Rather than worry about brands at this stage, you should be
more concerned with who’s the right company to design and do this job right. It
looks like you have at least 5-zones and a gas DHW heater.

Find the right people for an installation that will be
efficient, save energy and clean up your mechanical room. You might explore a
gas boiler that will also heat an indirect DHW tank.

Do you have any asbestos issues that will need to be dealt
with? Do you have low temperature cast iron radiators running at about 140˚F?

You want a mechanical room that should look like a piece of
modern industrial art, with controls and labeling to match – not a ‘Das Boot’ U-Boat
Torpedo Compartment!

Dive! Dive!

IMPO

SR

Not a professional, but I'm from the twin cities and those I know with these old boilers would never want to retire them. Do you have the boiler regularly serviced, and the mechanic told you it was failing? My bff just sold a house with a boiler over a 100 year old and with regular servicing shouldn't need replacing anytime soon.

Oh fsq4cw, I feel that your negative comments about the boiler room are off base. Those big red, massive B&G pumps are beautiful to behold. It is hard to believe that they are still there. Most systems would have had some or all of them all swapped out for some tiny Tacos by now. There are nice, robust-looking isolation valves on both sides of them and a drain valve on each loop. The circulators are all numbered. It looks like all the controllers are neatly lined up neatly on a utilitarian panel and wired via some very tidy conduit. (Unfortunately the pumps are probably so oversized that they use too much electricity to be practical. One of them might be big enough to pump all 5 zones.)

OP, you will almost certainly be asked to drop a modern, efficient modulating/condensing (mod con) boiler into your existing heating system. If you can, you should do it, but it can be tricky. It is best that you have a plan even before you start getting bids. Someone on the project must know what they are doing. It may be impossible without major modifications, but you might be lucky. That might mean that you end up installing a less efficient boiler just because you can't take advantage of the more efficient modcons. If the modcon won't run right. They short-cycle and run too hot. That causes the efficiency to drop and might cause operation problems leading to failures. They cost more too. They are really best running nearly continuously from the time the weather gets cool in the fall until you don't need them any more in the spring.

Beware suggestions for installing combination (heat and instant hot water) boilers. They make it even more difficult to fit a boiler. Is there a local energy efficiency program that might pay for or subsidize an evaluation of your home? It could be utility based or local/state government based. It would be handy to know the heat loss for the building. Along with that, fuel use records and local temperature records can provide an even better estimate of the heating needs plugging in the existing boiler efficiency. Heating degree days should be available from local weather stations. Ideally, you will have radiation measurements and heat loss estimates for each room. This is a gas boiler? Can you run a plastic vent outside the home near the boiler in its existing location?

Here is a brief summary for retrofitting a condensing/modulating boiler. They are the most efficient. The return water cools the flue gas condensing water and recovering the heat. The cooler the return water can be, the more efficiently they run. If the return water gets too warm, more and more heat goes out the vent. Your current system has return water of at least 160F and the boiler is probably always hot. With a modcon to get into the least efficient range the water has to be below 130 and closer to 100 is better. You don't, however, need to attain that for the entire heating season to make it worthwhile. Water temperature can be much lower and still heat the home well in more temperate weather.

Some things that work in favor of retrofitting a condensing boiler into a home of that vintage:

Lots of "excess" radiation still in place after the home is retrofitted with good windows and insulation and well air-sealed allows the radiation to transfer enough heat with at low temperatures.

Cast iron and sub-floor radiant heat works better at lower water temperatures (as opposed to aluminum fin convectors and hydrocoils.

Big zones help too. Some older houses were originally cut up into many zones starting in the 70s as an attempt to cut fuel costs. With modcons, the problem is having a boiler that will heat the whole 3,600 square and turn down enough not to short cycle with one zone calling for heat. Sometimes zones are re-combined and sometimes it is a good idea. If all else fails and you want a mod-con, a buffer tank can be used to prevent short cycling. That way the boiler can spend more time in low-fire (more efficient) as well. Keep in mind that zones do not save that much energy if the house is well-insulated and sealed. Heat transfer from room to room is much faster than from inside to out under these conditions.

Under your conditions, if low water temps cannot be reached, but short-cycling is still a problem, a Versa-hydro or Versa-Flame boiler from HTP might be a good modcon to consider. It has a built in buffer and can provide domestic hot water without an indirect tank. Under many conditions, maybe even universally, with condensing boilers, some re-piping is needed to prevent water that is too cold from entering the boiler. (You need a primary-secondary system. Envision your existing zones all feeding from and dumping into an inboard loop, with its own circulator that runs directly into the boiler.) These HTP boilers can be dropped in, I think, with none of that which can save installation costs. You might not even have to change your existing header. You won't even have to consider changing around your zones that way. Significantly, less or no skill is required in design of a different system to make good use of that unique modcon boiler. The big beautiful B&G pumps might have to go, though. I hope that I am wrong, however, slowing down the water flow is one way to reduce return temperature and those things can probably move 150 gpm between them.

Ionized_­gw:

On the one hand – I agree with you! It is a beautiful
system, a piece of plumbing/heating history. I marvel at them when I see them.
I hate to remove these legacy systems but they are not efficient and the owners
want to save energy.

On the other hand I doubt anything installed today will last
as long.

SR

@ionized: I'm an engineer. I replaced the old B&G pumps about 15 years ago, added the full flow ball valves. These pumps are very quiet. I also wired them with quick disconnect plugs.

