A thermostatic mixing valve (TMV) can be used to regulate the temperature at plumbing fixtures to prevent hot water scald potential. The mixing valve will reduce the point-of-use water temperature by mixing the hot water from the water heater with a cold water supply. This allows the user to safely increase the tank water temperature setting above 125°F, which will increase the thermal storage capacity of the domestic hot water system. Heating tanks to 140°F significantly reduces legionella risk.
Installing a Heat Pump Water Heater is similar to installing an electric resistance water heater, so additional trades are typically not needed. Installation is usually simple, with no refrigerant handling required. In addition to following the guidance of product manuals, consider the following best practices:
This is Part III of an expert best practices web guide to Heat Pump Water Heaters published by the ENERGY STAR Residential New Construction program. Read Part I of the guide .
Increasing the temperature of the tank from 125°F to 140°F adds an equivalent amount of available hot water as increasing tank capacity by about 10 to 15 gallons.
Thermostatic mixing valve near a Heat Pump Water Heater. Credit: New Buildings Institute
A TMV also allows for optimization between when the water heater uses electricity from the grid to heat the hot water versus when the occupants demand hot water. The Heat Pump Water Heater can heat extra stored hot water when electricity rates are low, preventing the need to heat the water when electricity prices are high. Peak hot water demand often corresponds to periods of peak electric grid demand; TMVs allow occupants to better take advantage of utility load-management programs or time-of-use electric rates, managing electric demand and electricity costs.
Although TMVs are typically installed as a separate component, some manufacturers integrate them into their water heaters. Install a thermostatic mixing valve in the hot water supply line if the unit doesn&#;t come with an integrated mixing valve.
Install flex piping to the cold-water inlet and hot-water outlet connections to reduce vibrations from the Heat Pump Water Heater. Flex piping is also recommended when the Heat Pump Water Heater is in a confined space and the piping must bend.
If the water heater lacks pre-installed check valves, install a check valve or heat trap on both the cold water inlet and hot water outlet piping as close to the tank as possible to reduce heat loss from natural convection. Flex piping can be used to create a U-shaped or loop-shaped heat trap. Check the manufacturer specifications or installation instructions for heat trap type installation recommendations and confirm if the water heater comes with pre-installed check valves.
Some Heat Pump Water Heaters are equipped with built-in leak detection at the bottom of the tank and automatic shut-off controls. Regardless of whether the Heat Pump Water Heater is equipped with automatic leak detection, it is a best practice to install a drain pan to mitigate potential problems from leaks, especially if installed on a floor susceptible to water damage. Connect the outlet from the pan to a suitable drainage line and pitch for proper drainage.
Electric storage water heaters, including Heat Pump Water Heaters, do not need to be raised off the floor with a stand; this was a safety provision for older atmospheric gas storage water heaters.
Image credit: Northwest Energy Efficiency Alliance
Insulate hot water piping to at least the minimum requirements in IECC R403.5.3 or in accordance with local codes&#;whichever is greater. To improve overall system performance, insulate all hot water piping. It is more important to make sure the pipe insulation is continuous than it is to increase the wall thickness or R-value of the pipe insulation.
Most Heat Pump Water Heaters have internally insulated tanks and do not require blanket insulation. The manufacturer&#;s warranty may not cover damage or defects caused by installing blanket insulation.
The temperature and pressure relief (TPR) valve should be installed per the manufacturer&#;s recommendations. It is a best practice to install the discharge line to the outlet of the TPR valve and terminate the discharge line within 6 inches of a floor drain to prevent discharge water from contacting people or electrical parts.
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If pipe runs to fixtures are too long, use an on-demand, motion sensor, or occupant-activated pump to circulate just enough water to prime the loop with hot water Connect the return pipe of the circulation loop to the cold inlet of the water heater; this will guide the cooler returning water to pool at the bottom of the tank so it does not interfere with hot water availability.
