DIY Home Improvement Forum banner
1 - 20 of 30 Posts

·
Registered
Joined
·
1 Posts
Discussion Starter · #1 ·
I've now read a lot about the high expense of running a hot water recirculation system. With the benefit of hindsight, I would have not bothered with it. My system was installed by a professional plumbing firm but I am now questioning this. We use a standard 40 gallon natural gas hot water tank.

We first noticed that it was difficult to fill our bathtub with sufficient hot water. The water was instantly hot as expected but after a few minutes the temperature would drop to the point of being only warm. Suspecting that the recirc system was the cause, I disabled it (closed the valves to the loop and turned off the pump) and
allowed the tank to become fully reheated The tub now fills with plenty of hot water. I am now trying to understand why.

My theory is that when hot water starts to discharge from the tank (from the top) cold water is being put into the tank (at the bottom). Hot water rises and cold water sinks and so the two should remain relatively far apart so that only hot water is being discharged from the top until most of it has been used. However, with a recirc pump continually running the water in the tank is being stirred, mixing the hot and cold to produce warm water. Does this explain my situation?

With the pump running we have also noticed that the tank is being reheated many times during the day and night when no water is being used. During the building stage I made the suggestion to insulate the hot water lines but I was told that this was not needed. I also questioned placing both the hot and cold water lines too close together but was told this was also unnecessary. Our home is only 3400 feet on two levels and the tank is centrally located. Unfortunately, we now have warm water when we use the cold water (until enough water is used), we have high energy bills, and we have a warm bath. We do, however, have instant hot water!

I have since disabled the recirc system and have accepted waiting a few seconds for the hot water to arrive.
 

·
Registered
Joined
·
601 Posts
there should be 2 check valves on the hot water recirc system. One on the recirc pipe and one on the cold inlet before any tees to the recirc pipe. my first thought is that you have a bad check valve or are missing one. the pump can create negative pressure, sucking cold water into the recirc line and eventually to the fixture being used
 

·
Premium Member
Joined
·
11,949 Posts
Recirc systems do work when properly plumbed. I suspect that your heater is too small for a 3400 SF house
 

·
Registered
Joined
·
1,117 Posts
During the building stage I made the suggestion to insulate the hot water lines but I was told that this was not needed.
Seems to me that this is your problem. It's logical that in a hot water recirculation system both the hot lines to the fixtures and the return lines from the fixtures need to be insulated to prevent losing heat. In the perfect situation the water returning to the heater would be just as hot as when it left the heater. Of course this is not possible but insulating the to and from lines would work toward that goal.

I would insulate the entire hot water and return lines and then see what happens.

EDIT: To add to my reply, I think your uninsulated lines are working like a car's radiator. In an engine, heat is transferred to the water, then the hot water is sent to the radiator for cooling, then the return water to the engine is cooler. --- In your case, gas or electricity is heating the water in the water heater, then the hot water is sent to the long pipes (or tubing if PEX) which act as a car's radiator, and then the cooled water is returned to the heater. Your uninsulated system is working to cool the water in the heater.
 

·
Registered
Joined
·
33 Posts
It sounds to me like the recirc system is incorrectly installed. Can you take some pics of what they installed and post them? Whats does the plumbing company say about this?
 

·
Registered
Joined
·
133 Posts
Your main issue is the insulation like others have mentioned, A hot water recric system is typically designed for a 10 degree temperature drop, so for example, the water leaves the heater at 120 degrees, flow through the supply and return piping and should return to the heater at 110 degrees. Without any insulation on the hot water piping, and depending on the length of the loop, your probably getting return temperatures around 80 degrees. You should also have an aquastat on the return leg which controls the pump, so when the return temp reaches a set temperature, it shuts off the pump. Your pump is probably running 24/7 because the return temp is not getting up to the set point because of the heat loss from no insulation. Also, you could consider getting a timer to control the pump during specific hours during the day, so the pump only runs in the morning and in the evenings while people are home to help limit energy loss. All this depends on the size of the loop and the gpm of the pump.

Also, you mention getting warm water out of the cold tap, that tells me you have hot water bleeding into the cold side somewhere close to the heater where the hot return and cold lines are piped back to the heater. There should be a check valve on the cold side before the hot return line ties in to prevent this, you should also have an expansion tank on the system because of the check valve.

