A new gas furnace is a fifteen to twenty year decision. Done well, you do not think about it again until your kids are out of the house. Done badly, you have callbacks every November, gas bills that surprise you, and a system that never feels right. The difference between a good furnace install and a bad one is rarely the brand on the cabinet. It is sizing, ductwork, commissioning, and the contractor doing the work.

This guide walks through how to actually pick a furnace for a Pittsburgh home. We will cover the four decisions that matter (size, efficiency tier, stages, brand), the two decisions that matter less than people think (cabinet color, fancy features), and the questions you should ask any contractor (including us) before signing a proposal.

Wahl has installed furnaces in Pittsburgh since 1980. We are a Rheem Pro Partner. We have seen what fails in this climate and what lasts.

Start here, before efficiency or brand: sizing

Sizing is the single biggest determinant of whether your furnace will work well or work badly. Bigger is not better. Bigger is worse. An oversized furnace short-cycles (turns on, hits setpoint too fast, shuts off, the house drifts down, fires again), and short-cycling is the cause of half the comfort complaints we hear.

Right sizing comes from a Manual J load calculation. This is the heat loss calculation HVAC contractors are supposed to do on every install. It accounts for:

• Square footage and ceiling height
• Insulation in walls, ceiling, and basement
• Window count, size, type, and exposure
• Air infiltration (how leaky is the envelope)
• Climate design temperature for Pittsburgh (we use 5 degrees as design, lower in some pockets)
• Duct losses if ducts run through unconditioned space

The output is a number in BTU per hour, typically somewhere between 40,000 and 100,000 for a Pittsburgh single-family home. The right furnace input rating is approximately that BTU number divided by the AFUE efficiency (so a 60,000 BTU load with an 80% AFUE furnace wants a 75,000 BTU input furnace).

If a contractor quotes you a furnace size based on square footage alone, without measuring or asking detailed questions about your house, find a different contractor. This applies to us too. Every Wahl quote includes a real load calculation, not a thumbnail.

Efficiency tier: 80% AFUE, 90%+ AFUE, or modulating

The three tiers map to three different value propositions.

80% AFUE standard. Eighty percent of the gas you burn becomes heat in your house, twenty percent leaves through the flue. Mature technology, lowest upfront cost, simplest to service. Vented through a metal flue and chimney in most installs. Best for rental properties, second homes, homeowners moving within five to seven years, and houses where high-efficiency does not pencil.

90% to 96% AFUE high-efficiency. Sealed combustion, PVC vent, condensate drain. Captures heat from combustion gases that 80% units waste. Real annual gas savings for long-term homeowners in Pittsburgh’s heating climate. Best for ten-year-plus owners, larger homes with high gas usage, and replacements for old 60% to 70% AFUE furnaces. See our high-efficiency furnace page.

Variable-speed modulating. Top tier, 95%+ AFUE plus modulating burner and variable-speed blower. Runs long cycles at low output, hits steady-state efficiency, mixes air better, runs quieter, integrates with zoning and IAQ. Best for two-story Pittsburgh homes with comfort issues, allergy or asthma concerns, and homeowners who want best-in-class comfort. See our variable-speed page.

How to decide: how long are you staying? Under five years, 80% AFUE usually wins on math. Five to ten years, the call gets closer and depends on gas usage. Over ten years, high-efficiency or variable-speed almost always pencils.

Single-stage, two-stage, or modulating

This is the burner control, separate from AFUE efficiency.

Single-stage fires at one output, 100%, every time. The thermostat calls, the furnace fires at full output, hits setpoint, shuts off. Simple, reliable, cheaper. Some short-cycling on mild days.

Two-stage fires at low (60 to 70% of rated output) most of the time, kicks to high only when low is not enough. Better comfort, less short-cycling, slightly more efficient.

Modulating fires at many output levels (40 to 100% in some units, with dozens of stages between). Best comfort, longest cycles, best efficiency. Pairs with variable-speed blower for a system that just runs.

Single-stage 80% AFUE is the value workhorse. Two-stage 96% AFUE is the popular middle ground. Modulating 97% AFUE with variable-speed blower is the top tier.

Brand: what matters, what does not

Brand matters less than installation quality, but it matters some. Three things to look for:

Dealer status with the manufacturer. Higher dealer tiers mean better factory training, deeper parts inventory, and longer warranty options. Wahl is a Rheem Pro Partner, the top tier. That status comes with extended warranties (twelve years on parts including the heat exchanger and labor on some configurations) that lower tiers cannot offer.

Local parts availability. Common failure parts (igniters, flame sensors, inducer motors, gas valves, control boards) need to be available locally on the truck or same-day from the supplier. Rheem, Trane, Carrier, Lennox, and Bryant all have good Pittsburgh parts availability. Some online and direct-to-consumer brands do not.

Warranty terms and clarity. Read the warranty. Standard manufacturer warranties run five to ten years on parts. Top-tier dealer warranties extend that. Labor warranties from the installer are separate. Wahl includes a one-year maintenance agreement on every install which covers the first annual tune-up.

