Designing a DHW recirc line

Timco

I have two main 3/4” runs across the house I’ll draw back to the tank. Is a single spring check best or a swing check on each takeoff best? Bringing it back in 1/2” off a timed recirc pump and dumping it into the cold inlet. Thanks.

clammy

When I ve done portable re circ lines weather a single or multi recirc I use a single check on the outlet of the re circ pump . I ll usually put a balancing valve for each recirc line . I ll usually use a spring check over a swing chk . Aside from a timer I like a aquastat also no sense in pumping if the loop is hot. Peace and good luck clammy

MikeL_2

We put a check valve on the cold water inlet to the water heater, above the re - circ line tie in. We also put a check valve on each return before they merge on the way back to the water heater. A properly sized & connected thermal expansion tank is important, too. As others have noted, we like a timer & aquastat wired in series with the circulator. We insulate all accessible tubing.

Larry Weingarten

Hi, You might have a look at www.gothotwater.com. They have "demand" pumping, which uses FAR less energy than other approaches. Also, I like @clammy 's approach of balancing valves and spring checks. I'd stick with 3/4" return if you can to let the water move fast!

Yours, Larry

hot_rod

Ideally you calculate the heat loss from the loop to size the circ.

An ideal system might have thermal balance valves and a delta p circ

That way you recirc exactly what is required with ECM, low power consumption

Insulation! Saves time and energy loss
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_21_na.pdf

Timco

Thanks! I have the circ, Taco 006e 3 speed. I’ll add a aquastat to the timer too. Great idea. I’ll also switch to spring checks. Think I need one on the cold inlet too? Return is insulated 1/2” pex about 70’. Takes a long time to get DHW across the house to top floor or main floor. This will be a great addition.

MikeL_2

Be careful that the spring checks have the correct " cracking " pressure rating.....

BillyO

Caleffi 116 Thermosetter the way to go

hot_rod

Do you have a 3 way thermostatic valve at the water heater? What temperature are you keeping the tank at? 140F or higher is being suggested now for anti legionella protection.

If so the recirc needs to pipe like this to keep the temperature stable.

Another option is the AngleMix valve to the right of this post, it is a 100% shutoff valve that prevents "creep"

If you check the incoming cold, need to add a thermal expansion tank. Low lead checks everywhere of course

Timco

> @hot_rod said:
> Do you have a 3 way thermostatic valve at the water heater? What temperature are you keeping the tank at? 140F or higher is being suggested now for anti legionella protection.
>
> If so the recirc needs to pipe like this to keep the temperature stable.
>
> Another option is the AngleMix valve to the right of this post, it is a 100% shutoff valve that prevents "creep"
>
> If you check the incoming cold, need to add a thermal expansion tank. Low lead checks everywhere of course

Yes there’s a 3-way. I guess I’m not seeing the reason to pipe to both cold pipes and the extra check? My local supplier did not have the valves shown. I had not planned on a check on the incoming cold because I’m on a well and was going to use the well tanks for expansion. Thanks!

ChrisJ

MikeL_2 said:

Be careful that the spring checks have the correct " cracking " pressure rating.....

What is the correct cracking pressure rating?

MikeL_2

I'm not sure; hot rod will know. I didn't know what cracking pressure was until I had an issue with a chattering spring check a dozen or more years ago. My source for spring checks at that time didn't know either.

hot_rod

MikeL_2 said:

I'm not sure; hot rod will know. I didn't know what cracking pressure was until I had an issue with a chattering spring check a dozen or more years ago. My source for spring checks at that time didn't know either.

For hydronics you want a low "pop" so a small circ can open it. DHW typically has more delta P to open checks.

Here are the ranges we use, for this dual purpose hydronic potable water serviceable check.

hot_rod

Timco said:

> @hot_rod said:

> Do you have a 3 way thermostatic valve at the water heater? What temperature are you keeping the tank at? 140F or higher is being suggested now for anti legionella protection.

>

> If so the recirc needs to pipe like this to keep the temperature stable.

>

> Another option is the AngleMix valve to the right of this post, it is a 100% shutoff valve that prevents "creep"

>

> If you check the incoming cold, need to add a thermal expansion tank. Low lead checks everywhere of course



Yes there’s a 3-way. I guess I’m not seeing the reason to pipe to both cold pipes and the extra check? My local supplier did not have the valves shown. I had not planned on a check on the incoming cold because I’m on a well and was going to use the well tanks for expansion. Thanks!

