Frequently Asked Questions
Q. "Does a hot water recirculating system use up a lot of energy?"
A. Both options use energy. But not as much as most people think. On the recirculating system we highly recommend insulating all of your hot water pipes. Also having a timer and/or a thermostat will use even less energy. An electric tankless water heater doesn't use any energy when you're not drawing hot water.
Q. "Is the thermostat adjustable?"
A. The thermostatic control automatically turns the circulator off when the temperature exceeds approximately 105°F and back on when the temperature drops below approximately 85°F. The thermostat is not adjustable. You can click here to read more info about the thermostat.
Q. "Your timer seems expensive. Is it necessary?"
A. Most three-prong wall timers should work, but Grundfos makes a fantastic timer for their most popular model (#UP15-18SU). It can be set in 15-minute increments, mounts right onto the pump, and is the best timer we have ever seen. You can click here to read more info about the timer.
Q. "On your cast iron pumps you say that they are only for a closed system. What is a 'closed system'?"
A. A closed system is a recirculation loop for water (or other liquid) where once it is set up and running, no new liquid is introduced into the system. If new liquid is brought into the system it will bring air with it and over time this will rust out a cast iron pump.
Q. "Why don't you recommend ordering thermostats with the line cord pumps?"
A. Due to these pumps being pre-wired, they would require re-wiring in order to use the thermostats, so we recommend you purchase the pump, thermostat and timer separately when you want to use a thermostat.
Q. "Why do I need flanges/unions?"
A. The threads on the pumps are designed to attach only to the flanges or unions. There are many different sizes and types of pipe. Using flanges/unions means they don't have to make a different pump for every different size & type of pipe.
Q. "I am purchasing a replacement Grundfos pump. Next to the pump it states: 'one set required.' Must I (am I required to) order flanges/unions along with the pump or can I just order the pump?"
A. If it is an identical replacement Grundfos pump you certainly don't need to purchase flanges/unions again. The ones that you currently have "should" fit fine.
Q. "How is the quality of a Grundfos brand pump?"
A. We know of no finer made pump. Having said that we do want you to realize that every pump has a specific function. Meaning, for example, a circulating cast iron pump isn't generally for domestic drinking water. Every pump also has a specific flow rate, etc. so please don't assume that you can simply order the lowest priced Grundfos pump and that it will work for your situation. Grundfos is top quality but recognize that a $20,000 bicycle might not go as fast as a $15,000 car.
Q. "On your flanges/unions, what does 'ISO' mean?"
A. The ISO (isolation) flanges have a screwdriver shut-off built into them so the pump can be removed from the system without turning off the water supply.
Q. "Which pump would you recommend for most residential recirculation systems?"
A. Our most popular unit is the #UP 15-29SU (formerly the #UP15-18SU). It's a very quiet unit and uses less electricity than most light bulbs (65 watts!). For even more savings you can also incorporate a timer and/or thermostat.
Q. "You offer/show such a great selection and since I need the pump right away am worried that it won't ship right after I order it. How's your inventory on these?"
A. Over 95% of the pumps are always in stock and ship within 24 hours of us receiving your order (Mon-Fri).
Q. "What is the benefit of installing an optional timer or thermostat?"
A. Either one will save energy (and money). The timer only allows the pump to turn on at certain times. So if you only need hot water in the morning, you could set the timer for 6am to 8am. Then the pump would only recirculate the hot water during that time. The thermostat turns off the pump when the water in the pipes reaches a certain temperature. So once the water in the pipe is hot, the pump turns off. When the timer and thermostatic controls are installed together, in series, the circulator operates ONLY at the preset clock times specified by the user AND ONLY when the temperature conditions of the thermostat are met. That is, if either the timer control or the thermostatic control switch is open (off), the circulator will not operate.
Q. "What else would I need to install a hot water recirculation system?"
A. You'll need the pump and flanges/unions of course; a swing check valve, and pipe and pipe fittings to run the return line back to the pump. A timer and/or thermostat are optional. (click here for instructions and more info on these).
Q. "Are the Grundfos stainless steel pumps specified for potable hot water?"
A. Absolutely. They are an excellent choice for drinking water.
Q. "I want to install a hot water circulation loop so that I can get hot water quickly at my taps. My problem is that I have to pump it up about 20 feet and I only have 40 psi. Will a 1/2" return line work ok?"
A. You could even use 3/8" on the return line (after the last fixture). Best to go with 1/2" but there is no reason to use 3/4" pipe. When your system is entirely under pressure, while the Grundfos pump is "pushing" up, the water is also "dropping" down. Just make sure to get rid of ALL of air in your return line and design your system so that no air will be in your line.
Typical hot water system before a recirculation pump.
Common recirculation pump installation.
Close-Up of pump installation.
Notes on installation:
Now that you're going to have hot water in your pipes all the time we strongly recommend insulating your hot water pipes as well as the return line to avoid stand-by heat loss.
A 2" clearance should be kept between the hot and cold water lines.
Branches off of the main hot water supply should be kept as short as possible.
Local codes may require the installation of a hot water expansion tank for secondary pressure relief on cold water supply lines with check valves.
The pump should be installed with the motor shaft horizontal.
It is very important that there is no trapped air in the pipe or the pump. Unless you have extremely oversized the pump (which wastes a lot of energy), trapped air in the return line can damage the recirculation pump. With these Grundfos recirculating pumps, air removal from the pump can be accomplished by releasing air from the chrome slotted plug located on the front of the pump. IMPORTANT: This chrome plug must NOT be removed. This chrome slotted plug is to release air from the pump only, not from the entire circulation piping system. After the system is charged with water make sure the power to the pump is turned off. Position a bucket under the pump because water will begin to stream from the plug as the air is released. Slowly unscrew the chrome slotted plug counter clockwise, until small bubbles of air and water appear. As soon as tiny bubbles or water appear, stop unscrewing the chrome plug any further. Allow all the air to escape. When only water streams slowly out of the pump then you will know the air has been purged. Tighten the chrome slotted plug clockwise. To prevent air from collecting in the return line, slope all the pipes so air will flow to the high point in the return line and then put an air vent there so you can release the air periodically.
The return line can be installed either under the floor or in the ceiling.