Boiler Replacement in Chicago Two-Flats and Greystones

Chicago's housing stock is full of two-flats, three-flats, greystones and courtyard buildings heated by boilers. Many of those boilers are old, some very old. When one fails or becomes unreliable, owners face a decision that is more complex than replacing a furnace in a single-family home. The new boiler has to work with existing radiators and piping, often serves more than one household, and may have to vent through an aging masonry chimney.

This guide walks through the main choices, the factors that drive cost, Chicago-specific considerations for landlords, and the 2026 rebates available. When you are ready for a site visit, our boiler repair page explains how service works.

Signs It Is Time to Replace

• A leaking boiler. Water inside the cabinet or around the base, from a cracked section or corroded heat exchanger, is the most common reason for replacement.
• Frequent breakdowns during the heating season.
• Difficulty getting parts for very old controls or burners.
• Uneven heat across units or floors that maintenance has not fixed.
• Rising gas bills compared with similar winters.
• Combustion or venting problems, such as soot, spillage or carbon monoxide concerns.

Age alone is not always a reason. Some cast iron boilers run reliably for decades. But if the boiler is leaking or failing repeatedly, replacement is usually the better investment.

Decision 1: Steam or Hot Water?

If the building has steam heat today, the first question is whether to stay with steam.

Staying With Steam

Replacing a steam boiler with a new steam boiler keeps the existing radiators and piping, which is usually the simplest and least disruptive choice. Modern steam boilers are designed for better efficiency than the oversized boilers of the past. The keys to a successful steam replacement are:

• Sizing by connected radiation. Steam boilers should be sized based on the total radiator capacity in the building, not the old boiler's rating or the square footage.
• Correct near-boiler piping according to the manufacturer's instructions, which affects how dry the steam is and how quietly the system runs.
• Good venting of mains and radiators so steam distributes evenly.
• Low pressure settings.

Many steam complaints, such as banging pipes, uneven heat and spitting vents, come from piping and venting rather than the boiler itself. A replacement is a good time to fix them. Our guides on banging steam pipes and radiators not heating explain common problems.

Converting to Hot Water

Converting from steam to hot water can improve control, enable zoning and allow higher-efficiency condensing boilers. But it is a major project. Existing radiators and piping must be checked to confirm they can hold water under pressure without leaking, and some piping is usually replaced. Some old steam radiators are not suitable for hot water. Conversions make most sense when a building is being substantially renovated anyway.

Decision 2: Standard or Condensing?

Hot water boilers come in two broad types:

• Standard, non-condensing boilers typically vent through a chimney or metal flue and are generally less expensive.
• Condensing boilers extract additional heat from exhaust gases, producing condensate and venting through plastic or stainless pipe. They can reach high AFUE ratings.

The catch is that condensing boilers only reach their rated efficiency when the water returning to them is cool enough for condensation to occur. Peoples Gas program guidance makes the same point: if return water is not cool enough, a non-condensing boiler may be the better choice. Many older radiator systems can run cooler water much of the winter with an outdoor reset control, which lowers water temperature on milder days. A designer should evaluate your radiators, heat loss and piping before you pay extra for condensing equipment.

Decision 3: One Shared Boiler or Separate Systems?

Many two-flats and three-flats have one boiler serving all units, with the owner paying for heat. Options include:

• Replace the shared boiler with a similar central system. Simplest and usually least expensive.
• Add zoning so each unit has its own thermostat while sharing one boiler. Easier with hot water than with steam.
• Install separate boilers or systems for each unit so tenants control their own heat and pay their own gas bills. This requires separate gas service, venting and piping and is a larger project, but some owners find it worthwhile.

Decision 4: Combination Boiler or Separate Water Heater?

A combination boiler provides both space heating and domestic hot water. Peoples Gas offers higher rebates for qualifying combination units that replace both an existing gas boiler and a gas storage water heater. Combination units save space and can be efficient, but hot water capacity has to match the household's needs, and in multi-unit buildings they are most practical when each unit has its own system.

Venting and Chimney Considerations

Many Chicago boilers vent into old masonry chimneys shared with water heaters. Replacing the boiler can change how the chimney performs:

• A new condensing boiler vents separately, which can leave a water heater alone in an oversized chimney. That often requires a chimney liner.
• A new non-condensing boiler may still need a liner if the existing chimney is deteriorated or unlined.
• Vent routing through exterior walls must meet code for clearances from windows, doors and property lines, which can be tight in Chicago's narrow lots.

Venting should be discussed clearly in every quote. It is one of the biggest variables in cost and one of the most important for safety. See our carbon monoxide safety guide for why proper venting matters.

