Retrofit Before Replacement: Why Boiler Upgrades Don’t Work for Many Large Buildings

Heat pumps are often hailed as the future of heating. (We agree!) The push for reducing carbon emissions in buildings has made heat pumps a top choice for heating in new construction and smaller renovation projects , offering efficient heating and cooling in one package.

But nearly 80% of large buildings in New York City use steam systems for heating. These systems are often inefficient, uncomfortable, and rely on fossil fuels. Converting large NYC buildings from fossil fuel heating to heat pumps can be challenging in terms of capital and operating costs, as well as technical, logistical and political feasibility.

As much as we’d love to electrify everything overnight, the reality is that steam will be here for a while. So, what can we do within the constraints of the existing infrastructure?

Why Boiler Upgrades Alone Don’t Work

The Boiler Replacement Myth

It’s a common belief that swapping out old boilers for new ones will solve heating problems and save energy. However, data from industry evaluations and SWA’s own studies show that boiler replacement alone results in little to no energy savings.

Regardless of age, steam boilers operate at a peak efficiency range of 80–85%. New steam boilers don’t offer substantially improved efficiency, and the high return temperatures in steam systems prevent the use of higher-efficiency condensing boilers.

The Real Problem: Distribution

Heating complaints and outages are rarely caused by the boiler itself. Instead, issues like broken steam traps, poor venting, and malfunctioning condensate equipment are the real culprits behind discomfort and inefficiency. In many cases, the distribution system needs urgent repair, while the boiler still has decades of useful life left.

Rethinking Boiler Lifespan

With proper maintenance and a healthy steam distribution system, steel boilers are remarkably durable and almost infinitely repairable.

The service life of a boiler should not be measured in years but in the amount of freshwater exposure. Fresh makeup water (which is fed into a boiler when steam condensate is not returned) is corrosive to steel and leads to degradation of the vessel structure. This in turn leads to leaks and the need for welding repairs. Over time, the shell thickness of the boiler deteriorates past a point of no return, after which the boiler is not safe to operate and should be replaced. And luckily a skilled professional can test for boiler shell thickness to determine the risk of failure before spending money on a costly replacement.

Retrofit Before Replacement

Optimizing Steam Distribution

Rather than rushing to replace boilers, the most impactful improvements often come from optimizing the steam distribution system. Proven strategies include:

• Installing radiator orifice plates: Eliminates the need for radiator steam traps and ensures balanced heating.
• Replacing steam traps: Especially in basements, to prevent heat imbalance and energy loss.
• Adding robust air venting: Makes it easier to clear air from steam mains, reducing boiler workload.
• Restoring indoor temperature sensor controls: Optimizes modulation and reduces overheating.
• Cleaning and tuning boilers and burners: Adjusting firing rates and treating boiler water can address issues like wet steam and improve overall performance.

Learn more about how to upgrade steam systems here: Comprehensive Heating Upgrades for Two-Pipe Steam Systems

Real-World Results

New York City’s largest landlord, faced a portfolio-wide challenge: outdated steam systems and a high volume of resident complaints. The initial plan was to allocate nearly $1 billion for boiler replacements. But holistic assessments performed by SWA revealed that most boilers had plenty of useful life left, while distribution systems were the real source of problems.

By shifting the strategy to “retrofit before replacement,” they were able to:

• Avoid unnecessary boiler replacements and save millions in capital funds
• Focus resources on impactful distribution upgrades
• Lay the groundwork for future electrification

This approach not only improved comfort and efficiency but also aligned with long-term decarbonization goals.

The Road to Electrification

Electrification is ultimately how we get to our long-term carbon goals, but the economics for high-performance, all-electric retrofits are challenging in the short term for many buildings.

For new construction and upgrades to smaller structures, upgrading to heat pumps aligns with cost, carbon, and energy reduction goals. But the reality is that full electrification of large existing buildings isn’t always feasible in the short term.

The good news is that we have solutions to balance steam heating systems and operate them much more efficiently. These retrofits save energy and carbon, greatly increase resident comfort, and are still compatible with a long-term roadmap for full electrification.

Our consulting work with major NYC landlords helped refine steam policies to focus capital work on addressing the root causes of heating problems rather than traditional in-kind replacement of boiler plants. This approach optimizes capital funds, while still increasing efficiency and reducing carbon across the portfolio.

Final Thoughts

Steam systems aren’t disappearing overnight. For many buildings, the smartest, most cost-effective path is to optimize existing steam distribution systems now and save energy and capital for deeper carbon reductions in the future.

Contributors: William Kalbacker, Senior Mechanical Engineer; Kelly Westby, Managing Director, Building Operations, Decarbonization, and Efficiency at Steven Winter Associates