location of a manifold for new boiler going to feed radiators

PeteA

I plan on demo'ing all of the old piping in my basement and installing a new boiler and pex-al-pex throughout the basement to pick up the existing radiators. Does the location of the manifold matter? I was going to run 1-1/2 steel pipe across the ceiling and then over to the foundation wall to a good spot to mount the manifolds since the ceiling height in my basement is sooo low in this old house and it would be great to create some headroom since its an active basement. The run from the boiler would be approx 4 feet up to a 90 degree elbow, 8 feet of straight to the next 90 degree elbow down about 2-1/2 feet and then a 90 picking up the manifolds. so approx 14-15 feet total in each direction supply and return would add about 28-30 feet of pipe. I am anticipating I may have to put a vent at the top of the elbows where it turns down towards the manifolds but thats not a problem I should be able to fit the vents because of the way the floor joists run will keep them easily accessible. I'll upload a picture in a little while but in general is there any issues or concerns in general going up over and then down like that for a manifold or should I keep it on the ceiling to avoid trapped air issues?

PeteA

PeteA

you can see by photos 1 and 3 how low the ceiling is compared to the short 40gal hot water heater so all of the insulated pipes would be a great thing to eliminate from the ceiling. The middle picture is the wall I'd like to mount the manifold

EBEBRATT-Ed

The manifold location can be near the boiler or near the radiation. Makes no difference. I would use copper instead of steel pipe to run out to the manifold although there is nothing wrong with steel

hot_rod

How many btus are you trying to move? 1-1/2” may be more than you need

PeteA

@Bob I did a load calculation based on the radiators and the couple of pieces of baseboard I have a while back but I can't locate it right now but I do remember that the BTU calculation I did based on 160 to 180 degree water on the house showed that the radiators that were installed were sufficient but the old boiler was way oversized to meet the houses heating load. The heat loss calc on an 80 degree differential was just under 46,500. It's an old house but it's not too big and its heated by 5 average size radiators and 14ft of baseboard. I bought the 1/2 pex-al-pex since the general consensus by most people was that the 1/2 flows more than enough BTU's for a typical radiator. so the manifold will have 7 outlets/inlets to feed to radiators/baseboards individually.

hot_rod

So you need to move 4.6 gpm to the single  manifold. 1” copper tube with a 1” manifold would be adequate.

PeteA

@hot_rod Thanks Bob for all of your feedback and support you give on this amazing forum, it really is appreciated.
I already began assembling the manifolds out of 1-1/4 steel pipe (I misspoke in my earlier text when I said 1-1/2), each of my outlets has a full port 1/2 ball valve and the pex-al-pex fittings. I have not purchased any of the piping to go from the new boiler location (which will be the same as the old in my photos) to the wall where I'm hoping to mount the manifold . I'm assuming and hoping that it's OK to either run the 1" you mentioned would be adequate from the boiler over to the wall and then just slap in a reducer or should I do the 1-1/4 the whole way and avoid the extra 2 fittings. I don't imagine the reducers would be an issue in a closed water system but just figure I'd ask.
One other thing I was wondering about the pipe run from the boiler to the manifolds is, since I do have radiators in the house is there any benefit to heating up the small additional amount of water if the whole run was 1-1/4? I assume the 1" would be more helpful getting the water up to temp slightly quicker since it's less volume overall.
As always thank you all in advance for any feedback

hot_rod

Sure, use a reducer at the manifolds and run 1”

Again, with the assumption you only need 4-5 gpm to handle design load?

when you oversize the flow velocity drops. For hydronic work we suggest 2-4 feet per second

So with that 5 gpm or less the water moves very slowly. The air bubbles don’t move along the piping with the water flow at low velocity

Piping with 1” saves a few bucks also, could even use 1” pex

This chart shows flow velocity in 1-1/4 schedule 40 at various flow rated

 1-1/4 would like to flow 10 gpm or more

Alan (California Radiant) Forbes

You probably won't notice a difference or delay between using 1", 1¼" or 1½" pipe. You could almost use ¾" pipe for 4.6 gpm, but 1" is safe.

A heat loss calc. for your house will be fixed. You can play around with the ΔT (differential), but in your case, I don't think there's any advantage.

From what you've already said, it sounds as though your house has 1,800 - 2,000 square feet? What part of the country are you from?

Mad Dog_2

Awww...an Old Janitrol...1948? 1952?  Just guessing.  Love that original gas cock too!  Do me a Favor, atleast Pry off the Janitrol Emblem and save it.  It gave your home many, many years of service.  Mad Dog 🐕 

PeteA

@Alan (California Radiant) Forbes
Thanks Alan for the info and advice I'm doing this job at my house in New York. I used a pretty high temp difference in the heat loss calc just to be safe for the rare coldest dates which help me believe that you guys are spot on that as long as I'm moving enough gpm then I'll go with the 1" pipe. A little cheaper, easier to work with and readily available in most places in case I need fittings.

PeteA

@Mad Dog_2
I'll do that. The old unit is "working" but as I'm sure you are aware of the fire box below it has a huge amount of flame that just passes through the body of the boiler and then straight out the vent so the old workhorse is costing us quite a bit in the winter to run. I am sure that if I just reduced the size of all of the piping and kept the boiler it would be much better and probably have many more years of service. I put in the circulator years ago it it literally cut my $500 gas bills in half at todays prices those gase bills would have been around 6-700

PeteA

@hot_rod again I can't thank you enough for sharing everything you do. I'll be sure to share the final layout once I get underway.

hot_rod

A simple flue gas  temperature check tells a lot about efficiency 

Mod con flue temperature runs maybe 20 degrees hotter than the water temperature

I suspect that boiler runs 400F plus up the flue to the great outdoors😉

mattmia2

Wait, you replaced this? That would have outlived all of us...

PeteA

@mattmia2 I have no doubt that it still had many more year of life to it, but unfortunately the amount of gas that was being burned to heat the large volume of water in those pipes as well as the 6 sections of that boiler was just starting to get a little crazy again. We weren't even making the house very warm in the winters and that unit had to run for nearly an hour to just make the radiator warm so I had to bite the bullet and go right to the source of the issue and reduce the volume of water and increase my gas use efficiency.

mattmia2

Let us know how that goes. I don't think you're going to see a dramatic change, that boiler is probably around 10% less efficient than a modern ci boiler and the heat in the piping goes in to the house just more evenly.