2026 Peoples Gas Boiler Rebates

For Peoples Gas and North Shore Gas customers, the 2026 residential program lists:

• $150 for a qualifying steam boiler at 82.5% AFUE or higher.
• $300 for a hot water boiler at 90% AFUE or higher.
• $350 for a hot water boiler at 95% AFUE or higher.
• $400 for a qualifying boiler plus integrated domestic hot water unit at 90% AFUE or higher, and $500 at 95% or higher, when it replaces both an existing gas boiler and gas storage water heater.

Conditions include an active outdoor reset control on hot water boilers unless supply temperatures never need to exceed 140 degrees, new equipment in an existing building, an AHRI certificate, and an application within 30 days of installation or by December 31, 2026. Rebates are first come, first served and can change, so confirm current terms before purchasing. Larger multi-family buildings may qualify for separate programs, so ask your contractor.

Timing a Boiler Replacement

Boiler replacement in a multi-unit building usually takes longer than a furnace swap, especially with chimney, piping or venting work. Replacing in late spring, summer or early fall avoids leaving tenants without heat. Chicago's heat ordinance requires landlords to provide minimum indoor temperatures from September 15 through June 1, including 68 degrees during the day and 66 degrees overnight in most residential buildings with central heat. A failure in January creates urgent pressure, so planning ahead is valuable.

What Drives Boiler Replacement Cost

• Boiler type, size and efficiency.
• Steam or hot water, and whether any conversion is involved.
• Near-boiler piping work.
• Venting and chimney liner work.
• Controls such as outdoor reset, zoning and thermostats.
• Removal of the old boiler, which can be heavy and difficult in tight basements, and asbestos abatement if old insulation is present.
• Permits and inspections.
• Water heater changes.

Old boilers and pipes in Chicago buildings are sometimes wrapped in insulation that may contain asbestos. Do not disturb suspect insulation. If testing confirms asbestos, licensed abatement may be required before work proceeds.

Questions to Ask Contractors

• How will you size the new boiler? For steam, will you measure connected radiation?
• Will the near-boiler piping follow the manufacturer's instructions?
• For a condensing boiler, will our return water temperatures allow condensing?
• What venting and chimney work is included?
• Is an outdoor reset control included?
• How long will the building be without heat?
• Which rebates apply, and will you help with the paperwork?
• What warranties come with the boiler and the installation?

Living With an Old Boiler While You Plan

If your boiler is aging but not failing, you can take steps to keep it running while you plan and budget for replacement:

• Schedule annual service before the heating season.
• For steam systems, keep the water level correct and follow the manufacturer's guidance on low water cutoff testing.
• For hot water systems, keep pressure steady and fix leaks promptly.
• Keep the boiler room clear and well ventilated.
• Make sure carbon monoxide alarms are installed and working in every unit.
• Know where the boiler's emergency shutoff switch and gas valve are.

Collect two or three replacement quotes during the off-season so you are ready to act quickly if the boiler fails.

Communicating With Tenants During Replacement

If you own a rental building, tell tenants well in advance when boiler work is scheduled, how long heat may be off and how hot water will be affected. Provide contact information for questions. If work must happen during the heating season, plan for temporary heat and keep the outage as short as possible to stay within the heat ordinance requirements.

Combining Boiler Work With Other Upgrades

A boiler replacement is a natural time to address related items: replacing failed radiator vents and main vents on steam systems, adding thermostatic radiator valves for room-by-room control, insulating exposed basement heating pipes, upgrading thermostats, and replacing an aging water heater that shares the chimney. Bundling this work can reduce total labor and disruption compared with doing it piece by piece over several years.

It is also a good time to look at the building envelope. Air sealing and attic insulation reduce heat loss, which can allow a smaller boiler and lower gas bills for years to come. If you plan envelope improvements soon, tell your contractor so the boiler is sized for the building as it will be.

Permits and Inspections

Boiler replacement in Chicago generally involves permits and code requirements for gas piping, venting and electrical work. A reputable contractor will handle permits and explain the inspection process. Be cautious of quotes that are significantly lower because they skip permits or code-required venting work. Problems can surface later during a sale, an insurance claim or an inspection, and venting shortcuts can create real safety hazards for occupants.

Get a Boiler Replacement Assessment

If your boiler is leaking, failing often or near the end of its life, call (312) 638-0812 for an on-site assessment. We serve multi-unit buildings and homes across neighborhoods such as Logan Square, Rogers Park and Lakeview. If you are not sure what type of system you have, start with our guide on steam vs. hot water boilers.