Gunnar Alquist
11-11-2016, 11:42 AM
Hi folks,
I read a recent thread on another bulletin board regarding the requirements for expansion tanks, PRVs and TPRVs. The thread was in regard to changes in the 2015 UPC which will be incorporated into the 2016 CPC, specific to tankless/flash water heaters and apparently came from IAPMO, but I have not been able to verify this independently as I cannot get onto the IAPMO website. Below is the original post from the other BB and at the bottom are my thoughts. (Bold/underlining are mine)
2015 Guide to Important Code Changes
608.3 Expansion Tanks and Combination Temperature and Pressure-Relief Valves
What Changed
608.3 Expansion Tanks, and Combination, Temperature and Pressure-Relief Valves. A water system provided with a check valve, backflow preventer, or other normally closed device that prevents dissipation of building pressure back into the water main, independent of the type of water heater used, shall be provided with an approved, listed, and adequately sized expansion tank or other approved device having a similar function to control thermal expansion. Such expansion tank or other approved device shall be installed on the building side of the check valve, backflow preventer, or other device and shall be sized and installed in accordance with the manufacturer's installation instructions.
A water system containing storage water heating equipment shall be provided with an approved, listed, adequately sized combination temperature and pressure-relief valve, except for listed nonstorage instantaneous heaters having an inside diameter of not more than 3 inches (80 mm). Each such approved combination temperature and pressure relief-valve shall be installed on the water-heating device in an approved location based on its listing requirements and the manufacturer's installation instructions. Each such combination temperature and pressure relief-valve shall be provided with a drain in accordance with Section 608.5.
Why It Changed
There is a misunderstanding throughout the industry that, if a tankless water heater is installed, an expansion tank is not necessary; this is not true except for instantaneous heaters having an inside diameter of not more than 3-inches. These small units having practically no storage capacity do not have significant thermal expansion. Other than this exception, the above revision clarifies that, regardless of the type of water heater that is installed, thermal expansion can still occur in the cold water supply line. Therefore, an approved expansion tank or other approved device needs to be installed.
What It Means To Me
This language addition indicates to the installer and inspector that expansion tanks and Temperature and Pressure relieve valves must be installed on every type of water heater that is installed, except for instantaneous heaters having an inside diameter of not more than 3-inches. Otherwise, thermal expansion can occur when water is heated no matter the type of heater used.
These water heaters are protected in three stages. The primary stage is the thermostat.
Should the thermostat fail, the secondary stage or highlimit switch will turn off the source of energy to the heater. If the high-limit switch fails, the combination T&P valve opens to prevent a catastrophic failure of the water heater. Instantaneous water heaters having an inside diameter of three inches or less are exempt from having a T&P valve. These small units are without a storage reservoir, having only a heating coil that does not allow significant thermal expansion. When the need for hot water has been met the instantaneous water heater shuts off. It does not cause a great amount of expansion because there is not a large volume of water to heat or expand.
When installing a T&P valve it is critical that the installer check the rating plate on the combination T&P valve before installation to make sure that the Btu input rating of the water heater does not exceed the maximum Btu rating of the valve. The use of an undersized combination T&P valve could result in a catastrophic water heater failure should both the water heater thermostat and the water heater high-limit switch fail. In instances where there are two separate Btu ratings on the valve plate, the smaller of the two is used in making this determination.
Manufacturers of T&P valves require that the valve be installed with its temperature-sensing element immersed within the top 6 inches of the tank since this is where the hottest water in the tank is located. Manufacturers recommend that they be manually opened at least once a year to ensure that they are functioning. In areas that have a high mineral content in the water, scale can form around the valve seat and render the valve inoperable. In such areas, it may be necessary to manually open the valve every three months or less. A water heater is a potential bomb that is prevented from exploding by three separate safety devices. The combination T&P valve is a lifesaver and is treated accordingly.
So, I am having trouble with the explanations (Why It Changed and What It Means To Me) seem to contradict the code. The way I read the first paragraph of 608.3 is the requirement for expansion tanks is regardless of the type of water heater. The second paragraph address the requirement for PRVs on tankless/flash water heaters with an interior diameter of 3 inches or less and a requirement for TPRVs on tankless water heaters with an interior diameter of greater than 3 inches.
In addition, when I searched online for help, I found interpretations that I cannot reconcile to the code or the explanations in the above text.
See p. 3 item #16 on the link below:
http://www.seattle.gov/dpd/cs/groups/pan/@pan/documents/web_informational/p2357861.pdf
See p. 11 on the link below.
http://www.wabo.org/assets/AEI/2016Handouts/2015%20upc%20wa%20state.pdf
By the way, has ANYONE seen a tankless/flash water heater with an interior diameter of 3 inches? I assume they are referring to the diameter of the heat exchanger tubing...
