Need boiler recommendations

Tony_D

We have a 1.6M BTU natural gas hot water boiler servicing 28 units of 1,000 sf each. Installed in 1967, it just stopped working for the first time ever. A few years ago, a boiler guy recommended we install two boilers if we ever need to replace. He also suggested we use them to heat our hot water instead of the two 96 gal heaters we use now (one of which is very new).

We are in southeast Michigan.

Does anyone have an opinion on the two boiler thing? Best brand and/or models? How about replacing the HW tanks with tanks on the boiler(s)?

Thanks so much for any input!

jesmed1

First thing to do is to find out what size boiler(s) you really need. With 28,000 sq ft, your 1.6MBH boiler is probably something like double the size you need.

Unfortunately it may be difficult to get an accurate number for yor building's heat loss, because you've been using gas (I assume) for both hot water and heating, so your previous gas bills can't easily be used to caculate the building's design heating load.

Since you have one boiler heating 28 units, I'm assuming it's one big box-type building, and in southeast Michigan you might be looking at 25-30 BTU/sq ft design heat load, which would put you around 700-840MBH. But that's just a ballpark guess.

So you may get stuck replacing with another 1.6MBH unit unless you can get someone to do a design heating load calculation based on building dimensions, materials, insulation, window sizes, etc. Since this is a large boiler that is going to be a costly project, I would definitely pay someone to do a design heating load calculation. There are pros here who can do that for you if you can provide the input data.

Meanwhile you might find this video from Dan Holohan helpful. He ends up installing two boilers in this mansion partly because of the sizing uncertainty, and his logic may apply to your situation too. He set these two boilers up so that only one would run in milder weather, and the second would kick in during colder weather. He later found that most of the time, only one of the new boilers boiler needed to run, proving that his argument to the homeowner that the existing boilers had been massively oversized was correct.

https://heatinghelp.com/systems-help-center/a-cautionary-tale-for-replacing-boilers-on-hot-water-heating-systems/

Tony_D

Thanks for that. It actually services 3 buildings (two with 8 units, one with 12). Two floors each. 7 hallways but no radiators in the halls.

jesmed1

Tony_D said:

Thanks for that. It actually services 3 buildings (two with 8 units, one with 12). Two floors each. 7 hallways but no radiators in the halls.

That complicates the heat load calculations, but it still can be done for 3 separate buildings. That's the first thing you should do. Hopefully a pro here will make some suggestions.

Hot_water_fan

With two boilers, you can get two of different sizes. So smaller one handles cool temperatures, the larger handles colder temps, and combined handles the coldest temps. 

An indirect is fine but marginal. If you have a new water heater that’s sufficient now, wait until that goes. 

WMno57

Tony_D said:

We are in southeast Michigan.

Two Mod-Con boilers could save you a lot money on your gas bill. Sizing doesn't have to be spot on with a Mod-Con because they modulate their output. Your old gas bills can also help with sizing. Not a good time of year to have a boiler die for 28 units.
A boiler with an indirect will make hot water cheaper than a dedicated water heater, because boilers are more efficient.
@GGross and @mattmia2 may be able to help you.

Intplm.

The two-boiler idea is great for many reasons.
First, the two new boilers will fit in the building. This is sometimes overlooked and very important. Your original boiler from 1967 is surely very large compared to the two new ones that will be installed.
Two boilers also can be used as an on-demand requirement.
One can be swapped manually or automatically when demand calls for it. And both can be used when heat demand is at its highest.
I'm also beginning to lean toward separate water heating, rather than relying on a boilers heat source to heat domestic hot water.
If the heat goes out or vice-versa you will still have one working without everything out all at once.

Hot_water_fan

A boiler with an indirect will make hot water cheaper than a dedicated water heater, because boilers are more efficient.

Depends! Plenty of stand-alone tanks exceed the efficiency of an indirect. 

Now, your cheapest Home Depot gas tank will not, but manufacturers make high efficiency gas tanks. 

jesmed1

If you can't get a pro to do a design heating load calculation, you can do it yourself. There are a number of free online heat loss calculators. I used this one to calculate the heat load for my 4800 sq ft 4-unit condo building in the Boston area, and found the results agreed well with calculations from other methods, including using actual oil consumption. So if you make reasonable guesstimates as to R-values, you can get pretty accurate numbers. You can Google a table of R-values for common building materials and insulation types.

https://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

Steamhead

@Tony_D , can the present boiler be repaired? What went wrong with it?

Tony_D

Steamhead said:

@Tony_D , can the present boiler be repaired? What went wrong with it?

Just found out it was repaired but the details have not been forwarded to me yet. This is at my Mom's CoOp apartment complex at which I'm a board member and no longer live on site. I'll update when I find out what's what!

offdutytech

You should check with DTE or Consumers energy whichever supplies your gas. Both have incentive programs for commercial buildings to move to high e equipment like a mod con boiler. Two smaller boilers cascaded with controls is pretty standard for that type of setup. You will find a heavy Lochinvar presence in the area on the commercial side of things and it helps they have a distribution center in Plymouth. Viessman offers a nice package as well, but not many commercial companies are using them in this area. Your scope of work is a bit too large for our company, but there several others in the Detroit area that handle that a scope of work. 

MaxMercy

WMno57 said:

Two Mod-Con boilers could save you a lot money on your gas bill.

While that's certainly true, this CO-OP is used to having a very reliable system for decades, even if it's inefficient (is it?). In the back of my mind, I'm thinking they need to be sure they have a stable company locally who can properly install the new mod/cons, service it if it quits (the controls are more complicated), and have replacement parts available - something they will need more than for a "dumb' boiler. On the plus side is that with two boilers, the chances of both quitting at any given time is quite low.

They will also need to consider having to replace one or both in 15 years or less.

EBEBRATT-Ed

@Tony_D

I would talk with @offdutytech he does excellent work and posted above that the job is large for his company. He can probably give you some good recommendations on who you might use.

tim smith

1) What is your annual therm usage, check with your gas utility. 2) hat is your maximum usage in coldest month they can tell you that too. Gives you real world sizing initially. I am a big fan of the Lochinvar boilers. In your size range probably 2 FTXL boilers, may be as small as 2 FTXL 400s or 2 - FTXL 650s. Doubt any more than that. Their indirect hw tanks are great also, maybe 2 lochinvar SIT119s if you don't require double wall heat x or ASME for the tanks. Done many in apt bldgs and all are happy campers. Not many parts have had to replace on Lochinvar, very few. Again, more maintenance than a cast iron and life span probably half of what a cast iron will be. Food for thought.
Tim