In a perfect world, one thing you should not have to wait for is hot water. Are you tired of turning the kitchen water on for several minutes before you can get warm water for washing pots and pans? What about the wait standing naked and shivering by the shower while cold water flows? How much water is wasted while your family waits for hot water? There are a variety of ways to have instant hot water in your home, and several solutions accomplish this goal without extensive retrofitting or unreasonable cost. For homeowners living in colder areas where the pipes can freeze, the hot water recirculating setup provides an additional benefit in preventing pipes from freezing. In this article, we will describe the problem that causes the wait for hot water and the various methods of solving the problem. One of those solutions may bring you closer to your perfect world.
The Problem
Here is the problem: cold water in the plumbing pipes of your home must be flushed before the heated water from the hot water heater can get to the fixture (the faucet or the shower) where the hot water is needed. Whether you have a tankless hot water system or a traditional hot water heater, to the extent there is water in a pipe between the sink or shower head, that water, which will be at ambient temperature, will have to clear before the hot water comes out at the fixture.
Point-of-use Solution
One way to solve the problem is to have a point-of-use water heater. Typically the point-of-use unit is a smaller tank, or a tankless unit rated for the use, located at the fixture. This provides nearly instant hot water because the water heater is located at the fixture and the hot water is in the pipe right at the fixture. However, the point-of-use solution does not solve the problem for other fixtures in the house.
Dedicated Hot Water Line Solution
Another way to solve the problem is to have the hot water circulation be in a loop so that the hot water is always circulating in the hot water line. This requires a home that is plumbed for a dedicated loop of hot water. Unless a house is already plumbed for a dedicated loop for hot water, it will be difficult and expensive to install the required plumbing line. If you are building a home, a dedicated loop for hot water could be plumbed in during construction of the home. This is the simplest installation because the circulating pump is installed in the hot water line and keeps hot water constantly in the line.
Retrofit Solutions
Other solutions to the hot water problem can be retrofitted into a home at a reasonable cost. A typical installation involves installing a circulating pump at the water heater. A thermal bypass valve is located by the fixture farthest away from the water heater and is attached to the hot and cold water lines. The thermal bypass valve uses a sensor, the pump at the water heater, and a valve to create a pressure differential in the hot water line. The pressure differential allows the cool water in the hot water supply line to bypass into the cold water supply line at a low volume through the thermostatically controlled sensor valve, keeping the water in the hot water supply line at a warm temperature throughout the home. Until water is a certain temperature the cool water in the pipe is recirculated back to the water heater and hot water from the heater is brought to the fixture. The sensor will stop the flow when the water in the hot water line reaches a certain temperature. Many of the pumps have timers to control operation periods so that the pump is not running during times no one is home or water use is low. One disadvantage to the use of the cold water pipe to circulate water back to the water heater is that when you want cold water, you will have to flush the hot water in the cold water line. Fortunately, this takes much less time than waiting for hot water where there is no circulating pump.
Installation
Let us focus on the installation of a typical hot water recirculation system for use with a tank water heater. This system involves a recirculating pump installed at the hot water heater and a thermal bypass valve unit installed under a sink.
The hot water heater can be a gas or electric heater. The pump unit mounts on the top of the hot water heater and requires a ground-fault 120-volt ac outlet. The first step in installing the pump on the hot water heater is to close the supply water valve to the water heater. The water is drained from the hot water pipes by opening a hot water faucet in the house. Drain the remaining water from the hot water heater spigot by draining the tank down a bit. Disconnect the hot water heater at the hot water heater discharge and install the pump so that the pump is pumping toward the house from the hot water heater. Connect the hot water line to the discharge connection of the pump. These connections are ¾” fittings. Depending on the hot water heater fittings there may be a need for a conversion connection. Reopen the supply valve to the hot water heater and allow the hot water to run until the air is purged from the pipes. Then the faucet inside the house can be closed. The electrical connection for the pump will require a ground-fault 120-volt ac outlet. Once plugged in the pump can be tested. Do not cause the pump to run without a flow of water.
Next the thermal bypass valve unit is located at a sink fixture the greatest distance from the hot water heater. The unit has connectors that run between the hot and cold water lines at the sink. At the sink, close both the hot and cold water stop valves below the sink. Disconnect the supply line connections from the hot and cold stop valves. The disconnected ends are connected to the adapter at the appropriate hot water and cold water connections. The unit usually comes with ½“ fittings. There may be a need to convert certain connections. Then install new lines from the unit to the appropriate hot and cold water stop valves. The thermal bypass valve unit will require access to a 120-volt AC outlet.
