Optimizing your steam heat boiler

Steam heat boilers have been a part of the fabric of New York City for gener­a­tions as a proven tech­nology for heating large multi­family build­ings. But now, with Local Law 97 (LL97) setting strict limits on the carbon emis­sions that a building may produce — and tight­ening those stan­dards grad­u­ally over time — many building owners are giving their oil- and gas-powered boilers a closer look, to see what improve­ments can be made to reduce emis­sions and costs.

Some build­ings with older heating systems may decide to do away with them entirely, opting for elec­tricity-powered heat pumps instead. Still others are choosing a more hybrid system that combines heat pumps with existing boilers. 

But there are energy effi­ciency gains to be made — and carbon emis­sions to be saved — by simply improving the oper­a­tion of an existing boiler and distri­b­u­tion system. Small tweaks can be made to make a boiler work smarter, before (or instead of) engaging in a complete retrofit. Below we’ll look at some of the system upgrades that are avail­able, and how much they can improve the effi­ciency of a steam boiler.

Do I have to replace my boiler?

One impor­tant factor to consider is whether upgrading an existing steam heating system will be econom­ical in the long run, or if a full system replace­ment might be required to comply with LL97 require­ments. For example, build­ings with boilers powered by No. 4 fuel oil (of which there are about 1,000 throughout the city) are required to phase out this type of oil by July 2027. These build­ings may find elec­tri­fi­ca­tion of heating and hot water systems to be the most cost-effec­tive solu­tion over the long term. For build­ings that use boilers powered by No. 2 fuel oil or natural gas, the retro­fits and improve­ments that can increase effi­ciency can be a worth­while way to save money on fuel consump­tion and improve resi­dent comfort in the process.

How to make steam boiler heating systems more efficient

1. Regularly clean and tune up boiler tank

Steam boilers are designed to reuse as much water as possible within the system, sending steam to heat resi­den­tial units and then recol­lecting cooled water, also known as conden­sate, through the same distri­b­u­tion system to be heated again. However, some residual conden­sate is always lost to leaks in the return piping. This requires water to be occa­sion­ally added to the system as replacement. 

Yet all added water contains dissolved oxygen, which attacks the boiler metal, and minerals that can coat the boil­er’s internal heat transfer surfaces, which can block some of the heat energy transfer from burners to water and reduce effi­ciency over time. 

This is why regular boiler service is essen­tial. (A good rule of thumb is to do this at least once per year.) Cleaning the entire system includes flushing the boiler tank completely of water, clearing out sedi­ment, and also cleaning soot from the fire­side of the boiler. Once cleaning is complete, the boiler tank can be refilled to the level set by the auto­matic water feeder, typi­cally measured by an internal probe or float.

Boilers in most resi­den­tial build­ings in New York City — that is, any building housing six fami­lies or more — are required to be inspected annu­ally by licensed profes­sionals, who may offer cleaning services during their inspec­tion. It’s usually worth taking them up on their offer, since a clean boiler can improve effi­ciency by up to six percent.

2. Add pipe insulation

Adding insu­la­tion to the pipes used to distribute steam throughout the building is one of the most cost-effec­tive ways of reducing heat loss and improving boiler effi­ciency. Uninsulated pipes allow signif­i­cant amounts of heat to be lost to the surrounding air, typi­cally right within the base­ment of the building, before it’s trav­elled very far. This allows the steam to return to liquid water, or ​“condense,” before reaching any radi­a­tors, forcing the boiler to burn more fuel to send more steam into the distri­b­u­tion system — essen­tially, working harder to send suffi­cient steam throughout the system. 

Modern steam pipe insu­la­tion is typi­cally made from fiber­glass or foam sleeves that are wrapped around the pipes and sealed at the joints to prevent heat loss and mois­ture intru­sion. The insu­la­tion usually comes in pre-formed, rigid sections sized to fit common pipe diam­e­ters, with an outer vapor-barrier jacket made of foil or plastic to keep conden­sa­tion out.

To install, sections are cut to length, fitted snugly around the pipe, and secured with tape, wire, or plastic bands. Elbows and valves can be covered using flex­ible fiber­glass wrap or custom-molded covers to main­tain contin­uous insu­la­tion along the entire pipe. (While you’re at it, you should insu­late your domestic hot water pipes as well.)

3. Check on the steam traps 

Steam traps are essen­tially valves that auto­mat­i­cally prevent steam from making its way back to the boiler before it has condensed into water. They allow air and conden­sate to pass through, but close off when hit by steam.

There’s also a partic­ular type of steam trap designed espe­cially for radi­a­tors, called a ther­mo­static radi­ator trap. This works to keep steam inside the radi­ator until it gives up all its heat and condenses back into liquid. Steam traps are gener­ally absent from one-pipe steam systems, but are found on both steam mains and radi­a­tors in two-pipe steam systems.

Without routine main­te­nance, these traps can malfunc­tion, allowing steam to be unin­ten­tion­ally vented from the system. Vented steam needs to be replaced with addi­tional water, which removes heat energy from the system, so preventing steam trap malfunc­tions can go a long way in increasing system efficiency. 

Just like cleaning the boiler, main­te­nance of steam traps located on a boiler’s primary piping system usually needs to be done while the system is not in use — usually during the summer — and it should be performed by a licensed professional. 

4. Tune up the burner

Burners kick off the steam heat process. Having the correct flame strength is essen­tial for creating the initial amount of heat needed to convert water into steam at the required volume based on inputs like outdoor temper­a­ture and apart­ment temper­a­ture. Because of this, it’s impor­tant that burners have the appro­priate mix of air and fuel for combus­tion to main­tain a consis­tent temper­a­ture, instead of swinging from too hot when fuel is being fired, to too cold when the burner is off. 

