Domestic hot water return line sizing

Mad Dog

How do you guys pipe it. Do you return in to the bottom of the heater? Hot Rod is 100% right. I've used a taco 006 and I think it was too big because it was so noisy and hummed alot. Who makes a pump that would be quiet? Thanks MD

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CanAm Jim

Domestic hot water system return line sizing

This is not an HVAC related question, but I'm sure that some of you who frequent The Wall will be able to help me. I am trying to locate accepted engineering methodology information on sizing recirculating hot water return lines in single family homes. I am currently "debating" with a building official who believes that the hot water return line must be equal in size to its supply line. There is no heating demand on this system. It is designed solely to reduce time and water wasted waiting for hot water to move from the hot water heater to remote plumbing fixtures. The plumbing code in our area is the Uniform Plumbing Code. Unfortunately, it does not address hot water return piping and its sizing in any way.

Thanks for your help.

hot_rod

The same size!?!

If it's not in your local code addendums and not in the code book, he gets no say in what you do other than to make suggestions! If I had had to run my recirc line (which is a 1/2" gravity system BTW) the same size as my main hot water feed line, it would have been 1", which would have been a waste of time & money.

If you set it up as a gravity system, 3/8" can work quite well. We've got plenty of pumped and gravity systems that utilize 1/2". My swing check on my gravity system has a 1/4" hole drilled through the gate, which regulates the flow down to a trickle.

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Unknown

Not sure of local codes

but we used to install commercial steam boilers in buildings with 30+ apartments in NYC , and the biggest existing recirc pipe we saw was 3/4 , and most often they were 1/2 . Every one was gravity recirculation . The cold pipe was usually 2 inch , with the hot going to the apartments in 1 1/2 .

jackchips_2

Here in Ma.

the code requires recirculation or heat maintenance if a fixture is more than 100 feet from the heating source. There has been conversation of decreasing that to 50 feet which is probably a good idea.

As far as the size, there is a formula that ASPE puts out if he requires you to put a line in. I can assure you that the size Dave mentions would be more than adequate especially if you install a circulator and aquastat.

Sounds like he is overstepping his ground. Ask him to show you the section of the code that requires a line and how it should be sized.

Jerry Boulanger_2

The flow required need

only be high enough to overcome the heat lost in the piping, and should be low enough that it does not erode the pipe and fittings. If the pipe is insulated, a trickle is truly all you need. Remember that smaller pipes have less surface area and lose less heat, so a larger than necessary pipe in this application can actually waste more energy. I usually recommend 0.5 gpm for 1/2" pipe and 1.0 gpm for 3/4" pipe, and use automatic flow control valves to limit the flow to those values.

Mike T., Swampeast MO

Exactly how I did mine

1" supply, ½" return, gravity operated.

Works perfectly.

hot_rod

Very low flow

is needed, and insulating both supply and return lines is wise. I have seen 3/8" (1/4" ID)pex and even 3/8" soft copper used in residential recirc lines.

Also the smallest pump money can buy is usually adequate. The timered version of the small recirc pumps spec at 0-3GPM at 0-5 feet of head.

Grossly oversized pumps are the most common mistake I see on DHW recirc systems.

hot rod

CanAm Jim

A little more info...

We are here in the beautiful state of California, land of "fruits" and "nuts", if you know what I mean. I thank you all for your input, and I agree with you all 110%. Unfortunately for me, if this inspector were to read all of your threads, he would tell me that you are all piping these incorrectly as well. Here is a bit more info...This inspector is hiding behind the "Administrative Authority" clause in the UPC, which pretty much gives him authority over how the system will be designed if the code does not address it. The systems (a tract of about 400 homes) are insulated Wirsbo AquaPEX supply and return piping with Grundfos UP10-16BU circulators (pretty quiet) moving about 1.5 GPM or less. The returns will be connected to the bottoms of the water heaters.

I am looking for some sizing guides giving specific details on sizing returns. I am particularly interested in Jackchips reference to a formula published by ASPE or something like it that I can hand to this inspector to back us all up.

Thanks again to all for this overwelming response.

heretic

Grundfos Comfort

A friend has one of these Grundfos UP10-16B 'packaged' deals with a thermostat and timer. Super quiet.
I'm considering the merits of that vs. just gravity.
See 2nd attachment for install diagram.