Another Retrofit Setup
Utilizing a low-voltage pump at the sink farthest from the hot water heater, another setup of a hot water circulation system that can be retrofitted into a home at a reasonable cost does not involve a pump installation at the hot water heater. This pump requires a 120-volt ac outlet and uses a transformer to provide 24-volt DC power to the pump. The pump has a built-in thermostat and performs the pump and thermal bypass valve function from one unit. That unit is connected in between the hot and cold water stop valves and the sink fixture similar to the way the thermal bypass valve unit was connected where the pump is located at the water heater. This type of unit can utilize a timer, but often the thermostat operation in the pump can be adjusted for constant operation, decreased temperature when water has not been used, and manual operation. The benefit of this type of installation is that installation is only under a sink and likely to be a less difficult installation.
One of the concerns with this setup is that the pump will take up more space under the sink than an thermal bypass valve unit. Even though the pump is a low voltage pump and not noisy in operation, noise from the pump still will be heard as opposed to the installation where the pump is located away from bathrooms and bedrooms. Because the unit is a single unit, the failure of the thermostat will require replacement of the whole unit, including the pump. This type of pump will not be as powerful such that where there are longer plumbing lines, more than one unit may need to be installed.
Tankless Hot Water Heater Installation
Pumps designed for tankless installation are installed similarly but average a slightly high price and usually require a higher capacity pump. Some tankless units come with circulating pumps, and, even if there is no hot water circulation line plumbed in, the pump can still be used with the appropriate thermal bypass valve unit. If the tankless unit does not have a circulating pump, a circulating pump and thermal bypass valve unit can be added much as with a tank water heater, but with different pump and flow requirements.
Cost–Benefit Analysis
Let us examine the economics of a hot water recirculating pump setup. Expect to pay anywhere from $200 to $500 for a pump and thermal bypass valve unit. For the purposes of this exercise, we will use the general maximum flow rate for faucets of 2.2 gallons per minute (on average, faucet flow will be a little less, and shower flow will be a little more). Assume an average wait of 3 minutes, that is 6.6 gallons for every instance of waiting for hot water. If that is done 4 times a day, there is waste in excess of 79 gallons a day. At the average price for water in the United States of $1.50 for 1,000 gallons, the daily cost of water down the drain is about twelve cents a day. That is an annual cost of about $43. This suggests that the cost of the setup, ignoring time or labor, is repaid in water savings after about five to six years. Obviously, the more the water use and the higher the cost of water, the more the savings will be.
Troubleshooting
Troubleshooting the pump operation and the circulation system is fairly straightforward. The pump is not a high-pressure pump and should not make excessive noise. Where pump operation is noisy or halted, the problem is often air in the plumbing line. As with any pump, there can be an airlock. Therefore, it is important to purge the air from the pipes anytime the lines are opened. Corrosion can occur with any water pipe, but it is more likely to happen in a hot water pipe. Any debris or particle matter in the water pipes could prove to be a problem for a recirculating pump. In some installations, it may be necessary to install a filter before the pump.
Considering the Options
Keep these options in mind when selecting a circulating pump system:
• If the installation is new construction, plumb dedicated hot water return lines.
• Where will the pump be installed? At the water heater or at the farthest sink? What will be the tolerance for noise at the pump location? If the pump is located at the water heater, is there a dedicated ground-fault 120-volt AC outlet available?
• At the sink farthest from the hot water heater, is there a 120-volt AC outlet available?
• Will you use a thermal bypass valve unit at the sink farthest from the water heater? Is there a need for conversion connections to the hot and cold water lines?
• What are the connections to the water heater? What is involved with making the proper connection to the pump unit through the hot water discharge line from the water heater? Are converter connections available for the lines to the water heater?
• Does the system use a timer, thermostat, or both? Some systems offer both a thermostat adjustment and a timer. A timer is better where the household has a regular schedule. While the thermostat can handle demands for hot water at different times, it will cause the pump to operate more often.
•Is there an issue with particulate matter or sediment in the water? If so, the operation of the circulation pump could be adversely affected. There may be a need to install a filter into the system.
Perhaps you cannot live in a perfect world, but you can have instant hot water. No more shivering waiting for the shower. The pots and pans in the kitchen can be rinsed and washed immediately. Even if you do not have a hot water circulating line plumbed into your home, you can still retrofit a hot water circulation system for a reasonable cost. The savings on wasted water can pay for the cost of the pump and thermal bypass valve unit within five years. One of these described installations will provide instant hot water in your home.