I read a recent thread on another bulletin board regarding the requirements for expansion tanks, PRVs and TPRVs. The thread was in regard to changes in the 2015 UPC which will be incorporated into the 2016 CPC, specific to tankless/flash water heaters and apparently came from IAPMO, but I have not been able to verify this independently as I cannot get onto the IAPMO website. Below is the original post from the other BB and at the bottom are my thoughts. (Bold/underlining are mine)
2015 Guide to Important Code Changes
608.3 Expansion Tanks and Combination Temperature and Pressure-Relief Valves
What Changed
608.3 Expansion Tanks, and Combination, Temperature and Pressure-Relief Valves. A water system provided with a check valve, backflow preventer, or other normally closed device that prevents dissipation of building pressure back into the water main, independent of the type of water heater used, shall be provided with an approved, listed, and adequately sized expansion tank or other approved device having a similar function to control thermal expansion. Such expansion tank or other approved device shall be installed on the building side of the check valve, backflow preventer, or other device and shall be sized and installed in accordance with the manufacturer's installation instructions.
A water system containing storage water heating equipment shall be provided with an approved, listed, adequately sized combination temperature and pressure-relief valve, except for listed nonstorage instantaneous heaters having an inside diameter of not more than 3 inches (80 mm). Each such approved combination temperature and pressure relief-valve shall be installed on the water-heating device in an approved location based on its listing requirements and the manufacturer's installation instructions. Each such combination temperature and pressure relief-valve shall be provided with a drain in accordance with Section 608.5.
Why It Changed
There is a misunderstanding throughout the industry that, if a tankless water heater is installed, an expansion tank is not necessary; this is not true except for instantaneous heaters having an inside diameter of not more than 3-inches. These small units having practically no storage capacity do not have significant thermal expansion. Other than this exception, the above revision clarifies that, regardless of the type of water heater that is installed, thermal expansion can still occur in the cold water supply line. Therefore, an approved expansion tank or other approved device needs to be installed.
What It Means To Me
This language addition indicates to the installer and inspector that expansion tanks and Temperature and Pressure relieve valves must be installed on every type of water heater that is installed, except for instantaneous heaters having an inside diameter of not more than 3-inches. Otherwise, thermal expansion can occur when water is heated no matter the type of heater used.
These water heaters are protected in three stages. The primary stage is the thermostat.
Should the thermostat fail, the secondary stage or highlimit switch will turn off the source of energy to the heater. If the high-limit switch fails, the combination T&P valve opens to prevent a catastrophic failure of the water heater. Instantaneous water heaters having an inside diameter of three inches or less are exempt from having a T&P valve. These small units are without a storage reservoir, having only a heating coil that does not allow significant thermal expansion. When the need for hot water has been met the instantaneous water heater shuts off. It does not cause a great amount of expansion because there is not a large volume of water to heat or expand.
When installing a T&P valve it is critical that the installer check the rating plate on the combination T&P valve before installation to make sure that the Btu input rating of the water heater does not exceed the maximum Btu rating of the valve. The use of an undersized combination T&P valve could result in a catastrophic water heater failure should both the water heater thermostat and the water heater high-limit switch fail. In instances where there are two separate Btu ratings on the valve plate, the smaller of the two is used in making this determination.
Manufacturers of T&P valves require that the valve be installed with its temperature-sensing element immersed within the top 6 inches of the tank since this is where the hottest water in the tank is located. Manufacturers recommend that they be manually opened at least once a year to ensure that they are functioning. In areas that have a high mineral content in the water, scale can form around the valve seat and render the valve inoperable. In such areas, it may be necessary to manually open the valve every three months or less. A water heater is a potential bomb that is prevented from exploding by three separate safety devices. The combination T&P valve is a lifesaver and is treated accordingly.
So, I am having trouble with the explanations (Why It Changed and What It Means To Me) seem to contradict the code. The way I read the first paragraph of 608.3 is the requirement for expansion tanks is regardless of the type of water heater. The second paragraph address the requirement for PRVs on tankless/flash water heaters with an interior diameter of 3 inches or less and a requirement for TPRVs on tankless water heaters with an interior diameter of greater than 3 inches.
In addition, when I searched online for help, I found interpretations that I cannot reconcile to the code or the explanations in the above text.
See p. 3 item #16 on the link below:
http://www.seattle.gov/dpd/cs/groups/pan/@pan/documents/web_informational/p2357861.pdf
See p. 11 on the link below.
http://www.wabo.org/assets/AEI/2016Handouts/2015%20upc%20wa%20state.pdf
By the way, has ANYONE seen a tankless/flash water heater with an interior diameter of 3 inches? I assume they are referring to the diameter of the heat exchanger tubing...