Furnace and air conditioning.

Why River Forest houses are different

Most of River Forest went up between 1900 and 1940. The brick Tudors and Prairie-style houses toward Keystone and Lathrop, the frame two-flats near Harlem, the big foursquares along Park and Franklin were built for gravity furnaces or radiators, not for the forced-air equipment that sits in most basements today.

That history shows up in three places on every estimate. The ductwork was threaded through closets and chases after the fact, and it is often undersized on the return side. The chimney was built for a coal furnace and a water heater sharing one flue. And the electrical service was upgraded once, usually in the 1970s, to a standard that no longer fits a variable-speed blower and a two-stage condenser.

Two contractors can look at the same basement on the 800 block of Keystone and reach honestly different conclusions about how much of that needs to change. That is the source of most of the three-thousand-dollar gaps homeowners cannot explain.

What you are actually buying

A split system is two machines sharing one duct network. In the basement, the furnace burns gas to make heat and holds the blower that moves air all year. On top of it sits the evaporator coil, which gets cold in summer. Outside is the condenser, the unit with the fan. Two copper tubes, the line set, connect coil to condenser.

Replacing "the furnace and the AC" means replacing four things: furnace, coil, condenser, and usually the line set. The ducts, in most cases, stay. Roughly half of what you pay is those four objects. The other half is a day or two of skilled labor that permanently modifies your house: sheet metal transitions, venting, a condensate drain, gas and electrical connections, the permit, and hauling a 1994 furnace up a stairwell with a turn in it.

So read the estimate as an answer to one question: what are you going to do to my house? The number at the bottom is a consequence of that answer.

Reading the estimate, row by row

Most estimates follow the same order. Customer and site. Equipment with model numbers. Accessories. A prose installation scope. Included work. Exclusions. Warranty. Price and terms. If your page has a price and equipment but no scope and no exclusions, you are holding an estimate for an object, not a project.

These are the rows to compare, and what belongs in each.

Price. Installed cash price, no financing, no rebates subtracted. A monthly payment is not a price.

Furnace and air conditioner. Capacity, efficiency, staging, blower type, and the full model number for each of the three pieces. Without the model numbers you cannot check anything else.

Permit and removal. The Village’s permit sheet lists like-kind furnace and air conditioner replacement as not needing a permit. New equipment, new central air, a fuel or venting change, a relocation or new piping does need one, and the contractor must be licensed and bonded with the Village either way. The Village’s express-permit page also lists furnaces and air conditioners, so confirm with Building & Zoning at (708) 714-3552 before work starts. The page should say whether a permit is included, with the fee included or stated, and that the old equipment is hauled away.

Parts and labor warranty. Two different promises from two different companies. Separate rows on purpose.

Electrical work. Included, or exactly what is being assumed. "As needed" is a price that has not been set.

Installation timing. A window the contractor will commit to, not "to be confirmed."

Equipment in plain terms

Capacity. BTU for heating, tons for cooling; one ton is 12,000 BTU. An 80,000 BTU furnace and a three-ton condenser are typical for a moderate River Forest house. Bigger is not better: oversized equipment short-cycles, which leaves rooms uneven and, on the cooling side, leaves the house cold and clammy because the AC only removes humidity while it runs.

Sizing. Capacity should come from a load calculation, called a Manual J. In practice many replacements are sized by reading the label on the old unit. That inherits any 1988 mistake and ignores your new windows, attic insulation and finished third floor. Ask: did this size come from a calculation or from the old equipment?

AFUE. Furnace efficiency. An 80% furnace vents hot exhaust up the chimney. A 96% furnace is a condensing furnace: it vents cool exhaust through PVC out a sidewall and produces acidic condensate that needs a drain. The efficiency choice is therefore also an installation choice, covered below.

SEER2. Cooling efficiency under the current federal test. SEER2 numbers read slightly lower than old SEER numbers for comparable equipment, so a "16 SEER" estimate and a "15.2 SEER2" estimate may be the same machine. Ask both contractors for SEER2.

Staging. Single-stage runs full blast or off. Two-stage has a low gear it uses most of the time. Variable adjusts continuously. Longer, gentler cycles are what fix a second floor that runs five degrees warm in August, which describes half the tall narrow houses near Lincoln school. Staging is also the largest single price spread in the equipment half of an estimate.

Blower. A standard PSC motor or a variable-speed ECM. The ECM is quieter, ramps up and down, and uses far less electricity on long low-speed cycles.

Matched pair. The condenser and coil are rated together. A new condenser on an old coil forfeits the rating and often the warranty. "Matched coil" on the page is not filler.

Thermostat. Two-stage and variable equipment need a thermostat that can talk to it. Some brands use communicating controls that lock you into that brand's thermostat. Fine, but know before the wall plate goes on.

What drives the price

When two estimates are three thousand dollars apart, ask which half of the number is different.

Tier and staging. Single-stage to variable is the widest spread. If one contractor quoted single-stage and the other variable, you are looking at two products, not a price difference.

Efficiency and what it drags along. Going from 80% to 96% means new venting through an exterior wall, a condensate line, sometimes a pump, and often a chimney liner for the water heater left behind.

Ductwork. The most common invisible difference. One contractor priced a new return plenum; the other wrote "existing ductwork to remain." Both pages say furnace and AC.

Electrical, venting, drainage. Where "as needed" hides. Panels here were often last upgraded in the 1970s.