I found a boiler guy - going to get a 140,000 BTU / 85% Burnham boiler. We are going to support all the piping, and keep the return / supply piping.

I'll replace the WH, and keep everything simple.

@fsq4cw: On the other hand I doubt anything installed today will last
as long.

That's what I wonder about. My Weil McLain boiler will hit the half century mark in 2020. Outside of the pumps, the only thing replaced on it was the thermocouple - once - and I could pick that up at the local hardware store. The two zones are controlled by ancient mercury bulb round Honeywells.

Efficiency is great and all, but the cost of service is not. There are plenty of stories online on how the boiler or furnace 'mother board' had to be replaced at a hefty price. And then there's the fancy electronic thermostat that failed off while the family went on a 1 week vacation to Florida. Upon returning they found frozen waterfalls in the house because of frozen pipes. Or, better yet, the family who kept their summer vacation house at 50 degrees and the thermostat failed on. The January desert in the house warped all the engineered hardwood floors requiring them to be replaced.

Of course, I don't have statistics. Don't know how one-off the online reports are.

Re: wishiwereintheup

This is a calculation you have to make. Based on any number of factors, replacement may not always be the best decision.

IMPO

SR

How was the the 140,000 BTU size determined?

"How was the 140,000 BTU determined?"

I got 3 estimates - this can be a story in itself:

First company, installs boilers for 30 years. A real boiler guy came out. Liked the pumps / layout. Looked at original boiler that was 175,000 BTU. By the size of the house ( 3,600 sq/ft), in Minnesota... we decided on 140,000 BTU (110 would be too small, and we didn't think I needed 170,000 in a new, more efficient boiler.) I thought his price to replace and install was $7,500 - which I thought was reasonable.

Second company, did a complete measurement of my home, took into account age, structure (stone), etc. After 1 1/2 hrs of calculation he came up with a 140,000 BTU Slantfin boiler. His price was $12,500 - which I considered high. To get a more efficient boiler was $16,000. But hold on to your hat - a high efficiency with DHW was a whopping $21,500.

Third company - advertises heavily - 'Comfort Consultant' shows up. Takes some pictures of my boiler. Didn't ask any questions, gave us a card, as said he would 'get back to us soon'. Been almost a week. No way would I want them to do this job.

About the sizing of the boiler - calculations show 140,000 BTU will keep my two story, 3,600 sq/ft home, at 72 deg with an outside temp of -25.

Oversizing boilers and furnaces has been very common and maybe still is. On the other hand, maybe improvements to your structure has knocked off a few thousand btu (but have there been additions?). I am surprised that no one has yet measured your emitter capacity. That measure is mandatory for a boiler replacement IMHO, just as or more important than total heat loss for the home. If emitter capacity does not equal or exceed the boiler capacity, you will short-cycle, no question. That goes more for a low mass boiler than a high mass. If your replacement does not have the buffer capacity that the old boiler does, it could short cycle even if the existing boiler does not.

If I had a house of the right size with a high-mass boiler system, I'd seriously consider dropping in a Westinghouse WGR060NG076. It is designed similarly to the HTP Versa-s, and a twin to their Pioneer water heaters. It needs only a 2" pipe for venting flue gas. It has a 3:1 turndown ratio (rather than 5:1 for the Versa-s and no heat exchanger to make them combi boilers). They are high mass. Most of that mass is in water and the boilers/water heaters use the natural temperature polarization of the heated water as what appears to be a very effective heat exchanger. Pretty ingenuous IMHO. You'd need two of them, but if you did install them, you'd have mid to high efficiency for less than $5000 in boiler costs, you could install them yourself, and you might be able to wrangle a 6:1 turndown ratio, on a manual basis if not automatic. I don't know, however, if one at a time, they could provide the GPM that you need.

You know, in engineering circles, there has been serious consideration of installation of small, high-efficiency, modulating boilers sistered to existing high output, lower efficiency boilers. The idea is that the old behemoths will take over during a few hours a year near the design temperature while the modulating boilers run at very high efficiency meeting most of the heating needs. Maintaining, and possibly, replacing, two boilers adds a lot of complexity and cost. Balancing that, you have some redundancy.

You are quoting input btu for dem boilers?

FYI, two years ago all including removal of an oil tank which, I understand) is not considered to be a big deal :

Baxi Luna Duo Tec (19-113 kBTU output) ~$9000

Weill McClain GV90+ 4 (97 K output) included indirect tank ~$10000

Same thing from another contractor $8165

Rinnai E75CN (75 k output) $8,950

Utica UB90-075 $9200 including indirect tank

Triangle tube (Excellence 110) with built in (tiny) tank $9500

Navien Modcon ((NCB180) $9500

A wide variety of boilers were offered from different contractors at about the same price. Two are mid efficiency ~90% (Weill McClain and Utica) while the others are in the mid 90s if they are installed and work properly. That installed and operating properly was the sticking point. I did not think that the lightweight Modcons would work well replacing the ole case iron Sunny Day. This was going to run three zones of 16, 11 and 12 kbtu aluminum fin-tube convectors.

Now that I think about it, maybe the Triangle Tube would if the heat was plumbed to the circuit with the small tank using it as a buffer. If I had to start over, I think I'd start with the Westinghouse and install a second one for DHW.

@ionized: I don't thing it's really that difficult. I don't know why you are rambling on.

What is it that you don't understand?