To ensure the burner is working as it should, it should be regu­larly tuned up. This involves cleaning the various air- and fuel-handling parts, and then adjusting the air-to-fuel ratio for clean and effi­cient combustion. 

On a modu­lating burner that has more than one firing rate, the air-to-fuel ratio should be checked, and adjusted if neces­sary, at multiple firing rates. Since burners operate with high volumes of combustible fuel, they should always be serviced by a licensed professional.

5. Improve heat balance

Uneven heating in different units of a building is caused by a variety of factors, including the posi­tion of the sun during the day, the direc­tion of prevailing wind, vari­ability in the air sealing of a building, etc. 

But one culprit for uneven heating can be the air vents. In one-pipe systems, these vents allow air to escape the radi­ator as it fills with hot steam. But some­times, steam can be prevented from reaching some radi­a­tors because the air inside the pipes is not pushed out by the steam fast enough, or at all. This is usually the result of failed radi­ator vents and/​or inad­e­quate air venting at the ends of steam distri­b­u­tion mains and the tops of steam risers.

Replacing failed radi­ator vents and adding new vents to the ends of mains (primary pipes connecting to boiler) and the tops of risers (vertical pipes to cary steam) will help air escape the system more quickly, which can reduce heat imbal­ance, leading to effi­ciency improve­ments of between 5 and 10 percent. Replacing failed air vents attached to radi­a­tors can be easily handled by most building supers; instal­la­tion of main and riser vents may require the services of a plumber or other professional. 

6. Install thermostatic radiator valves 

Thermostatic Radiator Valves (TRVs) control the amount of steam supplied to indi­vidual radi­a­tors, allowing resi­dents to adjust the temper­a­ture of their space. This increases resi­dent comfort and reduces fuel consump­tion, because boilers are not always supplying the maximum amount of steam to all radi­a­tors within the system. 

Adding TRVs can involve replacing parts of the distri­b­u­tion system that connect to the radi­ator, and in most cases should be done by a profes­sional plumber. If installed improp­erly, these retro­fits can lead to steam and water leaks, and should be performed by licensed professionals.

7. Improve temperature controls with a building management system

At its most basic, a boiler func­tions in a binary on/​off way — either the system is on, and heating water to a specific high temper­a­ture (typi­cally 180°F or above), or it’s off. But this can be a very inef­fi­cient way to run.

A step up from this, which many boilers in multi­family resi­den­tial build­ings already use, is an outdoor reset control (ORC). This system modu­lates the boiler’s run cycle and water temper­a­ture in accor­dance with the outdoor temper­a­ture. So for example, when it’s very cold outside, say 20°F, the ORC tells the boiler to run at full capacity, heating water to a very high temper­a­ture. But if it’s a warmer 40°F outside, it may not heat the water as high, or run as long. Some controls will turn the boiler off completely once the outside air reaches a certain temperature. 

For many years, ORCs, plus the addi­tion of TRVs, were the best tools a building had to improve a boiler’s effi­ciency. But new digital tech­nology has emerged in recent years to offer even more precise controls. These include Building Management Systems (BMS), which use sensors to control boiler oper­a­tion based on indoor temper­a­ture, not just outdoor. 

Take for example the Real Time Energy Management system, a propri­etary BMS created by Duel Fuel and installed at the Sherman Terrace co-op in the Bronx. This system allows building manage­ment to set the desired temper­a­ture for the entire building, and uses wire­less sensors and a modem to commu­ni­cate temper­a­ture data between indi­vidual apart­ments and the boiler in the base­ment. It also records all this data and sends alerts when energy use is out of the ordi­nary. BMS systems can be pricey to install, so they repre­sent a signif­i­cant capital invest­ment for many build­ings. But they can also pay for them­selves in energy savings.

What should I do first to make my boiler run more efficiently?

Not sure where to start? Here’s a quick check­list to help iden­tify visible or audible warning signs that your building’s steam heating system could benefit from one of the upgrades described above:

Visual cues

• Rust around the boiler, pipes, or radi­a­tors may indi­cate leaks, worn insu­la­tion seals, or conden­sate trapped within insu­la­tion that merit profes­sional inspection.
• Pooling water or visible water vapor are clear signs of leaks that require imme­diate attention.
• Uninsulated pipes in the base­ment or mechan­ical room are a clear sign of wasted heat.
• Discolored water during flushing can suggest sedi­ment buildup, meaning the boiler may need cleaning.

Physical cues

• Uneven heat between apart­ments or radi­a­tors often points to air venting issues.
• Overheated or under­heated rooms within the same unit may suggest the system would benefit from more temper­a­ture control from a ther­mo­static radi­ator valve..

Other potential Issues

• If the boiler runs constantly without main­taining steady indoor heat, that may indi­cate poor venting, water quality issues, or an outdated burner.
• If the annual inspec­tion sticker is missing or out of date, it may be time to schedule your law-required yearly inspec­tion by a licensed boiler technician.

Efficiency now, clean energy later?

Ultimately, each building will need to weigh the costs and bene­fits of retro­fitting an existing boiler against replacing it with a different, elec­tricity-powered system. No matter what they choose, investing in effi­ciency now will reduce fuel costs and ensure compli­ance with New York City’s tight­ening emis­sions rules. By plan­ning ahead, owners can turn what might feel like a regu­la­tory burden into smarter, cleaner, and more resilient building oper­a­tions — and a cleaner, more comfort­able city for gener­a­tions to come.

Reporting contributed by Camille Squires.