If you could post a pic of the connections to the heater and the hot return/pump/valve configuration, that would help.
 

·
Registered
Joined
·
9,618 Posts
Stirring of the water in the tank is not (should not be) a problem because for those folks without a recirculation system the same stirring of water occurs when you turn on a faucet and cold water enters (hopefully) at the bottom of the tank to replace the hot water being drawn.

If only one person is using hot water at a time, the square footage of the house doe snot matter.

Getting lukewarm water from the hot faucet too soon, and/or getting warm water from the cold faucet with the recirculating system running and not with the recirculation system valved off means the system needs some mods (like check valves).

Getting a few minutes of hot water followed by lukewarm water is not a pipe insulation problem. But you should still insulate the full lengths of the pipes to minimize heat loss into the spaces inside the walls where the pipes run.
 
  • Like
Reactions: CaptTom

·
Registered
Joined
·
33 Posts
Here are some pics of what mine looks like for your comparison. It works like a champ, I have hot water at every faucet in under five seconds. Starting at the wall there is a ball valve, recirc pump, check valve, thermostat and then it tees off into the water heater and a drain spigot. That is also the flow of the water, from the house through the pump and back into the tank. I have no check valves on the top of the water heater only a ball valve on the inlet side. At this point insulating your pipes would probably pretty costly and labor intensive. I would make sure the system is plumbed right before anything else. Hope this helps and you get it all straightened out.
 

Attachments

·
Registered
Joined
·
3 Posts
The need for a check valve seems clear. Is there a certain type, e.g., brass, or manufacturer that would be best? Are these valves OK with hot/warm water? My line is 3/4 in pex.
 

·
Registered
Joined
·
3 Posts
Just to tie up my question about the check valve for the hot water recirculation return line, I went to a plumbing supply store and was directed to a Campbell 3/4" check valve (CV-3T, $12).
 

·
Registered
Joined
·
8 Posts
My recirculation system works great on my home which is 3440 sq. ft. all on one level but with the water heater in the basement. I insisted the plumber insulate the hot and return lines and the first six feet of each fixture feeder hot line when we were building the house. Without the recirculation line working it takes almost two minutes to get the master bath shower warm enough to get into. During the summer I unplug the recirculation pump and gravity takes care of the recirculation (hot water rises to the fixtures in the living area above). It takes about three seconds to get warm water anywhere in the house. We also use the water heater to heat our home during the winter using an air handler. When it is running I need to turn on the recirculation pump to keep the recirculation line working since the air handler temperature drop messes up the gravity recirculation. My recirculation pump has a built-in, adjustable, thermostat so it turns off when the recirculation line is warm and I have a check valve in both the recirculation line and air handler. I also keep the pump on a timer so that we don't run it 24/7 during the winter--that saves energy. During the summer our propane usage drops to about 1 gallon per day and I think much of that is due to the recirculation line losses. I'm going to add some additional insulation to the hot and return lines this winter to try to cut that down some. It is costly to use recirculation but waiting two minutes for hot water daily is unacceptable, especially to my wife! Your plumber made a big mistake telling you the hot and return didn't need to be insulated and not making sure check valves were in place.
 

·
Remodel and New Build GC
Joined
·
10,446 Posts
there should be 2 check valves on the hot water recirc system. One on the recirc pipe and one on the cold inlet before any tees to the recirc pipe. my first thought is that you have a bad check valve or are missing one. the pump can create negative pressure, sucking cold water into the recirc line and eventually to the fixture being used
Recirc lines/systems all somewhat differ and can be affected by your runs/elevations/drop/rise etc.

While we can not actually examine your system, feel the pipe temperatures as they are occuring etc.....

I am almost certain that THE MAN above is dead correct


My next door neighbor had almost exact same issue with his recirc.... they would get in the shower to hot water.... and a few minutes later it got significantly cooler.

The check valve (only one on his system) was stuck open.... and the negative pressure of turning on the hot was backfeeding his cold line back into the shower.

(If a recirc line was not involved, I'd guess your issue might be the dip tube in your water heater.... as in principle you were wondering about in your initial post)

On my present home in southern Nevada, I have a recirc line.... but I don't want it running all the time... wasteing energy and additionally competeteing with my A/C.

