Hot Water Now
Recirculation systems eliminate a long wait at the tap and save thousands of gallons of water.
Synopsis: If your morning routine includes a walk to the bathroom to turn on the shower before heading to the kitchen to make breakfast while you wait for the shower water to get hot, you’re not alone. Most conventionally plumbed houses have lethargic hot-water delivery systems that waste your time, your water, and your money. The good news is that the solution is simple for new houses or old. Hot-water recirculation is not new technology; it has been used for decades in commercial buildings. The concept is easy to understand: Hot water circulates through the plumbing so that it is there when you need it. The details, however, are a little more complicated. In this article, contributing editor Scott Gibson explains the basics of hot-water recirculation for new and existing homes and discusses some of the details that make some systems more convenient and energy-efficient than others.
It takes about 90 seconds for hot water to reach the shower in my bathroom. As I wait, a lot of water goes down the drain.
This waste can add up to thousands of gallons of water each year—and a lot of money— which makes a good case for a plumbing alternative known as hot-water recirculation.
When properly designed and used, hot-water recirculation systems add only marginally to construction costs. They are inexpensive to operate; they virtually eliminate wasted water; and they provide instant hot water. A recirculation system can be added to an existing house pretty easily, too.
Although point-of-use water heaters are another option for bringing hot water to the tap faster, recirculation systems are a far more practical, whole-house solution.
Recirculation reduces waste and wait
In conventionally plumbed houses, water is piped through trunk and branch lines. Trunk lines, usually 3 ⁄4-in. pipe, carry water to areas in the house where it is needed. Branch lines, usually 1 ⁄2-in. pipe, extend from the trunk lines to individual fixtures and appliances.
The problem is that when hot water is not being used, it rests in the lines and cools. Then, when hot water is needed, the cool water that was resting in the hot-water lines flows down the drain, wasting water while you wait for hot water to reach the tap.
A few different types of recirculation systems can solve this problem. Common to most of them is an electric pump that circulates hot water through a combination trunk/return line that carries unused hot water back to the water heater. Circulating through the trunk line, hot water is only as far away as the branch line is long, minimizing both the waste and the wait.
Where hot-water recirculation systems differ is in the details. The pumps can run continuously; only when timer and/or thermostat settings permit (with time-and-temperature systems); or when activated manually (with on-demand systems).
Efficiency varies with each system
The simplest recirculation system consists of a small, continuously operating pump. Hot water circulates slowly (low-flow pumps circulate as little as 2 ⁄10 gal. per minute) through the trunk lines and returns to the water heater if unused.
A low-volume pump may require as little as 25 watts of electricity. However, the trunk lines effectively become an extension of the water heater, and heat loss can be significant.
To make the system more efficient, a timer can be used to control when hot water is pumped around the loop. If hot water is needed mainly between 6:30 a.m. and 8 a.m., then the timer can be set to run the pump only during those hours. A thermostat, or more accurately, an adjustable aquastat that monitors water temperature and turns the pump on and off, further reduces operating costs. Hot water flows only when both time and temperature settings are right. Time-and-temperature pumps including an aquastat cost less than $300.
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