Yes you should be fine for thermal expansion and not need the incoming check. Check mainly assure proper flow, and handle pressure imbalance across a thermostatic valve or example.

ratio

hot_rod said:

Here are the ranges we use, for this dual purpose hydronic potable water serviceable check.

Are the unions symmetric? I can see wanting them to be non-reversable for when I do it right the first time; but I can also see wanting them reversable for those times when I do it right the second time!

hot_rod

yes it could be installed backwards, unions are the same on both ends.

Timco

Well, tomorrow will tell if dumping the recirc into the cold feed to the tank right at the tank connection will suffice. I’ve been on other projects and tomorrow I change it all over. I’ll post pics when done. Thanks for the feedback!

Timco

Quick update. I figured why ask questions then not follow the advise? I split the recirc return into two directions and added a check on the CW feed to the 3-way mix valve and dumped one recirc return on the 3-way side of that check and left one at the CW makeup to the tank. Works great. If I run the recirc pump over speed 2 the check rattles below the pump but it does great on speed 2 anyway. The aquastat kills the recirc when it gets to about 115. Later when it all cools down I’ll time how long it takes to make it all the way around and set the time clock. Thanks for the input!!

Timco

Timco

Funny thing is it works great if I cut off the return that ties into the CW temper line to the 3-way...if that line stays open and the recirc pump is off that line turns ice cold and I get tempered water to fixtures. With that closed it works great. The 3-way decides if it wants recirc return water or tank water.

rick in Alaska

I like to put a drain valve past the check valve on the pump, and then a ball valve, before it ties in to the cold line. That way I can purge the air out of the recirc,and it also makes it easier to check for a stuck check valve in the future.
Rick

Alan (California Radiant) Forbes

rick in Alaska said:

I like to put a drain valve past the check valve on the pump, and then a ball valve, before it ties in to the cold line. That way I can purge the air out of the recirc,and it also makes it easier to check for a stuck check valve in the future.
Rick

That's a great idea, but wouldn't you want the drain before the check to confirm check valve operation?

ChrisJ

Alan (California Radiant) Forbes said:

rick in Alaska said:

I like to put a drain valve past the check valve on the pump, and then a ball valve, before it ties in to the cold line. That way I can purge the air out of the recirc,and it also makes it easier to check for a stuck check valve in the future.
Rick

That's a great idea, but wouldn't you want the drain before the check to confirm check valve operation?

Isn't there an arrow on them?
It wouldn't let you drain the tank either, no?

rick in Alaska

You want it to be the very last thing before it goes into the tank. That way all the water and air has to go through the pump and the check valve. Then you know there’s no blockage.
I have had a few check valves seize up a little so they wouldn’t open, and this would prove it.If the check valv was stuck open, you can usually tell by feeling the pipe before the pump with a fixture running and see if it starts feeling cold.Or you can loosen the flange on the pump after isolating the returning hot water, the open up the valve set the check valve. If the valve is good, you should not get any water at the pump.
Rick

SuperTech

@Timco That's nice looking work. I appreciate the fact that it's all done in soldered copper and insulated. Good job!

ChrisJ

SuperTech said:

@Timco That's nice looking work. I appreciate the fact that it's all done in soldered copper and insulated. Good job!

In my opinion, insulation is not optional on a recirculating setup.

Also, pex by nature loses less heat than copper. Around the equipment where things need support etc I think copper is a must, but for the rest of the loop it's not automatically better in the big picture. There's trade offs for each material.

Timco

SuperTech said:

@Timco That's nice looking work. I appreciate the fact that it's all done in soldered copper and insulated. Good job!

I finished the insulation today. Thanks. This replaced a Amtrol tank that was acting like a huge radiator it was so hot to the touch. A purge station would have been wise. The long return line is Pex but all else is copper. The water heater is off the end of the manifolds with no ZV and our DHW was always very hot. Then I noticed the tank temp was always way over 150. I realized the tank was heating with each CH call and the old tank had no 3-way so we had scalding water in the house. I added a check which helped but I’ll repipe when heating season is over.