what would water do? (direct return question)

sarah_4

My system is currently a 1-zone direct return rad setup. I'm adding a new zone (using a circulator) which will be a continuous loop up to the attic. I'm also adding 2 rads to the existiong zone.

Question:

Can I tie the 3/4" return of the new zone into the 1-1/4 return of the existing zone just after the last rad on the 1-1/4 zone?

Since the zones will be pumping away, I can't think of any reason to carry the 3/4 return all the way back to the boiler ( a good 75') before tying in--not when there is a perfectly good section of 1-1/4 return a mere 3' away from it.

But I'm not sure I've ever seen this done, either, so wanted to check with the the guys who KNOW.

Attic loop currently feeds a cast iron rad, but I may change it to a loop of baseboard in the future.

(It will not be piped pri-sec--I did the math, and couldn't get enough of a temp. savings without endangering the boiler to make it worth it.)

As always, thanks for your help--it is invaluable.

Sarah

sarah_4

Mike T., Swampeast MO

Is this rougly what you're talking about?

If so, I don't believe there will be a problem as long as:

1) No radiation after the connection is made to the return main.

2) Common portion of the main is adequately sized for combined flow of both circulators.

p.s. I drew the new zone as two-pipe direct return, but a one-pipe loop should be OK as well.

sarah_4

Mike,

Yes, your drawing was EXCELLENT! However, I wanted to tie in the return of the new zone between the "top two" returns on your drawing. I --disappointedly--accept that this won't work, but I don't understand why. would it work if I ran smaller piping for the main that feeds the top two and then increased it back to 1-1/4? (the whole thing is oversized anyway--old house) is it an issue of velocity, or pressure, or what?

thanks--

sarah

Mike T., Swampeast MO

Like your Topic name \"What Would Water Do\"

Having never seen this either, I'm trying to think along those exact lines.

To get circulation your pressure on the return side has to be lower than that on the supply side.

In a direct return system those rads farthest away naturally have the longest (and consequently most restrictive) path. The water will try to follow the least restrictive (shortest) path, but as long as the differences between the restrictions through each radiator path are slight, you get full and reasonably balanced circulation.

If you make the return connection in the "middle" of the radiation branches I believe that some of the head pressure of the new zone's circulator will "show up" at the point where you connect to the return main. When/if that happens, the motive force for circulation in the radiator circuits BEFORE that connection point (in other words those farther away) will be diminished. While the overall flow through the main circuit shouldn't be affected too greatly, I believe more of the total flow will tend to circulate through those radiators after the connection point and less though those radiators before.

p.s. 1¼" mains really aren't that big when compared to gravity systems (the general type that I work on). Given the lengths you mention, the system was certainly designed for forced circulation.

p.p.s. I'm most certainly open to correction in this matter as, again, I'm just "trying to think like water".

p.p.p.s. The above assumes that the new zone's circulator increases the pressure at it's connection point to the return. If it reduced the pressure I believe the opposite would happen. The point is that I believe you're almost certain to change the pressure somehow at the point where you connect to the return main. As long as you connect after all of the radiation, there will still be a change but it should affect all of the radiators similarly.

sarah_4

now I get it

Your explanation makes a lot of sense. High pressure goes toward low, just like with steam. so unless someone else corrects you, I'll pipe it as you suggest. thanks for your help!

Paul Mitchell_2

I agree

Basically I think if you tie in before the last rad you might get some flow where you dont want it. I noticed your posts on the "starting own business" post. Are you a heating contractor?

sarah_4

what I am

I work for myself as a plumbing & heating contractor in massachusetts. In mass. there is only one license for both--what I actually do is about 75 % plumbing and 90% service and repair. I've been in business a year and a half and I'd never done any major boiler work before (to me, redesigning a system and adding a zone is major) but this boiler is in a family member's house so I thought it would be a great chance to learn a lot. I'm happy to say it's going well, thanks largely to the help and feedback I've gotten on this site. I did my apprenticeship with an "old timer" plumber who knew a lot about troubleshooting and repair but did not do a huge amount of heating or remodeling. So this has been a big learning experience for me. I am considering attending the I B R heating school weekend in boston in october...feel like I'm ready for it now.

Paul Mitchell_2

I went to the IBR school

and enjoyed it a great deal. Honestly prior to that you should get Dans book package and read it all. Will be a great prep for the class and great future referance material. As you have found out this is the best site for help and fellow tech consultation.
Good Luck
Paul