Gravity Hot Water Recirculating Loops
Summary: Hot water needed now? Hot water
recirculating systems work best with a gravity loop.
Related Articles: Water Heater Recirculating Pumps Video, Hot Water Recirculating Loop, Hot Water Recirculating System - Installation Tips, Hot Water Recirculating System, Retro-Fit Recirculating Pump Comparison
DEAR H.O.: Brrrrrr! I know the feeling. Cold showers are a bummer. Guess what? We can solve your problem with a simple gravity hot water recirculating loop. They are effective, inexpensive and easy to install.
First, however, I want to put into perspective the waste situation. Clean water is a natural resource and should not be wasted. Until your loop is operational, why not capture the shower water with a bucket? Use it to water plants or to fill your washing machine. The cost of the wasted water is minuscule. Let's assume you pay only 1.5 cents for each cubic foot of water (that is my rate).
If you have 25 feet of 3/4 inch water pipe between your hot water heater and the shower, you waste .076 cubic feet of water each morning or $0.001178. It would take 849 showers for you to waste $1.00 worth of water. Keep that in mind if you choose a fancy way to solve your problem.
Customer Reviews
"I phoned you about my gravity loop that I recently installed. You clearly indicated what I did wrong. I had the theory and connections right, but the wrong pipe size. I used 1/4 inch copper tubing for the return loop. As you know, it did not work. Per your information I increased it to 3/4 inch pipe. You said 1/2 inch might work, but I didn't want to take the chance. Bingo! - It works beyond what I had hoped for - Instant Hot Water." Bob Chartier, Westland, MI
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"I remodeled about a year ago and read this column on gravity loops. We installed the loop and it works fantastically. There is instant, well almost, hot water on the far end of the house. I would not have believed something so simple could work so well....." Paul Wiegert
Hospitals, hotels, and other large buildings have used hot water recirculating loops for years. Some of these loops use electrical recirculating pumps while others use gravity. Based upon the fact that your water heater is in the basement of your home, Mother Nature is going to do the work for free!
Gravity hot water loops work because the heated water, which is lighter,
rises through the loop. As the water cools at the top of the loop, it falls and
is thermo-syphoned back into the hot water heater. The water enters the bottom
of the heater at the drain valve inlet. This flow of water is
slow but
constant.
For a gravity recirculating loop to work properly, the water heater must be located at the bottom of the loop. Ranch houses and two story houses with basements are perfect candidates. Houses built on slabs or that have hot water lines below the water heater must use a simple in-line recirculating pump.
All you need to complete your loop is a return water line from the far end of your hot water line. Locate the end of your existing hot water line. Cut into the pipe at this location. Install a tee fitting. One part of the tee will allow you to reconnect to the hot water line. The other portion of the tee fitting will be the start of the return loop back to the water heater.
Turn off your hot water heater's power supply before you start this project. Then turn off the water leading to the water heater. Drain the hot water heater and remove the drain valve by turning counterclockwise. Install a dielectric union or insulating nipple in place of the valve. This will to reduce corrosion possibilities if you are working with copper or galvanized iron water lines.
To save energy, you must insulate the entire loop. The insulation must start inches above where the hot water line leaves the water heater and must continue along the entire loop as it makes its way through the house and starts its trip back to the water heater. In new construction insulate all of the hot water supply pipe up to each fixture. Do not insulate the last 15 feet of pipe as it gets near the heater. This pipe must be uncovered to drive the convection engine that makes the hot water flow slowly towards this portion of the loop where the water is cooling because of its heat loss through the uninsulated pipe.
The insulation will slow heat transfer but can adversely affect the performance of the loop if you install it over all of the piping. Foam insulation is available which will slide over the pipe as you install it. You can also choose to use premolded fiberglass with a protective coating. The foam insulation is much more user friendly. Remember, to ensure good performance leave insulation off of the last 15 feet of loop piping as it returns to the heater. Be sure this is OK with your local energy code!
If the loop fails to work, water may be flowing backwards through the system from the water heater. You can stop this with a check valve. Install a check valve in the uninsulated part of the loop about 5 feet away from the water heater.
You MUST use a flapper-type check valve, not a spring-loaded one. Spring-loaded check valves will not work and block the slow trickle of water through the loop. Drill a 1/8 inch hole through the flapper so that a small amount of water can flow back to the heater to maintain circulation of the water within the loop. If the loop doesn't seem to work well, slowly increase the diameter of this hole but do not exceed 1/4 inch diameter.
Be sure your heater does not have a heat trap device at the top of the hot water outlet. These are small check valves that stop hot water from drifting up the hot water line when the hot water is not being used. Remove the heat trap device to get the gravity loop to work.
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Comments:
Greg S 05 Dec 2007, 17:02
We had a hot water gravity recirculation loop installed in our home about 5
years ago for our master bath. Since then I've noticed green staining
around the hot water faucet fixtures but never associated that with the
loop. This only occurs in the master bath. I thought I might have a PH
problem, but it was checked twice and in the normal range. I consulted an
expert in water quality systems. The first question he asked me is "Do you
have a hot water recirculation line?" It turns out that the green staining
is coming from the inside of our copper pipes. Apparently the constant
flow of water is wearing them down. This occurs mainly on the elbow
joints. I'm now in the process of figuring out how to safely disconnect
the line (I say safely, because I want to avoid a potential bacteria
problem caused by standing water in the return line). My pipes are inside
walls and under floors so I don't want them to last.
AsktheBuilder 05 Dec 2007, 17:19
Greg,
I would agree with that expert *if* the loop had a medium or high velocity flow. The gravity loops have a flow that might beat a turtle on a good day. Maybe you are getting erosion from the inside of that one faucet. If the expert is right, why don't we see oxidized copper at all sinks? Rhetorical question.....
