Hoosier Efficiency from a Mod-Con Boiler

Hoosier Efficiency from a Mod-Con Boiler

Southeastern Indiana is not far from my office in Cincinnati, OH, where we affectionately call that state's residents Hoosiers. I think everybody has a nickname for their neighbors who live across the state line.

A contractor from that corner of the Midwest asked me to meet him at a job in one of the old Ohio River towns that dot the south shore of Indiana. We had collaborated on a custom residential job the previous year and he thought that maybe these fancy new boilers could be the answer for this job too. That unique job required radiant floor heat in a room that had three sides of wall to ceiling glass, a vaulted roof, and a stream running underneath. I was hoping that this job might be a little more straightforward.

A modulating condensing (mod-con) boiler provided a variety of supply water temperatures for floor heat in that great room/kitchen, kick-space heaters in an enclosed porch, a unit heater in the garage, and the domestic hot water. The homeowners loved the comfort while the contractor loved the flexibility. Now he wanted to apply the new technology to more than 100-year-old church and 52-year- old school, that were being heated with the original cast iron boiler put in when the school was built in '57. You have to love a boiler that has operated since Eisenhower was in office, but times change.

Site Visit Finds an 'Old' Problem
The chairman of the church's grounds and maintenance committee told us that he wanted the highest efficiency system. He had access to funds for a boiler replacement project if the new boiler(s) would save the congregation money. Knowing that saving energy and money is what mod-con boilers do best, I suggested we head for the boiler room, so that I could assess the situation.

As we made our way through the school to the basement, the conversation between the contractor and chairman was friendly. They seemed to know each other and shared many mutual acquaintances. I love the easy feel of smaller towns. Maybe these Hoosiers are on to something.

The boiler was positioned in the middle of the room, a survivor of what I could see were many years and at least a few flooded basements. The high water mark was painted on an adjacent wall, and was listed on the boiler jacket. I noted the rating plate: 1,750,000 BTUH input with a 1,400,000 BTUH output. That works out to exactly 80% efficiency. Check a few tags for yourself. The boilers from that era almost always have exactly 80% efficiency. Government regulation back then wasn't like it is today.

Most boilers are oversized. To confirm that, I performed a heat loss and radiation survey of both the church and school. I would calculate back at the office and work up a quote. In the meantime we wandered back to the boiler room. I explained the concept of mod-con efficiency to the chairman, specifically the following key points:

  • Mod-con boilers are most efficient when they can vary their supply water temperature with the outdoor temperature. This job allowed that.
  • Lower return water temperatures in mild weather drive efficiency up. Multiple mod-con boilers are more efficient than one mod-con boiler when they are staged in parallel modulation. This job also allowed that. Now that I had his attention, I went further.

Keeping Heat in the Building
Numbers are good, but visual evidence is better. I pointed to the 16-in. steel flue pipe running from the boiler to the chimney and asked, "How hot does that get?" He chuckled, and said he wasn't sure, but that he wouldn't put his hand on it. I explained that one way the mod-con boiler gets its efficiency is from flue gas condensation. Their plastic vent pipe is cool to the touch because the boiler takes the heat that was going up the chimney and applies it to the water heating the building. He was now seeing dollars that were exiting the building staying in the church coffers.

Another way the mod-con boiler gets its efficiency is from modulating the gas input. I told him that his existing boiler was burning 1,750,000 BTUH on a mild day or a cold day. It didn't know any better, and couldn't change that input if it wanted to.

Then, I told him that on a mild day, the new system could operate as low as 112,000 BTUH, less than 10% of the old boiler. The coldest day maximum input wouldn’t go above 1,197,000 BTUH if it was the three boiler system I had in mind, or about 69% of the old boiler’s input. The new staging control would vary that input automatically as the weather changed.

He asked how much he would save. I told him that the savings will vary and are based on too many factors to have a hard and fast equation. However, I told him, most reported savings are between 25% to 35% for replacing a large 80% cast iron boiler with a 95% multiple boiler system. Every system is different, so every savings percentage is different. He was very interested in getting a quote.

The Follow-up
The load came in around 950,000 BTUH. I usually size new boilers so that the net rating meets or exceeds the building load. The existing boiler's net rating was 1,190,000 BTUH, so not too far off. Remember, the boiler still lights off 1,750,000 BTUH when it only needs 200,000 on a fall evening. The three mod-cons I had in mind have a combined net rating of 990,000 BTUH. Two mod-cons in parallel modulation at 31% fire or 248,000 BTUH combined, would satisfy the fall evening load. That makes it around 85% less input. Less heat goes up the chimney. The contractor, Larry Dillard, president, Dillard Heating & Cooling, explained all of this with his presentation to the committee.

Dillard got the job. His installer did a masterful job on the installation, and finished well before the heating season. I met the chairman again, when I was out for the start-up. He seemed pleased with the committee's decision to go ahead with the project.

Epilogue: Efficiency is Documented
A year later, I got an email from Larry Dillard. The chairman had called him with some good news. The gas bills were in, and were tabulated and compared to last year. He even had the results charted. The bottom line was a calculated 48% dollar savings from the previous heating season with the old boiler. Now that is Hoosier efficiency. The degree day data for the two seasons was eerily similar. If you calculate a simple payback based on that average cost per year and the installed cost, the system pays for itself in about six and a half years.

The chairman was happy with his decision, the contractor was excited to have such a good reference, and I was glad that the system out performed our expectations. I always like when that happens.

Patrick Linhardt is the hydronic heating division manager at Habegger Corp. – Carrier Division, in Cincinnati, OH. He often lends his sleuthing skills and technical expertise to local contractors in need. To order his book, “Linhardt’s Field Guide to Steam Heating,” visit steamupairoutwaterback.com or call 513/703-5347.

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