Working toward the boiler room we had to dodge the domestic water tank that was taking up half of the walkway. The domestic tank was newer and evident that at some point this was added. The contractor didn’t have space to work with, so the tank had to be jammed in and vented into the same chimney as the boiler.

If you look closely at the existing boiler, you can see a black box in front of the vent stack with the water connections cut off. That is a tankless hot water heater. This was the OG “combi” boiler. In its original life, this boiler was heating domestic water indirectly. In the black box there is a ½” copper tube coil that held the domestic water. The boiler would run all the time maintaining 140°F or so transferring heat to the domestic water in the ½” coil. This was not a very efficient way to make domestic water, but was popular on the East Coast in the 1960s and 1970s with oil-fired boilers.  At some point it had failed, or the homeowner wanted something slightly more efficient. That’s when the separate hot water heater was added.

The next thing I noticed was the large diameter black iron piping looping around the basement. When this boiler was originally installed, circulators were either uncommon or rarely used. The hot water was circulated throughout the system by gravity. Eventually, kitchens or bathrooms were remodeled upstairs and radiators had to be moved. The red B&G pump you see behind the boiler was added to the system later in its life to help circulate through the smaller piping used when relocating radiators.

We’ve talked about a couple of different ways this boiler system has been delivering water to the radiators, but where has that water been getting its energy? This boiler could have been coal fired in its original days, but I’m guessing in this case it was originally oil fired. In the boiler’s current state and last leg of its life there was a natural gas power burner added to the bottom of the boiler.

Replacement Boiler Design

By the time we finished tracing the piping and identifying the various modifications, the system had effectively told us its story. The challenge now was determining which elements of that seventy-year-old design still made sense and how to incorporate modern equipment without sacrificing the comfort the homeowners had enjoyed for generations.

I mentioned earlier that the contractor had already determined an end goal. The plan was to replace the existing boiler and tank type water with a single Lochinvar combi boiler. The combi boiler is perfect for this application. The homeowner will appreciate the additional floor space and, more importantly, the fuel cost savings going from a 60-70% efficient on/off boiler and 80% efficient hot water heater, to a 95 + % efficient condensing boiler.

I stopped in to check on the contractor mid-morning on day two of the install. They were wrapping up running the new flue piping down the existing chimney. The boiler was carefully placed on the wall ensuring they had proper pitch in the venting back toward the boiler (1/4” per ft at least).

Installers Dave, Sam and Jared were making quick work of this project. The existing cast iron boiler had already been broken down and taken off the job site. Kudos to them for lugging out the old six section behemoth without any fingers or toes being smashed. Jonle was able to keep the old domestic tank up and running throughout most of the process, leaving the homeowner without hot water for only a short time.

Now the install is complete and the homeowner is very pleased with the new look of the updated mechanical room. The homeowner should start to see savings right away now that their domestic water is coming from the 95% efficient gas fired boiler. The savings should be dramatic this winter by pairing the modern condensing boiler with the existing cast iron radiation, especially here in Cincinnati where we tend to have milder winters. The on/off boiler we just replaced was operating at its lowest efficiency in the mild days of winter that make up roughly 70% of the winter days here in Cincinnati.

One of the biggest advantages of pairing a condensing boiler with cast iron radiation is the ability to operate at lower water temperatures for much of the heating season. The large surface area of the radiators allows comfortable heat delivery even when the boiler is running in its most efficient condensing range.

Projects like this remind us that every boiler room tells a story. Understanding how a system evolved over decades often provides valuable insight into its replacement. By respecting the original design while applying modern technology, we can deliver dramatic efficiency improvements without sacrificing the comfort homeowners have enjoyed for generations.