Do not use a continuously operated circulation pump. Continuous circulation is particularly detrimental to heat pump water heaters as it may force the unit into &#;Electric Only&#; mode, which will result in a lack of hot water availability and greatly increase energy use. Consequently, never set the circulation system controls to continuous, and advise the homeowner or occupant of this requirement.
Check local codes to confirm if seismic strapping is required. Areas with medium to high levels of seismic activity require the water heater to be strapped with at least two 22-gauge straps. Refer to the product manual to ensure the straps are placed at the correct heights. Use rubber standoffs when attaching straps to the wall to minimize the vibration and transfer of sound to surrounding areas.
There are four basic operating modes on most Heat Pump Water Heaters: Economy, Heat Pump Only, Resistance Only, and Vacation. Some manufacturers may offer additional operating modes or use different names.
The default for most Heat Pump Water Heaters is hybrid operation mode where the heat pump is prioritized, but the unit may also use standard electric resistance during periods of high hot water demand. However, a properly-sized HPWH system can meet typical hot water demand without triggering electric resistance.
Operating the Heat Pump Water Heater in &#;Heat Pump Only&#; mode prevents the system from switching over to electric resistance, thus maximizing energy and cost savings. If the user has a temporary increase in hot water use&#;such as when there are house guests&#;and runs low on hot water, they can use &#;Hybrid Mode.&#; If the user is running out of water in &#;Heat Pump Only&#; mode, they should consider adding a TMV for additional thermal storage capacity.
Controls located directly on the HPWH or those accessible remotely from a or computer make it easy to switch options during times of high water demand. Consult the manufacturer manual.
Checking an air filter. Credit Northwest Energy Efficiency Alliance
Like any other water heater, Heat Pump Water Heaters require modest servicing. Common routine maintenance requirements specific to Heat Pump Water Heaters include cleaning the air filter and condensate lines. Air filters must be cleaned every 6 to 12 months, with a more frequent cleaning cadence in high-dust locations. Some units may provide automatic alerts when the filter needs cleaning. Condensate lines must be cleaned every year to make sure the condensate flows freely. Standing water in a lower metal drain pan may indicate a clogged condensate drain pan or lines.
Be sure to refer to the manufacturer&#;s operation and maintenance manual for specific guidance on the required maintenance and step-by-step instructions for the installed unit. Most current Heat Pump Water Heaters come in either 6- or 10-year limited equipment warranties.
Drawing of a split Heat Pump Water Heater. Credit Northwest Energy Efficiency Alliance
Split systems are heat pump water heaters in two parts, with the air-to-refrigerant heat exchanger commonly designed to be located outside. With the heat pump outside and the tank inside or in a garage, the two components are then connected with piping.
Split systems offer several advantages, including:
Preferred locations for hot water units are sometimes decisions made for us by rules and regulations. However, there are some locations that we would NOT recommend. As previously discussed, ceiling spaces are certainly undesirable places for hot water units due to the limited access and inability of the homeowner to see the unit and pick up any issues early. Under houses, where the height is restricted or access into the area is tight would also fall into the category for similar reasons to ceilings. Swimming pool plant rooms which would expose the system to chemicals such as chlorine and areas with no or difficult access to drainage would also not be recommended. The Ideal location can sometimes be difficult to achieve. But, ticking as many boxes as possible can make a big difference. Meeting all the relevant standards and being as close to the main point of use, coupled with the correct choice of system (link to the replacing hot water system blog) will see your new hot water unit performing as efficiently as possible.
When considering the ideal location to install a hot water system, several important factors should be considered to ensure efficient performance and compliance with regulations. Many of these will be determined by the original design of the property and plumbing systems. Ideally, the location of the hot water unit should consider the distance from the taps, access for maintenance, the risk of water escape and any relevant regulations. By considering all these factors, a hot water unit can be installed in the most efficient and appropriate location possible. We recommend consulting a hot water specialist, hydraulics engineer or builder to ensure the location is suitable.
For more information, please visit All in One Heat Pump Hot Water.