Tankless coil v Condensing Combi Boiler

Coldshoulder

My 7 year old Navien Combi boiler's 3 way valve failed this Spring. Plumber also informed me that he sees a leak from heat exchanger, and due to installing plumber's failure to place isolation valves on the device, now (after 7 years of doing) Navien say they will not warranty the parts. Since the cost for parts and repair is in excess of $6k, I have decided to replace the boiler.

My initial reaction was to stay away from any Combi boilers, since a mere 7 years is very disappointing. However, I have a small closet and 2 plumbers advised that a gas boiler/indirect tank was not possible and recommend that I either replace the boiler with a tankless coil boiler or a combi boiler. Plumber assures me that the tankless coil (Slantfin SFC 199 Combi) will be sufficient for heating and DHW for a 1800 SQ FT HOME with three bathrooms.

On the hand, I am being advised to get a better combi boiler (IBC SFC-199 NG) with proper valves and annual maintenance, which will give me 25 years of service. I am no longer interested in Navien, but I am open to other combi boilers.

Interestingly, one plumber says he could install a mini therm and a small indirect tank in my closet. According to plumber this option will be less maintenance and 15 yr life minimum. However, it is the most expensive estimate.

Any thoughts would be greatly appreciated?

EdTheHeaterMan

That's the problem with some building designs. The mechanicals are an afterthought. Barely enough room for the unit that is installed when built and never enough room for what may be needed to replace it.

If you can get a standard boiler with an indirect in easy access for service location, you should go for it. They will last longer and you don't lose both pieces at the same time when one of the items fails. A tankless coil in a boiler is the least expensive option to install but the most costly to operate. the extra expense for an indirect is usually less expensive in the long term.

So if you are selling the place next year, then the low-cost installation is your best bet. If you are planning on living there for the long term, spend the extra on the indirect. that is what I have and I'm only on my second tank in 34 years. The same boiler for 34 years and I got that used (5 years old) from a house being torn down. Cast iron is King when it comes to lifespan. (it was one of the first Buderus boilers installed in South Jersey back in 1982)

Big Ed_4

For longevity and low maintenance I also would recommend cast iron and an indirect . Lack of room is another issue . Stacked boiler which sits on the indirect may work or pipe the indirect which would sit in another location could be in another .. I really cannot recommend a coil.

If a Combi was my only choice ,the unit that I see with the least amount of issues would be the Bosch . All Combi and condensing boilers have a higher maintenance cost over a cast iron boiler . The Bosch is the easiest to work on with the least amount of issues that I have worked on .

Hot_water_fan

@Coldshoulder The IBC SFC-199 NG has a huge output.
How much gas did you use this past winter? And what's your general location?
A small CI and small indirect might be more appropriate. Depending on your circumstances, a small CI boiler and small electric tank heater might even work.

Coldshoulder

Hot_water_fan said:

@Coldshoulder The IBC SFC-199 NG has a huge output.
How much gas did you use this past winter? And what's your general location?
A small CI and small indirect might be more appropriate. Depending on your circumstances, a small CI boiler and small electric tank heater might even work.

I don't have exact figures for my gas consumption. It was above average this winter with most of the family at home every day all day. Nevertheless the Navien was, if nothing else, efficient. I am in Long Island NY. Not as cold as upstate NY, but we do get some wicked cold here. I also have three bathrooms with in-laws visiting from time-to-time.

Hot_water_fan

Using 4500 HDD, we can estimate the heat loss pretty easily: Depending on where you fall here, you could downsize and still have plenty of capacity for DHW. Might make fitting a small indirect in easier. It'd do well with a modulating boiler or cast iron.

Coldshoulder

Big Ed_4 said:

For longevity and low maintenance I also would recommend cast iron and an indirect . Lack of room is another issue . Stacked boiler which sits on the indirect may work or pipe the indirect which would sit in another location could be in another .. I really cannot recommend a coil.

If a Combi was my only choice ,the unit that I see with the least amount of issues would be the Bosch . All Combi and condensing boilers have a higher maintenance cost over a cast iron boiler . The Bosch is the easiest to work on with the least amount of issues that I have worked on .

Not sure if Bosch is not widely used here, or if the plumbers I have consulted have agreed to work with a certain brand, but they have said they don't install that brand. I'll check the Bosch service providers in my area. Any thoughts on the IBC SFC 199 Combi Boiler?

kcopp

The IBC line is a fav of mine. The 199 output pertains only to the hot water side. The heating side modulates from 20-125K. Still probably more than you need...but not 199k as one could be lead to think.

Big Ed_4

I could say with confidence there are plenty of Bosch Green Stars installed on Long Island ...

Robert O'Brien

Big Ed_4 said:

I could say with confidence there are plenty of Bosch Green Stars installed on Long Island ...

I've done my share!