Greg S 26 Dec 2007, 14:31
Thank you for your reply. Let me begin by saying that I'm not necessarily
convinced that I've discovered the problem or the sole source of it. I'm
certainly no expert on this and I am keeping an open mind. It's been
frustrating though as I feel the clock is ticking with respect to the wear
issue of our pipes. What I can say is this:
The staining only occurs in the master bath for which the recirculation line was installed. There are two faucets and a shower. We see the staining around both hot water faucets and in the shower. There are two additional bathrooms (one of them is also upstairs) for which we do not experience the staining problem. I agree that I wouldn't expect a convection flow line to create enough water velocity for noticable wear although I did notice that the valve going back to the hot water tank was nearly full open. I've since closed it way down after giving the faucets and shower a good cleaning so we'll see if that makes a difference (so far so good, but I think it's too early to tell for sure). Also, from my research, I have learned that there are other factors, such as water quality, that can affect copper pipe erosion. It's possible that there is more than one factor contributing to the problem. These factors include: - Poor water quality (dissolved C02, minerals, etc.) - Low PH (acidic) - Quality of plumbing joints (deburring, flux cleaning) - Electrical grounding issues I've tested my water twice (once professionally, the other time with a home test kit) and the PH is within normal limits so I've eliminated that as a potential cause/catalyst. Some of the water quality issues relating to "dissolved" materials would require more detailed analysis to diagnose. It probably makes little difference, but we also have a water softener. The softener was installed after the home was 5 years old so the insides of the pipes should be coated providing some additional protection. This makes it even more disconcerting that we are getting staining even with the coated pipes. I don't know about a potential electrical grounding issue or how to diagnose that. I have heard that a faulty ground connection can create electrical currents which in turn lead to corrosion. I can say that there are no visible signs of any copper pipes touching dissimilar metals (such as ductwork) and thus causing galvanic corrosion. I will say that the fact that it only occurs on hot water taps connected to the recirculation line leads me to think that the line may at least be a contributing factor. -- Greg
rob 17 Jan 2008, 14:37
my h2o heater is in the basement, i have a supply trunk running to the
second floor, dipping to the first floor then back to the second floor,
then back to the first, then back the the h20 heater. will a gravity
system work with that amount of up and down or do will i need a pump?
AsktheBuilder 18 Jan 2008, 06:55
Rob,
You need a pump and a winning lottery ticket. If the existing line behind the walls is not insulated, your fuel bills will be in outer space.
Terry L. Cook 07 Apr 2008, 11:55
Tim:
Thanks more than you could ever imagine for instructions how to install a gravity hot water recirculating system. We live in a rancher with our bathroom located at the far end of our home opposite about 50 feet from the where the gas water heater is located in an unfinished half basement below. It took over 45 seconds for water in the lavatory to warm-up. The wait was unbearable. Now, following your instructions, after running a ¾ inch return hot water line from the existing ¾ inch hot water feed line located beneath our bathroom in the crawl space, back to the drain at the bottom of our gas water heater, we now have hot water in our bathroom in exactly 3 seconds. It is unbelievable, but wonderful. With the water heater sitting in the basement 8 feet below the first floor of our home’s living area, there is a natural siphon created in the new return pipe. I increased the efficiency of the siphon effect by making a long loop curling downward to the drain of the water heater. Below are pictures of my installation, which ended up costing about $100. Below is a picture of the connection in the crawl space under the Bathroom. The “Tee” splice in the center runs from the existing insulated hot water feed line to an uninsulated pipe about six inches long to the left, to an elbow that begins the insulated return line back to the water heater. The other insulated lines are hot-water feeds, and the uninsulated lines are cold-water feeds to the lavatory and shower in the bathroom. Below is a picture of the return feed to the water heater, consisting of a cut-off valve on the top left, a flapper type backflow valve in the middle below, and a tee valve for the relocated drain at the bottom right. Below, with no insulation for a short distance as you instructed, is the extra loop coiling downward to the water heater above, installed to aid in the siphoning effect. Thanks for your help. Sincerely, Terry L. Cook
Howard 07 May 2008, 10:34
I have a ranch with a full basement and it is a perfect candidate for a
gravity recirc loop.
All the existing supply lines are copper. Will the gravity recirc work if the return loop is made of CPVC or PEX and is there a need to insulate these materials? Thanks, Howard
ever 12 May 2008, 00:19
hi,
is it possible to give gravity hot water return line, when hot water boiler is placed in roof of a 20 storey building. if it is not possible please give me the solution,please note that i just want to use gravity feed hot water return in my building.
Tom R 05 Jun 2008, 04:08
Tim,
I am interested in installing one of these systems. One question though. my water heater is in the basement. I have a bath on the 2nd floor more or less directly above the heater, the kitchen is also directly above the heater on the 1st floor, and there is another bath on the first floor at the other end of the house. should the hot water flow go straight up to the 2nd floor bath, down to the kitchen then over to the 1st floor bath, finally returning to the heater? or the reverse of that. in short, is it better to have the hot water path go up rapidly, then meander down, returning to the heater, or meander up, then rapidly down and return to the heater.
Rob "redlight" 05 Jul 2008, 09:45
So I have been living with the curse of instant hot water at my taps for
about three years now thanks to Tim's advice.
Howard, material should not matter. What does matter is insulation and the correct pipe size. Insulate all the way around, except for the last little bit. Tim the builder says the last 15 feet; mine works with just 4 feet of line exposed. Ever, you are probably going to need a pump if you want to have a recirc loop. Tom R, you a probably going to need two different recirc loops. I'm going to guess how your plumbing lines run but I would have to say that you will need a return line from your second story bath and a different return line from your far away first floor bath. View all comments |
