Sizing for upgrading steam boiler

Kjmass1

I currently have a 1 pipe 192k/152k Penco Steam boiler. MassSave had it dated back to 1970. It works fine. I'm trying to see if it makes sense to upgrade and downsize my boiler to reduce my bills and carbon footprint. MassSave rebate is $1800.

After some rehab, we took out a couple radiators/added splits, so my current EDR is 303 sq ft (not adding any pickup).

I believe that would put me with the IN-5 140K for 360 sqft of steam. On paper 27% less fuel, plus jacket improvements, etc which should be significant.

Considering pickup is included in IBR, is there any wiggle room to go even further down to the IN-4 105k for 271 sqft of steam? On paper a 45% fuel reduction. I used 1200 therms last year for heating, so the savings could be significant.

There aren't too many times the radiators are ever filled 100%, outside of a setback. I pulled some data and on 3 consecutive 8-15 F degree days, I averaged 18 cycles of 22 minutes each per day. Since the 99% design temp in Boston is 8 degrees, wouldn't this boiler have enough steam to keep up 99% of the time, especially with pickup losses being so low as the unit is actually more efficient the more it runs? It should be able to produce at least 300 sqft of steam, no? What's the worst case scenario, that it just cycles under pressure? Could I add a vaporstat so it runs on less pressure?

We also have 30k worth of mini split heat if we really needed it as a backup.

My radiators should produce almost 77000 BTU/hr, my heat loss is nowhere near that, at most 50K including my unfinished basement losses. New windows, spray foam insulation in rafters, densepack in walls.

Just trying to think outside of the box here.

Thanks,
Kevin

ratio

I'll defer to the stream guys about that side of things (but I'm on the side of lesser is probably fine), but don't depend on heat pumps for backup. They're great during the swing seasons, but when you need them the most is when they're at the most disadvantaged.

JUGHNE

How well is your steam piping insulated? Supply and return.
Major concern with pick up factor.
Probably very little or no overnight setbacks then?

Do you have only 1 outside mini unit?
If that falls down for some reason would that area of the house still get some steam heat?
Mini's will heat down to a pretty low temp....but how much heat is always a concern.

IIWM, I would go for your plan.
If the house chills it is time to run the oven thru a self-clean cycle or bake cookies.

Kjmass1

I’ve insulated 95% of the pipes except the 90’s, and header.

No setbacks except a long weekend away. Spouse works from home so we keep it at 71 all winter.

I have 2x 24k condensers with 4 heads. 12k heads on first and second floors, 7k in the master, and another 12k in the finished attic which we turn on as needed.

They aren’t the low heating versions, but should be able to provide meaningful heat into the single digits.

Forget the splits for a minute- how would my steam system perform at a 300 EDR demand but 271 edr boiler? I did add some big gorton main vents in order to vent mains fast, but rads slow.

JUGHNE

Another consideration as you down size the boiler is water capacity of the new boilers compared to the old one.
As the water boils away would the new water line drop enough to bring on the water fill?
Do you have any wet returns that could be sluggish for condensate to return?

I did read that some installers would get the next size boiler for the extra water capacity and then down fire the burners with smaller gas orifices and/or reduced manifold pressure.
That was an old school method. Don't know if still a good idea.

Some here may know/comment.

Kjmass1

Good point about the low water fill. Not sure about the returns- nothing out of the ordinary that I know of.

This article is what gave me the idea:
https://forum.heatinghelp.com/discussion/159686/taking-another-look-at-steam-boiler-sizing-methods/p1

Can anyone recommend an installer/resource in the Boston area? If not I’ll hit the contractor list.

SeymourCates

The article makes some valid points.

There is an extreme reluctance to proceed in this direction because considerable effort is required on the part of the installer to carefully balance the system. This requires patience and time and a contractor doesn't possess either one.

If you have the patience, consider the Peerless 63-03L boiler. It precisely matches your radiation and will definitely require the small vents referenced in the article. That being said, it still offers a net output of 73K which is far more than your heatloss.

The boiler contains 9.3 gallons of water which is plenty for your system.

And finally, if it all goes south on you (or the installer), it's the exact same boiler as the 63-03. You can always raise its output to anything up to 98K if absolutely necessary.

I'm not a champion of Burnham steam boilers unless you consider 10 years as acceptable longevity. Once you have to replace it, any savings garnered from the new boiler are totally gone.

New England SteamWorks

I also like the Peerless 63 series boilers