Despite brand new gigantic biasi, certain things not getting enough heat

hotwired

We've always had a minor issue getting one apartment to get up to snuff temperature wise. Context: It's a HUGE building we bought in 2012, 7,600 square feet, 7 units. It had two boilers, one for the left half of bldg, one for right. We weatherized the entire building via a state energy program here in Maine and replaced the two with a 6 section pensotti type boiler. It did just fine, but when it hit zero or below, our biggest apartment on first floor would struggle to get above 63. So it was only for about a week each winter we had to tail chase and try to figure it out. Finally after 8 years, our heating company managed to arrive right when it was having a problem. They found the boiler really wasn't getting up to temp due to the load. It was only when everyone was home, taking showers, getting ready for work, heat still up high, etc. So we did a quick 10K swap out and replaced the pensotti with a behemoth Biasi which seemed to do the trick, but lo and behold it's starting again, only not as bad. Now its' just the living room of the apartment ... below zero, they have to use space heater to be cozy, as the temp won't get above 66. So not as bad but still....grrrr....we then heard from another tenant, who'd never complained, that during these cold snaps, their apt. struggled to stay at 66 too, which was a surprise.

Now for the living room in question, there are carpets, and the baseboard ARE too low, so that restricts the convection. So I cut out the carpet and that left a CAVERN of nice space under them. The baseboards are hot, but just not heating the room really well. Yes, there's big bay windows, it's a 20x24 foot room. The "weaknesses" here are wall insulation. The bldg is more than 100 years old. But everything else checks out. The place is air sealed to beat the band. foamed basement, capped attic, new vinyl replacement windows (6' tall) throughout, etc. I do have a friend and associate who's a licensed weatherization guy so he's going to pull away from a job soon and do an infra red scan and see if there's any outsized heat loss, but ... does anyone have any thoughts?

So...oil heat, baseboard, indirect hot water, full air sealed and weatherized, though old, so questionable insulation in walls. Baseboards too close to floor, but partiall rectified by removing carpet, allowing substantial space.

Thanks even for any bumps in the right direction...even a crazy idea or two welcomed!!

Robert_25

Unless your old boiler was unable to reach the target water temperature (commonly 180F) it was not undersized.

If only a handful of rooms are cold you likely have flow balance issues, insufficient radiator, or both.

Is each apartment on its own zone?

hotwired

Each apt. is on it's own zone, using zone valves (there are 2 circulators then zone valves from there vs. each apt. having its own circulator pump.

Robert_25

When most of the zone valves are open (like when it is -20) the water will take the easiest path. If your system is not balanced, the longest loops will get the least amount of flow compared to the others.

1. Do a heat loss calculation of the cold apartments using the Slant-Fin Hydronic Explorer app: https://www.slantfin.com/slantfin-heat-loss-calculator/ This will tell you if the amount of radiation installed is adequate.
2. Take inventory of the pipe size of each zone, and the length of the longest zone.
3. See what the make and model of your circulators are.

Kickstand55

Go with what Robert_25 said. Measure baseboard "element" in each room, not the enclosure. Make sure all piping near the boiler and heating pipes leading to and from the baseboards are well insulated, especially going through cold basements. No long 70' runs, (See posting somewhere in this site). Maybe need to switch out the zone valves to circulators, Primary Secondary Piping, and other mods.
I would have used 2 smaller properly sized boilers with lead/lag controls with Primary Secondary piping, circulators correctly chosen for each zone.
Also, without pictures, we can only imagine what a mess you're in. We like pictures.