October 18, 2021

Professional Tool Reviews for Pros

Installing the Watts Hot Water Recirculating Pump 500-800

Do you have to run your faucet in the morning for a few minutes before you get hot water? Those days can be over with the low cost and simple install of the Watts 500800 Hot Water Recirculation System. This system is well suited for existing homes where it is nearly impossible to run a new hot water recirculation pipe.

Watts 500800 Hot Water Recirculation System water heater

Do you have to run your faucet in the morning for a few minutes before you get hot water? Those days can be over with the low cost and simple install of the Watts Hot Water Recirculating Pump (model 500-800). This system is well suited for existing homes where it is nearly impossible to run a new hot water recirculation pipe.

We chose this system to be installed in a beach house where they had over 100 feet of piping from the water heater which was located in a small mechanical room below the house to the master bathroom sink faucet on the other side of the house on the second level. To further complicate the plumbing situation at this home, all the main supply piping from the water heater was run under ground, then up the side of a 10 ft high wood pier into the home above. Since there is no way to insulate the piping beneath the concrete slab under the home, there was a tremendous amount of heat loss. This is especially evident after the hot water sat in the pipe over night. In the morning it would take a least 4 minuets before the water would come out warm from the faucet. We figured this house would be an extreme example of this type of scenario and a great application of a product like the Watts 500800 Hot Water Recirculation System.

Watts Hot Water Recirculating Pump 500-800 Installation

The pump appears to be well made with heavy solid brass pump housing. The pump controls and timer is integrated into the pump assembly. Also included in the box were the bypass valve, two flexible stainless steel sink connection hoses with adapters and the instruction book. For all the various types of plumbing systems out there, you will have to match up your pipe type with a threaded coupler to mate with the pump; these additional fittings were not included in the box.

Watts 500800 Hot Water Recirculation System

We gave the Watts Hot Water Recirculating Pump instruction book a quick read, just to make sure we had all the parts and we understood the concept of the system. For our installation we started at the water heater. We had just swapped out water heater so we had the water heater and piping already drained and ready for the modifications necessary to pipe the pump. The pump is supposed to be installed on the hot water out side of the water heater. For this install we opted to use some dielectric unions between the hot water heater connection and our copper piping. The dielectric union servers two purposes, one is to minimize the corrosion that often happens when dissimilar metals come in contact with each other and the second benefit of using them is it makes it easy to disassemble the piping from the water heater should that be necessary in the future. Since our installation involved sweated copper joints, I proceeded to make the proper connections so that the threaded ends of the pump connections would work with the plumbing. The installation of the pump was very straightforward and the directions were easy to follow. For power to the pump. we plugged it into a nearby GFCI protected receptacle via the 10 foot long power cord that came attached to the pump.

The second part to the system is a small plastic bypass valve that gets installed under the sink that is the farthest away from the hot water heater. First I shut off the water at the valves under the sink. Next I disconnected the supply lines from the valves. I used a single screw to secure the new bypass valve to the wall in between the hot and cold water valves. Then I proceeded to connect up the piping to the correct points on the valve. There are two sets of connections that were clearly labeled. One set feeds the faucet and one set is where the water supply comes into the valve. The included flexible water lines are designed to connect the bypass valve to the water supply valves. Once all the connections were tight we were finished here.

Watts 500800 Hot Water Recirculation System install

Now came the moment of truth. Well actually we had to wait for a good couple of hours for the moment of truth. It takes a while for a new water heater to fill up, then to heat up the water and then to have that hot water distributed though the system. Once all the air was bled out of the system and water was flowing, we checked for leaks one last time and packed up our tools and went home. The next morning we called the homeowner to see how the water felt first thing in the morning and he said that it only had to run for a few second before it was hot. This was a significant improvement because most of the time it would need to run for almost 5 minutes for the same effect.

How Does It Work

At this point you are probably wondering how the system works. The key to the Watts 500-800 Hot Water Recirculation System is in the bypass valve we installed under the sink. As the circulatory pump on the water heater pumps hot water into the line, the bypass valve opens and closed automatically based on the water temperate at in the pipe at the sink. When the hot water reaches 98 degrees (+/- 5 degrees F) the valve closes, when the temperature falls below this, the valve opens and a small amount of the hot water then circulates into the cold water supply line until the hot water temperature is again brought up to the correct temp. By keeping even a small amount of the hot water flowing back though the system in the cold water line, it ensures that there is always hot water available. It is interesting to note that the cold water at the sink was not as cold as it was before the install because of the small amount of hot water be introduced into it. The cold water never gets warm though and just seconds after turning on the cold water, it is flowing nice and cold. The controller on the pump has several settings, one is that you can leave the pump on all the time, another setting is to use the timer to have the pump only run at certain times of the day when you know you normally expect hot water like in the mornings or evenings.


Having been a skeptic at first, I will have to say I was sold by the low cost ($239 MSRP but can be found for less online), high quality and easy of application. The Watts Hot Water Recirculating Pump 500-800 can be used for nearly any house where you have to wait for the water to get hot at a distant faucet. To do a quick check of the potential cost savings we will take an average home with 125 feet of 3/4 inch pipe. 125 feet of 3/4″ copper pipe holds 3.14 gallons of water. With 10 draws per day, that will waste almost 31 gallons of water if the water runs for one minute while you wait for it to get hot. Over a year, that equals 11,461 gallons. The system is not recommended for tankless or instant water heater type systems since those types of systems are based on different methods to heat the water.

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So i bought this unit for my outdoor tankless water heater. Unfortunately the directions state that it is for indoor use only and I’m trying to do this myself without having to cut any pipe. Can this be installed under the sink in between the hot water line and sensor valve?

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