TPRV on Tankless Water Heaters

[Mike Birenbaum]

I need help clarifying and/or identifying the TPRV on a tankless water heater. I have seen more and more tankless installations lately and when double checking and reading the MFG. label for installation guidelines, I have seen a paragraph depicting TPRV requirements (on the mfg. label), but am unable to visually idenitify what I know to be a TPRV valve and assembly. Attached are photos of a recent assembly including the "paragraph" on the label....Any help is always greatly appreciated.

[Ron Hasil]

What is installed on the bottom of that heater is service valves. The T&P valve should be installed on the hot side of that service valve. In the pictures I do not see one installed, it looks to me the port for the T&P valve has a plug in it.

It used to be the manufactures only required a Pressure relief valve, as time goes on they now realize most plumbing codes require a temperature and pressure relief valve. Here in Illinois there is more requirements on the install of a tankless water heater and the new hybrid water heaters (has a storage tank built in like Navien and Eternal) require Thermostatic mixing valve installed, a pressure relief valve installed on the cold water supply, and a T&P valve installed on the tempered line.


TITLE 77: PUBLIC HEALTH
CHAPTER I: DEPARTMENT OF PUBLIC HEALTH
PART 890 ILLINOIS PLUMBING CODE

SECTION 890.1220 HOT WATER SUPPLY AND DISTRIBUTION

7) Indirect, External, Submerged Coils. Indirect, external, tankless or submerged coils used in heating water shall be equipped with a thermostatic mixing valve or valves when not connected to a storage tank. A pressure relief valve shall be installed on the cold water inlet of the tank. A properly sized temperature and pressure relief valve, based upon the energy input rating of the coils, shall be installed on the tempered line with the temperature sensing element immersed in the tempered water line as close as possible to the mixing valve.





8) Direct Fired Instantaneous Heaters. (Storage tank of more than 64 fluid ounces.) Direct fired instantaneous water heaters shall be equipped with a thermostatic mixing valve or valves which conform to ASSE 1017-1999. A pressure relief valve shall be installed on or adjacent to the heater. A properly sized temperature and pressure relief valve, based upon the energy input rating of the heater, shall be installed on the tempered line with the temperature sensing element immersed in the tempered water line as close as possible to the mixing valve.

[Jerry Peck]

What I've found strange is that if that water heater is installed in an apartment (which is a dwelling unit), a condo (which is a dwelling unit) in a structure which is built under the IPC instead of under the IRC (same applies to the Florida codes, which is where I first noticed it) then a vacuum relief valve is required, yet ...

... if that same exact water heater is installed in a dwelling unit which is constructed under the IRC, then a vacuum relief valve is NOT required ... ???

Both would be the exact same water heaters, both would be installed as bottom fed, yet the IRC does not require the vacuum relief valve.

Can anyone explain why it would be required in one dwelling unit and not in another dwelling unit? :confused:

[Ron Hasil]

What I've found strange is that if that water heater is installed in an apartment (which is a dwelling unit), a condo (which is a dwelling unit) in a structure which is built under the IPC instead of under the IRC (same applies to the Florida codes, which is where I first noticed it) then a vacuum relief valve is required, yet ...

... if that same exact water heater is installed in a dwelling unit which is constructed under the IRC, then a vacuum relief valve is NOT required ... ???

Both would be the exact same water heaters, both would be installed as bottom fed, yet the IRC does not require the vacuum relief valve.

Can anyone explain why it would be required in one dwelling unit and not in another dwelling unit? :confused:

Ah glad you brought that up Jerry. They are required here in Illinois as well. Its in the next section of our plumbing code.


TITLE 77: PUBLIC HEALTH
CHAPTER I: DEPARTMENT OF PUBLIC HEALTH
SUBCHAPTER r: WATER AND SEWAGE
PART 890 ILLINOIS PLUMBING CODE
SECTION 890.1230 SAFETY DEVICES


f) Vacuum Relief Valve. Where a hot water storage tank or water heater is located at an elevation above the fixture outlets in the hot water system, or if the storage tank or water heater is bottom fed, a vacuum relief valve as listed in Appendix A, Table A (Approved Standards for Plumbing Appliances/Appurtenances/Devices) shall be installed on the storage tank or heater.

[Steven Turetsky]

Mike,

I've attached a photo of a TPR valve on a tankless water heater. It is on the bottom left. This installation is not yet complete; the drain tube is not present.

[H.G. Watson, Sr.]

Attached is the spec page (pdf - one page) for the pictured older model (webstone) Isolator E-X-P tankless water heater service valves I believe you have pictured below the tankless unit. Newer isolation service valves have the drain valve handles color coded red & blue. An even newer space saving model incorporates the thread port for the PRV above the valve assemblies between same and the tankless unit.

You can see the location on the hot valve (left) where the PRV is to have been mounted (and then its subsequent discharge pointing down). It MUST be prior to any isolation valve (and unencumbered) on the hot line.

When isolation servicing valves aren't used you'll often find elsewhere on the hot water line. Some manufacturers incorporate upon a manifold.

When the unit is an outdoors type prevention of freezing is also of issue.

P.S. concerned about the splice,bundling & exterior routing of non-OEM non-specified cable for the remote control unit, and the non-specified method and altered power cord installation to the unit (no UL "knot" inside, and grounded on guard outside the unit wrapped around sheet metal screw). Presence of (upright?) vacuum cleaner handle in alcove or closet indicates inappropriate storage in area and clearance required to remain clear (26 or so inches in front of unit). Damage to poorly installed and potentially inappropriate type pipe insulation further suggestive of inappropriate storage and questionable protection of plumbing systems (potable cold, hot, and gas (including appliance connector).

[Ron Hasil]

One other note, the flexable gas supply is wrong. The manufactures prefer it to be hard piped with 3/4", or if they use CSST gas piping it has to be 1"