8.3 Water Heaters, T&P & M.G.L. c. 142

8.3 Water Heaters, T&P & M.G.L. c. 142

Quick Answer: T&P in the top tapping (12 inches vertical / 6 inches horizontal, sensor within 5 inches), full-size unobstructed non-ferrous discharge to a fixture or within 12 inches of the floor, vacuum relief on the cold above the tank, no check valve on the cold inlet, pans under 6-gallon-and-up heaters over occupied space, ASME when over 120 gallons and/or 200,000 BTU outside a private residence or single condo unit.

The CIB gives heaters three items and then names M.G.L. c. 142 and Hot Water Tanks or Heaters. That is the statute sitting under 248 CMR 10.14(6). 248 CMR 10.14(6)(f) says safety devices on tanks, tankless heaters, and on-demand heaters shall comply with M.G.L. c. 142, § 19 and ANSI Z21.22. Tags on the jacket are c. 142, § 17. Working pressure for the stamp is c. 142, § 18E as applied by 10.14(6)(a). Read the code and the statute together; a question can cite either.

Occupied premises must supply hot water to fixtures used for bathing, washing, culinary work, cleansing, laundry, or building maintenance (10.14(5)(a)). Residential stored domestic hot water shall not exceed 130°F, with dishwashers and hot-water dispensers excepted. The 10.14(5) table is the rest of the temperature map:

If developed hot-water piping from the heater or recirculation loop to the farthest fixture exceeds 75 feet, the system is a total return circulation type; the recirculating line is at least ½ inch (10.14(2)(f)). That is the preview for the water chapter's recirc sizing.

M.G.L. c. 142 — tags, pressure, safety devices

Section 17 (statements by the manufacturer on range boilers and water heaters; certificates for cast-iron water fronts, heater elements, and hot water tanks) is the metal-tag statute. 248 CMR 10.14(6)(h) states that metal or foil tags permanently attached to most water heaters comply with M.G.L. c. 142, § 17. You do not field-stamp a second brass plate if the listed jacket tag is there.

Section 18 covers construction, installing, relocating, and repairing: capacity, strength, solder, and pressure. 10.14(6)(a) applies § 18E this way: working pressure of a hot-water tank is street or service pressure only, unless a booster raises house pressure above street pressure. Do not rate the tank from a hoped-for PRV setting downstream of a booster.

Section 19 is the safety-device statute. For a tank connected to a heating device that can deliver water greater than 212°F, Massachusetts requires a temperature relief valve in a tapping directly in or on the tank, within 12 inches of the top of a vertical tank or within 6 inches of the top of a horizontal tank, with no fittings between the valve and the tank except a bushing to reduce the tapping, or in the hot-water outlet as close to the top as possible. The heat-sensitive member shall not be more than 5 inches from the top of the tank. Discharge under § 19 is non-ferrous pipe or tubing not less than ⅜-inch inside diameter, with no shutoff, to an open plumbing fixture or to within 12 inches of the basement floor. 248 CMR 10.14(6)(f)2 repeats the location rule and tightens the discharge to full size of the valve outlet, non-ferrous or tubing rated for the valve's maximum temperature, no shutoff, to a fixture or within 12 inches of the floor. On the job, run full size (usually ¾-inch T&P outlet), which already exceeds the statute's ⅜-inch floor.

T&P relief and discharge piping

All storage water-heating equipment capable of heating water above 212°F gets a properly sized combination temperature-and-pressure relief valve. T&P valves must also meet the pressure-relief rating rules in 10.14(6)(f)1: on direct-fired heaters up to 200,000 BTU/h, the listed rating is not less than heater input; on-demand heaters likewise. Tankless heaters on low-pressure steam or hot-water boilers use Table 5 (½ inch up to 5 GPM, ¾ inch over 5 up to 20 GPM, 1 inch over 20 up to 50 GPM, 1–1¼ inch over 50 GPM under ASME). Heaters and storage tanks over 200,000 BTU need T&P valves that meet ASME and current ANSI Z21.22.

Discharge piping is where exams harvest easy misses. Current 248 CMR 10.14(6)(f)2.c plus M.G.L. c. 142, § 19:

Do not reduce, do not trap, do not hide the pipe in a closed sanitary fitting. If a replacement heater uses the 10.12(f) pan exception, the T&P shall discharge into the pan.

