Dividing a Zone/Boiler Replacement

jad3675

My house (1951) has ~2450 sqft of finished, above grade living space heated with 3/8 copper tubing embedded in the scratch coat of the ceilings. I've done some rough math and I think I have around 5K feet of the tubing in the ceilings. Unfinished basement (1540 sqft) has heat provided by floor standing slant/fin-ish enclosed radiators. Hot water for this system is provided by a 21-year-old Dunkirk XEB-4 boiler that I don't think is quite setup right.

All three floors are one zone. The two above grade floors are fed by 1 1/4 copper manifold in the basement that has 18, 3/8 runs come of it that feed the radiant tubing. The return for the system is a bit of a mystery - there's a 1 1/4 copper return line that comes down from the finished ceiling in the basement and makes it way to the boiler. I fear the manifold(s) for that is somewhere in a wall. The basement radiator boxes are fed by 1/2 copper that tee off the boiler supply (before the manifold), though one is fed at the end of the manifold.

My main problem with this setup is well, it's one zone. With the only thermostat (1st floor hallway) set to 67 the 1st floor will get to 67. But the 2nd will hit 72 and the basement (because there's a 20 ft long exposed copper radiant tube) can get a bit warmer that that. All in all, it can make for a pretty miserable winter season.

My idea to address this disparity is to remove the 1 1/4 manifold and convert the 3/8 copper line to 1/2 pex. Home run those back to a few radiant manifolds near the boiler (one for each floor) control those with zone valves and drive it with a delta-p pump like a ALPHA2 (current circ is a 007). Thermostats on each floor would go back to the zone control box, and well...it's fixed? At the worst it couldn't be any worse than it is now, right?

Or am I off base, and I should just suck it up and live with it?

My second issue is that I don't trust my boiler to not poop its pants sometime soon. Outgoing water temp never gets much above 120F and the return water temp is never much above 110F - the manual explicitly states that return temp should be 130F or bad things happen. Hi limit on the aquastat is set to 150F, btw. Last service tech said it looked to be in good shape...I mean, it's not leaking, but I have doubts about its continued existence at this point.

So the thought to address that would be a...new boiler, of course. Something fancy and hi-tech because I enjoy being without heat for 3 days while parts are flown in from somewhere. Seriously though, I am thinking about a mod-con to replace the CI beast on the floor. I'm wondering if it would make sense to do all these changes at once, since well I'll be ankle deep in whatever mess I make by doing the pex home runs. Oh, and somewhere in there an indirect hot water tank might be a good idea, too. Our home depot special HW tank is ~12 years old and I can't get the anode out (even though I removed it when new and put anti-seize on the threads).

Happy to hear anyone's thoughts, ideas or biting criticisms.

John

bburd

Some pictures of the boiler, the piping around it and the existing manifold you can see would be helpful.

There should be balancing valves at one of the existing manifolds. That is the main point of having manifolds. Unfortunately they are often on the returns, but I’ll bet you can find them if you look hard enough. They should not be buried behind plaster. Perhaps look in the attic? There may be air bleeders up there among other things.

I would look awfully hard before doing the extensive repiping that you propose.

The basement zone should be very easy to zone by conventional methods since you can easily get at the piping. If overheating is the main problem, thermostatic radiator valves may solve it at lower cost. 

EdTheHeaterMan

Since you are getting enough heat from the 3/8" radiant at the 120° boiler temperature, there should be no problem zoning the system. You can do all the designing and zoning using the supply side piping that you can see. As long as you can determine what 3/8 copper is the first floor and what 3/8 copper is the second floor you will be able to set up 4 zones.

Zone 1 = Indirect DHW
Zone 2 = Baseboard
Zone 3 = New manifold for 1st floor radiant
Zone 4 = New manifold for 2nd floor radiant

The hidden return manifolds are already connected to the 1-1/4" return that comes back to the boiler room. That is where you can get the mixing valve Cold temperature water for the lower temperature radiant zones.



This is just an example of what will work if you can't find the hidden manifolds on the return.
There will need to be some purge valves added and there may be more exotic temperature controllers if you are into that stuff. But this is a down and dirty, simple zoning design that will work.

Yours Truly,
Mr.Ed

PS it will work on a cast iron boiler or a Mod Con. The near boiler piping just needs to be adjusted for the ModCon.

jad3675

Thanks Mr.Ed, I appreciate it - and that's what I was thinking of, too.

bburd - thanks too - here are the pics you requested.
So, ha, the manifolds aren't exactly hidden - just out-of-sight, out-of-mind. I hadn't thought about it since I installed that ducted mini-split.

