Single main, gravity hot water

Steve Minnich

We recently installed a couple of KHN110's in a 125 year old house. Cleaned up the old near boiler piping which was converted to a pumped system a long time ago. And by clean up, I mean we gutted everything because it was that bad. No issues with the way our new system is operating.

The owner now wants to finish the basement and wants more head room. Currently there is a single 4" main that splits the middle of the basement and then splits to 3" mains that wrap around the basement and returns to the boiler room.

22 radiators total. Looks like all supply branches are tee'd off the top of the main while the returns are tee'd off the side the mains. Makes sense. I plan to remove all the main piping and cut and thread the branches and as high as possible. Looks like I can get a Ridgid 600 inside the joist spaces in most places. Then, a home run manifold system.

My question is this. I'm thinking a specific radiator's supply and return is going connect to the main in relatively close proximity of one another? I've looked at gravity system piping schematics and have seen it done that way and other ways. What do you think I should expect?

SWEI

Sounds like it may be a single pipe counterflow gravity system. Got any photos of the takeoffs?

Steve Minnich

These aren't the best pictures in terms of what you're looking for. I took them during the site visit for my bid.

SWEI

Do the takeoffs & returns look similar to these?

Steve Minnich

Yes.

Paul48

If there's any question Stephen....why not use compressed air to confirm you're on the same radiator?

Steve Minnich

Yup, that's what I will have to do. Trying to avoid the inevitable black spray.

Harvey Ramer

That's what a shopvac bag is for.

Paul48

Since you mentioned it............maybe it's a good time to flush the rads?

SWEI

The pictures above are radiator takoffs from a single pipe counterflow gravity main. You basically have two options:

1. Work with it: Pump the main as slowly as practical and run a tight ODR curve. On that job, we used a VR1816F on the lowest (5 feet) constant pressure mode and three Belimo CCV's (proportional zone valves) with a 154k (net) fire tube mod/con boiler. I doubt that conventional zone valves would produce good results. BTW, you can flush 'till the cows come home and it won't do much to the rads. We got a lot of crud out of the mains and installed a a Dirtmag on the return. It burps a bit of brown water every few weeks, less and less as time goes on.
   
2. Replace it: Rip out the main and re-pipe the runouts in parallel (hopefully reverse return.) This would allow you to power flush the rads.
   

Paul48

He could do it the way he said in his first post also.