Boiler Plumbing Advice

patrickoneal

I'm replacing an oversized cast iron hot water boiler with a Navien 80k btu modcon. I have a 40 gallon indirect tank that I will be keeping and using with the new boiler. I've got space in my garage to do so, so I want to pre-fab as much of the plumbing as I can before I switch out the boiler.

I've studied the manual and I have acquired the prefabricated manifold to go with the boiler. The boiler will be mounted on the wall in my attached garage, and the supply and return piping all emerges from the wall near the floor. I've attached a quick and dirty sketch of the proposed layout of my components, and I have a few questions if anyone would be kind enough to provide some advice.

1. In an effort to conserve wall space I have a lot of elbows to get up to the expansion tank and air separator before turning back down and around to the zone pumps. I'm aware that I have to have 4 diameters of straight pipe after the closely spaced tees before the first elbow. Other than that rule, is there any problem with taking such a circuitous route to the zone pumps?

2. The main pipe with the primary tees is 1 1/2" copper(I've labeled it "D"). Both sets of my supply and return pipes are 3/4" copper. Should I maintain 1 1/2" pipe through the air separator all the way to each of the two zone pumps? Or is a smaller size acceptable?

3. Should I maintain 1 1/2" copper pipe up to the point that my zone return pipes connect?

4. I'm aware of the importance of the spacing of the primary loop tees, and the requirement for minimum amounts of straight pipe on each side of the tees. I haven't read anything about spacing out other components. Is there any required spacing between the zone pumps or should I just put them far enough apart to comfortably access each pump for maintenance and replacement?

5. As in question #4, should I space out my zone return pipe connections?

Thank you for any advice you may have for me.

GroundUp

Nothing wrong with that layout at all. A single 1" main will feed more than two 3/4" branches can use, so no need to keep the 1-1/2" so long as the 3/4" is adequate for the zones. The air eliminator doesn't need to be at a high point, it'll do its job anywhere on the supply side if that helps save any space. Spacing of the zone tees can be as tight as you like with no ill effects- just make sure those new pumps have an IFC to keep one from backfeeding the other.

Zman

Unless you have high flow requirements on the system side, you should be able the pipe it all in 1".
You will want to make sure you have check valves on the circs.
Give yourself plenty of ways to purge the system.
Air separators also tend to act as dirt separators. Your expansion tank will live longer if you pipe a blowdown valve under the separator and pipe the expansion tank off to the side.

patrickoneal

GroundUp and Zman, thank you so much for your replies.

Navien mentions the IFCs on the zone pumps and seems to recommend one on the boiler pump as well. I was planning to make sure all four pumps have check valves.

As far as stepping the piping down to 1", can I do that at the ends of the 1 1/2" pipe on the manifold? I've attached a photograph of it. Or should I extend the pipes prior to reducing it? I know I need some straight pipe after each tee, and I can't see how reducing it there would hurt anything.

Zman

It's probably a good idea to keep the recommended diameters before reducing. I think it will work either way.

patrickoneal

Thanks again Zman. The 4x and 8x measurements of straight pipe were something I found on google. Looking closer, it looks like a lot of manufacturers recommend 6x diameters on both sides. I think they're talking nominal rather than actual diameter. Navien is silent on the matter in their manual, but if it's needed I don't want to have to go back and redo a bunch of plumbing.

Zman

If you get it close to those numbers, you will be good. In many installations, there just isn't room. Just do the best you can.

mattmia2

You will want to put a ball valve somewhere between the boiler and the fill valve and a drain before the ball valve (or a pre made purge station)so you can block flow in the boiler loop and force water from the fill valve, out through the system loops one at a time, and out the drain to purge the system loops.

mattmia2

patrickoneal said:

Thanks again Zman. The 4x and 8x measurements of straight pipe were something I found on google. Looking closer, it looks like a lot of manufacturers recommend 6x diameters on both sides. I think they're talking nominal rather than actual diameter. Navien is silent on the matter in their manual, but if it's needed I don't want to have to go back and redo a bunch of plumbing.

It is a lot more important in much larger industrial systems or systems where the flow is approaching the maximum recommended for the pipe.

patrickoneal

mattmia2 said:

You will want to put a ball valve somewhere between the boiler and the fill valve and a drain before the ball valve (or a pre made purge station)so you can block flow in the boiler loop and force water from the fill valve, out through the system loops one at a time, and out the drain to purge the system loops.

Thank you for the advice.

I think I can picture what you mean, but I'm not totally sure.

The prefabbed manifold has some ball valves and two drains on it, and I was planning to use the Webstone circulator pump flange kits that have a built-in drain valve at each of the two zone pumps and the dhw tank pump.

I was also planning to use Webstone "T-flow" ball valves with drains at each of the three returns.

I didn't show all those valves on my "quick and dirty" drawing above.

That seems adequate to purge all the loops? Or might I need something more?