Labor and access. A one-day swap in an open utility room and a two-day job in a low coal-room basement with a turn in the stairs are different amounts of work. Ask how many installers and how many days.

Overhead. A company with dispatch, a service department and a phone that gets answered at 9 p.m. in February costs more per hour than a two-truck shop. Sometimes that is worth paying for. That is a judgment, not a scam.

Accessories. Filter cabinet, humidifier, surge protector, UV lamp. Some are useful in a dry old house. Some are margin. Did you ask for it?

Ductwork, venting and the water heater

This section is the reason River Forest estimates deserve a second look more than most.

Ductwork. New equipment has airflow requirements. If the return duct cannot move what the new blower expects, the system underperforms no matter how good the equipment is. Undersized returns are extremely common in houses where the ducts were added in 1955 and modified in 1988. Ask whether the ductwork was evaluated or assumed.

Venting and the orphaned water heater. If your furnace shares a masonry chimney with a gas water heater and the new furnace vents out the sidewall, the water heater is now alone in a flue sized for two appliances. The exhaust cools too fast, condenses, and eats the mortar from the inside. The fix is a stainless or aluminum liner, or a different water heater. A thorough estimate raises this. A thin one leaves it for installation day. See the chimney and water heater guides for the other side of this problem.

Condensate. Gravity to a floor drain is cheap. A pump, a long run, or a route through finished space is not.

Electrical. A disconnect, a dedicated circuit, or panel capacity. If the panel is full, someone has to deal with it and it belongs on the page with a number.

Warranties

Two warranties from two parties. The parts warranty comes from the manufacturer and covers components. The labor warranty comes from the contractor and covers the technician's time. In year three, when the inducer motor fails, the motor is free and the visit usually is not.

Most manufacturers offer the full parts term only if the equipment is registered within sixty or ninety days. Unregistered, ten years often becomes five. Ask, in writing, who registers it and when you will see confirmation.

Labor terms of one and two years are common and are one of the most useful differences between otherwise identical estimates. Ask whether diagnostic time is covered. Ask what happens if the contractor is no longer in business.

Coverage lapses for reasons unrelated to the equipment: missed registration, mismatched coil, skipped annual maintenance where the terms require it, unpermitted installation. Keep a folder.

Heat pumps and dual fuel

A heat pump is an air conditioner that runs backwards in winter. Cold-climate models now work at temperatures that were unrealistic a decade ago, and a dual-fuel setup pairs one with a gas furnace that takes over when it gets cold enough. If a heat pump appears on your estimate, the questions are what happens on the coldest days, what the backup is, how the changeover is controlled, and whether your panel can take it. The heat pump guide covers this in full.

Timing and the HVAC calendar

A furnace estimate written during a January cold snap is priced in a different market than the same work in April. Contractors have a fixed number of crews, and most people replace a furnace the week it dies, which is the week everyone else's dies.

April to May and September to October are the shoulder seasons: crews have room, pricing is softer, and there is time for a site visit nobody rushes. If your system is still running and you are planning ahead, you are in the strongest position a homeowner can be in. Say so on the estimate and let contractors compete without a schedule squeeze.

Financing and rebates in 2026

Ask for the installed cash price first. Promotional financing often carries a dealer fee folded into the installed cost, so the cash buyer and the financed buyer are quoted different numbers for the same work. A home equity line or credit union loan is often cheaper over the life of the loan.

The federal Section 25C credit expired for equipment placed in service after December 31, 2025. If a 2026 estimate mentions a federal tax credit, ask which program. Nicor Gas pays a rebate on high-efficiency furnaces: $150 at 95% AFUE or better and $225 at 97% or better on its 2026 application, filed after installation. ComEd’s heat pump rebates have been substantially larger than Nicor’s furnace rebate and are normally handled through the contractor or distributor; check ComEd for the current amount. Ask whether the price shown is before or after any rebate, and who files.

Red flags

• No model numbers.
• "As needed," "if required," or "not specified" beside electrical, venting or ductwork.
• A discount that expires tonight.
• A financing pitch before you have heard the cash price.
• A diagnosis of a cracked heat exchanger with nothing to show you.
• No installation window and no statement of how long the price holds.
• Silence on the line set, the water heater vent, or where the condensate goes.

Questions to ask

• What are the full model numbers of the furnace, condenser and indoor coil?
• Did the size come from a load calculation or from the old equipment?
• Single-stage, two-stage or variable, and why that for my house?
• Does this include duct modifications, and what if more are needed once you open it up?
• Is electrical work included, and does my panel have capacity?
• How is the new furnace vented, and does that change how my water heater vents?
• Is the line set replaced, flushed or reused?
• What is the labor warranty, in years, and does it cover diagnostics?
• Who registers the parts warranty, and when do I get confirmation?
• What is the installed cash price, and how long does it hold?
• How many installers, how many days, and if the job needs a permit, who pulls it?

Go deeper

Five longer articles cover each part of this guide in detail: how to read the estimate, what drives the price, equipment explained, warranties, and questions to ask.

The short list

Before you compare anything, find these on the page: three model numbers; capacity and efficiency for each; the installation scope paragraph, read twice; every "as needed" circled; both warranty terms in years; the cash price and how long it holds. Anything you could not find is your list of questions.

Then put a second offer next to it. It is an evening you would rather spend at a Bulldogs game, and it is worth it.

Permits, programs and the Village