Return redesign question (with illustration)

adamfre

Good evening!
This is in regards to my 2 pipe, no trap, air vent system.

Being my ancient buried returns have collapsed, I'm trying to come up with a replacement strategy that involves me only having to bore in one wet return down the center of my crawl space, then connect all the rad returns over to it. However, I'm not sure I can do it this way and it not cause water hammer. Can someone take a look at the attached diagram, and let me know what you think of the design?

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Jamie Hall

Looks OK. The one thing you will want to do is to be absolutely scrupulous about the pitch on those "horizontal" dry returns. They mustn't be horizontal! They need to pitch at least a half inch and better one inch per foot of run. Towards that buried return.

It might be better -- and, perhaps, more convenient, if they dropped in at the top, or perhaps at 45 degrees on the sides, of the main wet return, though since all that is below the water line of the boiler it shouldn't make any difference, really.

Sounds like a nasty job...

Jamie Hall

Oops... one of our more vigilant members has pointed out that I meant an inch per 10 feet, not an inch per foot.

Senior citizens. Or Friday evening. Or something.

JUGHNE

Did you say in your other post that you couldn't do dry return because of the floor rad below the floor joists in the crawl space?

JUGHNE

Also, were you going to replace the boiler? If so then raising the new boiler up on concrete blocks would raise your water line and maybe solve some problems.

Note: Or maybe more problems. Did you measure the water level of the old boiler....center of sight glass off the floor?

adamfre

Thanks @Jamie Hall, I'll be sure to slope the horizontal runs at least 1" in 10'. I may do as you suggested, and make the slope steep and drop them in from the top. The job is going to be a HUGE pain, but it will be worth it. I'm actually enjoying the learning curve.
@JUGHNE yeah, everything is so tight with those in-floor rads, it pretty much prevents me from really moving much of anything around with regards to water lines.

JUGHNE

IIWM and those infloor rads were the cause of this tunneling job, I would examine how badly I really wanted to restore them. Perhaps appropriate above floor CI would do the job and still have the ascetics you desire.

I see your rad valves with the L-R nipple and no union. That makes the orifice installation challenging (which could perhaps allow you dry returns in the crawl space. Changing to a modern valve with spud nipple/union would change the ascetics also. Then there is always the possibility that your old valves could be beyond repair.....FWIW......just ideas.

I'm not sure why the 2 pipe air vent fell from grace, the extra piping was certainly the main obvious factor. But I thought I read about balancing problems even with dripped individual rad returns. I believe you mentioned this system had a history of open windows and some rooms cold.

Steamhead

Make sure each individual radiator return drops below the boiler's waterline before connecting to anything else. This will keep steam from getting into any of the returns. Then you can balance the system with the air vents.

It may make sense to run each individual rad return out of the crawlspace at a level just below the floor joists, then drop below the waterline in the main basement. This would minimize the amount of underground piping.

adamfre

That Borit tool is amazing. Bored my 30 foot hole in 15 minutes. Building the jig to keep everything aligned took me longer than the boring did. Slid in my pipe with pre-installed t fittings where I needed them, now all I gotta do is dig down to the fittings. Here's a link to a vid of me boring the last 10 feet.

https://youtu.be/wVpUhmc1YxI

SWEI

adamfre said:

That Borit tool is amazing. Bored my 30 foot hole in 15 minutes.

About once a month here I see some plumber or drain guy bent over a cutoff saw working through somebody's driveway or sidewalk. They could probably have bought a basic Borit kit for what they spent renting the saw. If the Borit can't handle it, call the trenchless guy. $50-60 per foot beats the tar out of a demo, trench, cover, and re-pave job.

Jamie Hall

Steamhead said:

Make sure each individual radiator return drops below the boiler's waterline before connecting to anything else. This will keep steam from getting into any of the returns. Then you can balance the system with the air vents.

...

And that, right there, is the key to making this thing work properly. Do that, and you're good to go.

Danny Scully

This may be a dumb question, but if you were going to have to dig down to the fittings anyway, why bother boring it?

JUGHNE

I think it amounted to avoid digging a 30' trench in a crawlspace rather than just one 24" deep hole. It all sounds like a young guy's job to me.