Boiler Replacement for Apartment building

[Peterx]

We currently have 2 Laars Mighty Therm boilers (400 MBH each) connected in series to heat a 25 unit apartment using aluminum fin radiators throughout. The heat exchanges in both boilers appear to be leaking so we are looking at several options. The boilers are about 18 yrs old so we are not sure replacing the heat exchangers is sensible. If we replace the boilers are first preference, given the cost of a condensing system, would be to install a new hydronic system. I would be interested in your thoughts on whether replacing the heat exchanges makes any sense and if not I assume we would need to get a heat loss study to size a replacement system. Would that be included by people bidding on the replacement or should it be done by a consultant? If the latter any thoughts on cost? Any comments on most reliable replacement boilers? I have seen some concerns expressed about mighty therm 2 and bosch but I don't know if those are isolated experiences.

Thanks for any feedback; we are a small self managed coop apartment so we do not have much experience in this type of decision.

 

[NY_Rob]

If you go with a (qualified) consultant he will come up with a single bid spec that interested HVAC firms would bid on. At that point it would be easy to compare apples to apples between offers.

If you have independent contractors come in and spec out the building on their own you'll get a very different proposal with different equipment and values from each contractor. You would then need someone to interpret the proposals and decide on the one that fits the best.

I would look for a qualified consultant and let him/her advise you/the board on how to proceed. The consultant would also inspect the work in progress from time to time to make sure it's up to bid spec and being installed according to manufacturers recommendations... that's extremely important in HVAC work. Being a third party, he/she would always have your best interests in mind vs. working for the HVAC contractor.

 

[Sponsor]

 

[Dana]

Having 800K of burner for 25 apartment units is an average of 32KBTU of burner per unit. It's unlikely that the design heat load is anywhere near that level (it might be as much as half that if the apartments are pretty big), but if the boilers are serving up domestic hot water as well as space heating the total load could peak that high.

A service life of less than 25 years before leaking indicates there may be a design error in the system, with return water cool enough to sometimes condense on the heat exchangers.

 

[Peterx]

Thanks for the replies guys. The independent consultant idea does make sense to me; does anyone have a ball park idea of what a study like that would typically cost? I think the points about the BTU size and heat exchanger condensation are well taken and I would build those concerns into the study. Given that we are dealing with a lot of radiators and zones this seems to me like a difficult design but I am hoping that it would be pretty straight forward for a qualified consultant.

 

[Dana]

For a project that size a heat load calculation and system design review would probably start around CDN$1500 but probably not more than CDN$5K for an explicit design spelling out every pump and valve, but I really can't say for sure. Every market is different, and there are multiple aspects to commercial building codes and other requirements in B.C. that I have zero familiarity with.

If it's determined that there is enough fin-tube baseboard to be able to operate at condensing temperatures ( <55C boiler output) it may be cheaper to go with modulating condensing equipment, or maybe even a reversible chiller/hydronic heat pump solution rather than just another cast iron or finned water tube boiler.

 

[Peterx]

Thanks Dana; that is very helpful; wish you lived closer.

Cheers
Peter