Here's the manifold for the 1st floor return - in the knee-wall space in the second floor.


The manifold for the 2nd floor is in the peak of the roof. Access is provided by a 8"x8" hatch in the corner of a closet. It has an air-bleed at the highest point. I'm not sure how it would every get serviced.


I don't see balancing valves anywhere, though.

Supply Manifold in the basement - well, part of it. It's more of the same for about 20 feet.



The boiler and the near piping. I'll admit, I'm embarrassed by this pic. Don't judge too harshly.


I'm slightly confused by the expansion tank being on the supply side - it wouldn't appear to be near the PONPC, right?

John

EdTheHeaterMan

The place where the expansion tank connects to the system IS the PONPC. "The point of no pressure change is where the expansion tank connects into the system. This is because the air in the compression tank must follow gas laws: a change in air pressure must be followed by a change in air volume. ... Pump operation cannot increase or decrease system water volume, since water is incompressible". This is a Quote from a paper available to read here: https://www.industrialcontrolsonline.com/training/online/how-avoid-problems-your-hydronic-system-pumps#:~:text=The point of no pressure,a change in air volume.&text=Pump operation cannot increase or,volume, since water is incompressible.

The paper has information first identified by Gil Carson in the mid 20th century.
Since there are 2 expansion tanks on your system, One in the knee wall and one near the boiler in the basement. You don't really have a point of no pressure change. Here is why.

This illustration assumes a lot of things being equal. As pressure-drops change due to pipe size, location of the components, and elevation of components, the pressure differences in the two tanks will vary. But the constant is that water can not be compressed, and the pump can not add or remove water from the closed system. That said, if water leaves one tank, the other tank water volume will increase by the same amount. I think @hot_rod would like this illustration

You may want to eliminate one of those tanks when designing your new system. Since we can not always predict what the effect will be in every situation, I would eliminate the tank in the attic by installing a valve and closing the valve. That way if there are unforeseen problems, you can just open the valve to see if that tank resolves the problem.

It's all in the science. Those are Laws that no one can break.

Yours truly,
Mr.Ed

EdTheHeaterMan

I'm sure that someone will point out the fact that your circulator pump is in the wrong position, and several other items inconsistent with proper industry norms and codes. My fav is the garden hose wrapped around the DHW expansion tank. How close is it to the vent pipe? Has one ever melted from contact with that high-temperature vent?

jad3675

EdTheHeaterMan said:

I'm sure that someone will point out the fact that your circulator pump is in the wrong position, and several other items inconsistent with proper industry norms and codes. My fav is the garden hose wrapped around the DHW expansion tank. How close is it to the vent pipe? Has one ever melted from contact with that high-temperature vent?

Ha. I'll take credit for the garden hose that I use to drain the DHW tank. It's a good foot or so away from the flue. No chance of it melting.

As for the circ placement - I can't take credit for that. What else jumps out at you as done incorrectly? House is from '51 and I assume back in 2000 they just did a chop and drop when they put in the new boiler.

Thanks for the illustration of PONPC - I appreciate the explanation.

John

bburd

Those ball valves with the yellow handles on your last manifold pic can be used to throttle zones that are overheating. They function as balancing valves. 

hot_rod

Amazing that the cast boiler has lasted 21 years running 120 supply temperature If in fact you are getting plenty of heat at those operating conditions a mod con, especially on outdoor reset would be very efficient.

jad3675

bburd said:

Those ball valves with the yellow handles on your last manifold pic can be used to throttle zones that are overheating. They function as balancing valves. 

Yeah, I replaced the ancient gate valves with those to do exactly that - and it works - kinda. Two problems - the pipes get noisy (you hear running water in the ceilings) and it requires a bit too much manual adjustment. House is a cape cod with a lot of roof. If the handles are adjusted to keep the temp manageable on a sunny day, those same handle positions don't cut it on an overcast day.

And now I feel dumb for not realizing they are balance valves.

hot_rod said:

Amazing that the cast boiler has lasted 21 years running 120 supply temperature If in fact you are getting plenty of heat at those operating conditions a mod con, especially on outdoor reset would be very efficient.

Any idea why the supply temp would be so low? The boiler can't be undersized - it's 110k and the heat load calcs I did for the house show half that is really needed. Years ago the driver for the circ on the aquastat died - I had 190F supply water at the boiler at that point and the 2nd floor ceilings were toasty. Could it be the taco 007 is moving the water to quickly? 

John