Manufacturer specs- mandatory or recommended?

Why do the manufacturers put it in writing if there not to be followed.

The installer is wrong!

Hope you put it on a Credit Card, I’d dispute the charges until it’s corrected.

like you said “Recommended Minimum “

Did they follow that?

NO

You can let @New England SteamWorks answer that himself but i think the manual has some language that allows other industry accepted methods. Because it has the drop header to help the steam and water separate over the long path and turns the 2" is very likely fine for the header.

Your returns are above the water line anyhow until they get to the boiler so the only place that the water could leak out of the boiler is at the piping near the boiler. The lower connection to the hartford loop just means there is a small amount more piping that could leak and allow the water to run out of the boiler. The lwco ("safegard") is there to stop the boiler from firing if the water gets low anyhow so on modern automatically fired boilers the hartford loop is redundancy.

OK here is the scoop on Minimum Recommended Pipe Size. You have a diagram that shows that you only need one riser that is 2-1/2" diameter that transitions with a 90° elbow into a 2-1/2" header. The end of the header then transitions into a 1-1/2" equalizer drop where the wet returns connects via a Wye fitting or a short nipple before it connects to the boiler return opening at the bottom. That Wye fitting has a minimum 2" below the water line specification.

Since your contractor did a double 2" riser, that is more that the minimum requirement. The Wye fitting is at 3" below the water line, so that is more than the minimum requirement. the fact that you have a drop header will better facilitate dry steam to the system. the only shortcoming I can see is the short section of Header where it is common to both the double boiler risers and the double system risers may have an increased velocity that may cause some water to find its way into the steam mains. Only time will tell if that actually is a problem. After the system is skimmed and the water conditioned for pH, I doubt that you will have any problem.

If at all possible, I would hold back $500.00 from the final payment (if that is possible) to insure that the system operates properly without major banging noise. (some expansion noise is going to happen on any heating system) If you get major banging that can not otherwise be explained that the header should be increased to 2-1/2" but I don't see that being a problem.

Otherwise you have an excellent system. Give it a month to see if there are any problems that skimming does not solve. Follow @ethicalpaul and his YouTube videos for proper boiler care of your new system.

The guy did a fantastic job. Who did the insulation? Perfecto! The manufacturers specs are minimum standards for reliable performance. I'm a big believer in individuality, artistry & freedom of expression. As Ed said, he used both tappings. You got a very nice job! Mad Dog

Nobody mentioned the Vaporstat and the union on it. A very nicely piped boiler.

Perhaps a EG 35 may have worked, but you really need to match the boiler to the connected radiation EDR. I think your contractor nailed it. No noise, no cycling on the pressure limit, home is comfortable …EXCELLENT!!! Your home has too. much radiator. I bet it has something to do with the Spanish Flu. https://www.heatinghelp.com/systems-help-center/boiler-sizing/ This is one of my favorite @DanHolohan stories.