I put the Grundfaus pump on a remote control clicker plug in unit ($15 at HD or Lowes), so when my wife wants immediate hot for the WM or just at the kitchen faucet, she clicks in on 5 minutes before...... or if it a regular need, like showers in the morning, put the pump on a timer.

Good luck
 

·
Registered
Joined
·
1 Posts
I always put a check valve on cold inlet and also recirc line..never had a problem with 25 years of experience. Also if you have problems with new installation of fixtures suck as a touchless kitchen faucet you may need a check valve at the faucet location if you leave the handle on at your desired temp,when not in use there could be mixing..also any plumbing fixture that has a divertor after the hot and cold shut offs.
 

·
retired framer
Joined
·
50,985 Posts
After you have it figured out set it up with a smart switch so you can turn it on for the few minutes before a shower or what ever. I am sure the phone could be programmed to turn it off after how many minutes it needs to deliver the hot water.
Then you have saved the heat bill as well as the water bill.
 

·
Remodel and New Build GC
Joined
·
10,446 Posts
I have a grundfaus recirc pump, and plugged it into a $9 standard-stock remote control from HD or Lowes with an on/off switches.

Sits in the kitchen drawer and we turn it on/off as needed.
 

·
Registered
Joined
·
4 Posts
This sounds a lot like some issues i am having with my system. Can the re-circulation pump also cause an increase in water pressure while the water heater is also heating? I have unplugged my re-circulation pump and have seen water pressures return to what i assume is normal 40psi-60psi (60psi when heating). VS 110 PSI when heating with recirc pump installed.
 

·
Registered
Joined
·
8 Posts
The recirculation pump is quite small and would not be able to pressurize the hot water line significantly. If you're seeing that sort of pressure increase the only thing I can think of that's associated with the recirc pump is that it is causing the water in the hot and return lines to heat up quite a bit when you turn it on from cold causing the water heater to run more to supply that heat. When water heats it expands and if there's no hot water being used that expansion could cause the pressure to go up dramatically since there's no air in the system to compress and water is not compressible. Typically there's a small expansion tank in the hot water system with an air bladder that absorbs the expanded water and keeps the pressure from rising much. My hot water expansion tank is only 1.5 gallons, I think, and I never see a pressure rise under any conditions. I insulate that tank to reduce the heat loss also. Check and see if you have an expansion tank connected to the hot water line. If not, I think that's the problem.
 

·
Registered
Joined
·
4 Posts
Thanks for the quick response Jim.

I do have an Expansion tank. I can't tell exactly where it lands in the system as the connection that comes to it is coming out of the wall. Since i have unplugged the recirc pump, and closed the valve that feeds to it i haven't had any build up of pressure. I was seeing the same issues that were talked about previously in this thread. Hot would output warm water at best, and occasionally cold water would spit out hot for the first 5-10 seconds. so far with the recirc unplugged just a long long wait for hot water can be upwards of 3-5 minutes of running water, but once hot water arrives it is HOT:devil3:

Previously i thought my expansion tank wasn't properly charged, i had checked it and it seemed properly set.
 

·
Registered
Joined
·
1,822 Posts
I've heard of people hooking them up to the bathroom light switch, or motion sensor, so they only start when someone enters the room. Presumably, they've done their thing by the time that person turns on the hot tap. Admittedly, I've never seen that arrangement, but it makes some sense.
 

·
Registered
Joined
·
8 Posts
Touch the bottom of the expansion tank to see if it is warm. If not, it may be on the cold side of a check valve feeding water into the water heater where it can't absorb the hot water expansion. An easy test to do is to leave a hot water faucet on very low and turn on the recirc pump. That will keep the pressure under control and verify that the increase in pressure was due to water heating. If the expansion tank is in the wrong place you may be able to add small one anywhere in the hot water line more easily than replumbing the existing one. The expansion of the water is very small but in a sealed system that can raise the pressure a lot. There is a pressure relief valve on every water heater that will open to let water out if the pressure gets too high. That may be what's limiting the pressure to 110 psi when the recirculation pump is on.
 
1 - 20 of 30 Posts
Top