a hot water return (HWR) temperature above 122 F. 122 F is the maximum Legionella growth temperature.

2. Document the storage capacity and dimensions of the storage type heater or external storage tank or tanks:

Document the location of the storage tank(s): Room name and number

Document the location orientation of the storage tank (vertical or horizontal)

Document the tank diameter and height of vertical or length of horizontal tanks:

a. Storage tank dimensions

b. Insulation thickness and type

3. For horizontal tanks, use 60% of stored volume as usable for first draw. 

4. For vertical tanks, use 70% of stored volume as available for first draw.

5. Test the temperature and pressure-relief valve(s) to see if they are operational.

6. Document the number and size of the temperature and pressure-relief valve(s) and their rated BTU/hour capacity compared to the total BTU/hour capacity of all connected water heaters.

7. Document the tank drain valve(s) size and location and determine if a floor drain is nearby for system drain down. 

C. Domestic Hot Water Circulating Pump

1. Verify the circulating pump(s) are operating, if installed.

2. Verify that the circulating pump is manufactured of noncorrosive materials, such as all-bronze or stainless steel, and rated for domestic water service. 

3. Verify that the circulating pump flow direction is correct (sometimes, they get installed backward).

4. Verify that the circulating pump is rotating in the correct direction (sometimes, the wires are crossed, causing the motor to rotate in the opposite direction).

5. Verify that an electric power disconnect switch or power switch is within 6 feet of the circulating pump or as required by code.

6. Determine the required hot water circulation flow rate in gallons per minute (gpm) to offset heat loss in the circulated portion of the piping system. 

Check the engineer’s calculations, schedules or plan notes. 

If calculations, schedules or plan notes are not available, use 1 gpm for each HWR branch or riser. Add up the gpm as piping collects and returns to the circulating pump. 

Verify the proper flow in gpm and velocity based on the HWR pipe size and the calculated flow in gpm. 

Note that, per the Copper Development Association’s technical manual, for systems with copper or brass (copper alloy) valves and fittings, the velocities should not exceed 5 feet/second (fps) for hot water pipe between 85 F to 140 F. For piping more than 140 F, the velocity should not exceed 2 fps to 3 fps. If these velocities are exceeded, erosion of the copper pipe can occur, and leaks will appear at changes in direction in the piping system.

7. Document the circulating pump head pressure in feet, flow in gallons per minute, horsepower, voltage, phase, pump manufacturer and model number. Determine if the flow and head pressure are adequate for the hot water distribution system.

D. Troubleshooting Circulating Pumps

When there is a large hot water distribution system and users far away have complaints of no hot water intermittently, they call the maintenance person. He often hears “no hot water” and immediately goes to the mechanical room to turn up the temperature on the water heater. This can create a scalding condition. 

Instead, the lack of hot water could simply be that the circulating pump has quit working. Check to see if a power supply switch is turned off, a valve is closed or a strainer is plugged. Sometimes, the impeller is eroded, or the pump motor has failed. If the pump is not running, it will not circulate hot water to the end of the system and will take a long time to get hot water to fixtures far away from the water heater. 

I have investigated many scald cases where the circulating pump has failed, causing a long period of no hot water followed by a blast of hot water (where the maintenance person had turned up the water heater). In large buildings, parallel/standby circulating pumps could be an option. 

E. Aquastats and Timers on DHW Systems 

A debate has been waged among energy conservation and health/safety groups about whether the hot water recirculating pump should run all the time. The energy conservation groups promote turning the circulating pump off at night or during off-peak times. 

There are energy conservation code requirements that require circulating pumps to turn off. Some engineers turn off the circulating pump with aquastats; others turn off the circulating pump with timers. 

I cringe when I see these types of controls turn off the circulating pump because this contributes to conditions that are conducive to bacterial growth. In my opinion, health and safety is much more important than energy conservation. 

Recently, there has been an exception to the energy code requirements for hospitals and nursing homes because Legionella is a real threat to their patients, who often have suppressed immune systems. I always ask the question: Does Legionella bacteria care what type of building it is in? The answer is: No. The bacteria will grow wherever the conditions are favorable for growth. Using aquastats and timers to shut off circulating pumps sounded like a good idea until Legionella came along; now, they do not sound as appealing. 

Using an aquastat to shut off the circulator pump when the temperature is satisfied at the end of the system is a bad idea that allows the system temperatures to fluctuate wildly — by as much as 20 to 30 degrees in some larger buildings. 

Shutting off the circulator pump creates a condition where it is difficult to set the maximum temperature limit-stop on the shower valves. It can also allow the hot water system to cool down during off-peak hours; anyone showering during those hours will get a sudden, significant temperature rise after spending some time in the shower. This has been known to lead to scalding incidents. 

At other times, the system temperature will drop into the Legionella bacteria growth temperature range. I’m not a fan of intentionally creating temperature fluctuations in a hot water system. When weighing between water and energy conservation vs. health and safety, health and safety should always win.

F. Incoming Cold Water Temperature

Document the incoming cold water temperature to the building. The cold water temperature can change as much as 40 F from winter to summer. This will cause limit-stops to be readjusted seasonally to account for changes in the incoming cold water temperature. 

Cold water temperature = F at location

G. Domestic Hot Water Out: Temperature Leaving the Water Heater

Document the hot water temperature immediately after the water heater (at a temperature gauge or at a faucet or hose bibb ahead of the TMV). 

Hot water temperature = F at location

H. Domestic Tempered Hot Water Temperature Leaving the TMV 

 Document the hot water temperature immediately after the TMV (conforming to ASSE 1017 or CSA B125.3), which is the hot water source mixing valve serving the hot water distribution system. 

A temperature gauge should be on the outlet of the TMV. If a fixture branch or a hose bibb is off the discharge pipe downstream of the mixing valve, the water temperature can be checked there to verify the readings on the TMV temperature gauge.

Tempered hot water temperature = F measured at location

Next month, we will continue with TMVs, hot water system startup and commissioning, and choosing the right temperature to set the maximum temperature limit-stops on shower and tub-shower valves.