What does not matter much: the specific brand color, the marketing language, the home show booth design, or whether the brand sponsors a NASCAR car. Furnaces are commodities at the equipment level. The installation and the warranty support are where the real differences live.

Ductwork is half the system

Most Pittsburgh homeowners replacing a furnace do not realize their ductwork is the limiting factor in comfort. The new furnace can be perfect and still feel inadequate if the ductwork is undersized, leaky, or poorly designed.

Common Pittsburgh ductwork issues:

• Undersized return air ducts (the most common problem, makes the blower struggle, reduces airflow, causes cold rooms upstairs)
• Disconnected or crushed flexible ductwork in attics or crawl spaces
• Supply runs that are too long or too restrictive for the furnace blower
• No return air on the second floor
• Leaks at every joint, sometimes 20 to 30% of conditioned air lost before it reaches the rooms

A good contractor will inspect your ductwork before quoting a furnace, identify any issues, and either correct them or tell you about them. If a new furnace is going into a duct system with serious problems, the furnace will not solve those problems.

Ask any contractor: “Will you measure the static pressure on my existing ductwork?” The answer should be yes. If they cannot or do not, that is a flag.

Cabinet orientation: upflow, downflow, horizontal

Most Pittsburgh basements take an upflow furnace, where the blower is in the bottom of the cabinet, air goes up through the heat exchanger, and out the top into the supply ductwork. Closets and utility rooms also typically take upflow.

Downflow furnaces have the blower on top, with air going down through the heat exchanger. Used in homes where the supply duct runs below the furnace (basement attic configuration, mobile homes).

Horizontal furnaces lay flat, with air going through horizontally. Common in attics and crawl spaces.

When you replace a furnace, you usually keep the same orientation. Some models are “multi-position” and can be installed in any orientation. Your contractor will know which fits your house.

Commissioning: the most overlooked part of any install

Commissioning is the verification that the furnace was installed correctly and is running to spec. It is not optional and it is not extra. It is the single biggest predictor of long-term reliability.

A proper commissioning includes:

• Combustion analyzer reading on the new furnace (gas valve pressure, CO output, flue temperature, combustion efficiency)
• Temperature rise across the heat exchanger (must fall inside the data plate range, typically 35 to 65 degrees)
• Static pressure measurement on supply and return ducts
• Gas pressure verification at the manifold under firing conditions
• Heat exchanger inspection
• Safety switch tests (limit, rollout, pressure)
• New filter and proper filter sizing
• Thermostat setup and walk-through

If you receive a one-page invoice with no commissioning data, you do not have proof that anyone verified the install. Wahl commissioning is documented in a checklist that goes in your file.

What you should not pay extra for

Some features are worth paying for. Some are not.

Worth paying for: – Variable-speed blower (real comfort benefit, lower electric usage) – Sealed combustion (high-efficiency models, eliminates draft issues and combustion air problems) – Two-stage or modulating burner (real comfort and efficiency benefit) – Manufacturer’s matched coil if you are also installing AC (warranty coverage and performance) – Surge protection on the outdoor condenser (low cost, real protection) – Smart or communicating thermostat with outdoor sensor

Not worth paying for: – Wi-Fi connectivity on the furnace itself (the thermostat is where Wi-Fi belongs) – Decorative trim packages – Brand-specific accessories that work no better than third-party equivalents – Extended warranties from third parties (the manufacturer’s extended warranty through a top-tier dealer is the right answer)

Questions to ask any contractor before you sign

Use these on every quote.

1. Will you run a Manual J load calculation on my house?
2. What is the static pressure on my existing ductwork and will the new furnace handle it?
3. What AFUE rating do you recommend for my house and why?
4. What stage of burner (single, two-stage, modulating) do you recommend?
5. What size in BTU input and why that size specifically?
6. What brand and what dealer tier do you hold with that brand?
7. What is the parts warranty? What is the labor warranty?
8. Will you address the chimney if I am moving from atmospheric to high-efficiency venting?
9. Does the proposal include a commissioning checklist?
10. What does annual maintenance cost and is it included for the first year?

We answer all ten in writing on every Wahl quote.

Common Pittsburgh furnace mistakes

Oversizing. The most common mistake, and a hard one to fix after the fact. If your existing furnace short-cycles, do not assume the new one needs to be the same size. Run a real load calculation. The new furnace is often smaller.

Ignoring the chimney. Moving from 80% AFUE to 95%+ AFUE means the new furnace vents through PVC, not the chimney. The water heater is suddenly venting into an oversized chimney that may not draft properly. Address this on every high-efficiency quote.

Cheap thermostat. A bargain-bin thermostat on a several-thousand-dollar furnace makes no sense. Spend on a good programmable or smart thermostat with proper heat pump or two-stage logic if applicable.

Skipping the load calc. Mentioned three times in this guide because it is the most consistent mistake.

Choosing on price alone. The lowest quote is sometimes the best deal. Sometimes it is the contractor cutting corners on commissioning, materials, or labor. Compare scope, not just price.

Schedule a furnace consultation

Call 1-855-GET-WAHL (1-855-438-9245) or schedule online. Free consultation, real load calculation, real options on paper.