Dave Yates (PAH)

You've got friends at Wirsbo - use them!

Fly Wes out to have a visit with your inspector! One look at those arms & the inspector will be saying "Yes sir"(G).

Seriously, give the Wirsbo folks a call. They are great when it comes to customer service and will, no doubt, be more than happy to help educate your inspector. Who knows, (s)he might just appreciate your helping him/her wade through what must be confusing and foreign to their limited knowledge in hydronics.

If all else fails, fly Cindy out and let her give that inspector one of her smiles. He'll melt like butter in the mid-day sun of August!

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Mad Dog

Thanks Corey...yeah before I close up the walls in the house

I think I want to do a hwh recirc line - either gravity or pumped, but I've never had much luck on residential recirc lines...they always wind up buzzing alot or humming through out the house. I've tried all kinds of check valves, the lies were not full of air. I think the problem was the 006 is too much pump for the average residential system. I think the gravity one will be fine ...the water heater is really no further than 25-30 feet from the farthest fixture, so it really isn't necessary, but I just kinda wanted to experiemnt . What you boys think??? Mad Dog

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Alan(CaliforniaRadiant)Forbes

Mad Dog

If the return line is that short, use a 003.......... and we take it back into the cold supply line instead of the drain. It makes it much easier to deal with when you have to change the water heater out.

Can Am Jim: I think you guys belong to the same association as we do (PHCC) here in the Bay Area. I've always heard that inspectors cannot randomly make up code requirements; if they require stricter codes than what's in the book, they have to have it in writing. I'd talk to his boss since what he's requiring makes no sense to me. The purpose of a return line is just to move water, not supply fixtures.

Best wishes,

Alan

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Mad Dog

Why thank you Mr Forbes...didn't know they

made a 003. how about gravity only do you like that. PHCC ALL THE WAY!!!! Mad Dog

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Alan(CaliforniaRadiant)Forbes

Well, heck

yeah; gravity is the best, but more often than not gravity won't work if the return line is anything but vertical.

It happened once that we had a long horizontal run; we sloped the pipe down to the water heater connection and still needed a pump becuase there was too much friction on the pipe (¾").

And there was the time I was convinced that we needed a pump since the return line had to go uphill at one point; we installed a pump with a timer and found that water circulated when the pump was off. We removed the pump and had a gravity system.

Taco recommends a 003 when the loop length is under 200'; a 006 when there's a 200' - 400' loop length.

We always like to install a ¾" return line. Not only does it reduce the drag on the pump or gravity circulation, it increased tha capacity of the hot water system by the amount of water in the pipe (0.0269 gal./ft.).

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Larry Weingarten

recirc

Hello: Maybe you should consider getting an engineer to do the heat loss calcs, size the pipe and put his/her stamp on it. That way the inspector cannot be faulted and you'll only need a small line.

steve gates

This is the

only one I use now. But with the unions.

I saw a 43-75 on a 1/2" once...da must be why we were there to replace the line.

jackchips_2

Jim,

the ASPE formula is not for residential applications and would have little or no relevance to a domestic home application. There are a number of steps involved with a few assumptions. It also involves circulation rates, allowable friction head loss, total head required, rate of flow, etc., etc..

Alan has given some sound advice on how you should proceed.

Good luck,

Jack

ScottMP

Reminds me

Of the job we installed a bathroom at the end of a large greenhouse, about 80 feet away fromt he tank. Put a Lang pump in. I came back about a week later to check it since the electrican needed to add a plug for us. When I checked the hot water it was right there. You got it, the plug still was'nt installed. Gravity with a horizontal run of about 80 feet and 15 foot rise. I have allways gone in the bottom of the tank to use the water density in the tank.

Scott

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mp1969

return lines

Wetheads,
If you use a pump and hook up a recirc (Let's say in an apt.building) do not use type "M" hard copper or anything thinner. We have replaced a great amount of Swiss cheesed
copper recircs. One of the biggest boosts to Aquapex and other pex piping was the failure of the thin "M" copper in especially the hot side of domestic water distribution systems. Some of this is due to pump oversizing but trust me that is probaly done far more than undersizing!
If I design a commercial job or even a large residence I try to use a looped system where the hot water loops a building and gradually is sized down to a 1/2" return to the heat source> Works great!

Have a good one!
MP 1969

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