Vacuum relief, cold inlet, expansion preview

Tank-type heaters and storage tanks need vacuum relief on the cold-water supply at a level above the top of the heater or tank, with no shutoff between the vacuum relief valve and the tank (10.14(6)(f)3). Vacuum valves are at least one pipe size smaller than the tank drain. They may be installed in multiples per Table 6:

A check valve shall not be installed in the cold-water supply to any hot-water heater or storage tank. A properly sized thermal expansion tank may be installed to take the pressure rise. If the water meter already has a check or backflow preventer, 10.14(3)(j) requires a sized expansion tank close to that meter. Combination potable / space-heating systems must have a potable expansion tank (10.14(6)(g)4). That is the expansion preview: closed systems need a tank; a check on the heater cold inlet is the wrong way to "solve" expansion.

Each storage tank needs a drain valve at the lowest point. The heater cold-water shutoff is near the equipment and above the top of the tank. No coils, boosters, or other heating devices in direct contact with the heat-generating source of a building heating unit. Unattended basement storage connected to a direct heating appliance needs fully automatic control to keep water in any part of the tank from reaching 212°F.

Safe-waste pans — code and Board policy

248 CMR 10.12(f) (current 12.8.23 text) and the Board's Safe Waste Pans for Water Heaters and Storage Tanks policy (enacted November 28, 2011) now tell the same story:

1. Install a pan under water heaters, storage tanks, or boilers of 6 gallons or more that are elevated above any occupied space.
2. Pipe the pan indirectly to a properly trapped and vented fixture or to a point within 12 inches of the lowest floor level.
3. Minimum waste pipe 1 inch. Pan at least 2 inches deep with 2 inches of clearance around the appliance base. Discharge materials follow 10.06.
4. If a floor drain or other acceptable indirect point is already on the same floor level, no safe waste pan is required.
5. Replacement exception: when a pan and drain piping are not practical, install a product-accepted automatic water-heater shutoff and a pan without the related drain piping. The T&P shall discharge into that pan.

The 2011 Mass.gov policy is what first authorized that replacement alternate; the December 8, 2023 code folded it in as the 10.12(f) exception.

Combination potable water / space heating, ASME tanks, tags

248 CMR 10.14(6)(g) (and the Board's Combination Potable Water – Space Heating Systems policy, enacted May 30, 2012):

• Maximum 100 feet developed length from heater to fan coil and back (not counting the coil).
• Piping between heater and coil complies with 248 CMR 3.04 and 10.06. The Board diagram still shows minimum 2 feet developed length of Type L copper at the heater connections and an NSF-61 product-accepted pump.
• Electronically controlled pump timer operating at least once every 6 hours for a minimum of 60 seconds (keeps the potable loop from stagnating).
• Properly sized potable expansion tank.
• Mixing valve serving plumbing fixtures so outlet temperatures meet 248 CMR.
• T&P as required. A reverse-acting aquastat to shut the fan is suggested, not required, on the Board diagram.

ASME tanks — 10.14(6)(e) and the Board ASME Tank Requirements policy (enforced 2010, revised August 5, 2016):

Stamp as ASME when all of the following are true:

• Installed in other than a private residence or a single condominium unit where the heater serves only that unit, and
• Storage over 120 gallons and/or recovery equal to or greater than 200,000 BTU, and
• Direct or indirect fired (for indirect, use maximum output of the stored or transferred energy).

Private residence in the Board policy means a single-family dwelling only, or a single condominium unit with its own water-heating source. Code examples: an 80-gallon tank with 210,000 BTU recovery must meet ASME; two 100-gallon tanks fed by an indirect heater at 199,000 BTU shall meet ASME. An ASME data sheet signed by an authorized inspector goes to the owner/contractor, and a copy is permanently displayed on the wall adjacent to the water heater.

UL-174 alternate (in both the policy and 10.14(6)(e) exception): tank tested to two times maximum working pressure or 300 PSIG max, and to 150 PSIG / 210°F; minimum 10-year warranty; maximum four tanks in tandem.

Warranty-exchange tanks after the Board's long-expired 2003 grace period must meet the same ASME rule. Do not hang a non-ASME 150-gallon commercial tank because "it is a replacement."

Exam traps for 8.3

• T&P location is 12 inches (vertical) / 6 inches (horizontal) / 5 inches to the sensor — not 6 inches from the floor.
• Discharge is full size, non-ferrous, no shutoff, open end, fixture or 12 inches off the floor. Threading a cap on the outlet defeats the valve.
• Vacuum relief is on the cold, above the tank, with no shutoff between valve and tank. The heater isolation valve is still above the tank on the cold branch, but it cannot isolate the vacuum relief from the tank.
• No check valve on the heater cold inlet. Expansion tank is the closed-system answer.
• ASME is 120 gallons or 200,000 BTU outside a private residence / single condo unit serving only that unit. An 80-gallon 210,000 BTU commercial heater is ASME even though it is under 120 gallons.