Pittsburgh is one of the few American cities where the boiler conversation is more important than the furnace conversation. Walk through Beechview, Bloomfield, Squirrel Hill, the South Side, Mt. Lebanon, Lawrenceville, or any of the older neighborhoods, and basements are full of cast iron boilers from the 1960s, steam boilers from the 1940s, and the occasional modulating-condensing unit installed in the last decade. Each type fits a different house, a different distribution system, and a different homeowner.

This guide walks through the six boiler categories Wahl installs, how to decide which one fits your home, sizing, brand, and what to ask any contractor. We are one of the few Pittsburgh contractors that runs meaningful volume across all six types, which means we will be honest about which one is right for your situation rather than recommending whatever is in our truck.

The six boiler types

1. Combi (combination) boilers

One wall-mounted unit handles both home heating and domestic hot water on demand. Compact, high-efficiency (typically 95% AFUE), popular in townhomes and smaller homes. Best for homes where the boiler and water heater are both near end of life and where the simultaneous hot water demand is one or two fixtures at a time. See our combi boiler page.

2. Standard hot water (hydronic) boilers

The workhorse residential boiler. 80 to 86% AFUE, atmospheric or power-vented, heats water and circulates it through baseboards or radiators. Reliable, well-understood, common Pittsburgh choice for replacement. Best for one-for-one swaps where the chimney is good and budget rules out high-efficiency. See our hot water boiler page.

3. Steam boilers

Pittsburgh older-home staple. Heats water to steam, sends it through cast iron radiators, condenses back to the boiler. No circulator pump needed, gravity returns the condensate. Best for any existing steam system, where conversion to hot water would be a major piping project. See our steam boiler page.

4. Cast iron boilers

Traditional, durable, 30 to 40 year service life. Cast iron sections joined with push nipples. Heavier and bigger than steel boilers, but lasts longer. Available in both hot water and steam configurations. Best for long-term homeowners who value durability over highest efficiency. See our cast iron page.

5. High-efficiency condensing boilers

95%+ AFUE. Modulating burner, sealed combustion, PVC venting, condensate drain. Best for long-term homeowners with cast iron radiators or radiant floor (the distribution that benefits most from low water temperatures). See our high-efficiency page.

6. Commercial boilers

Sized for multi-unit residential, schools, churches, light commercial. Often modular condensing for redundancy. See our commercial page.

How to decide which type fits your home

Five questions guide the choice.

What does your existing distribution look like? Cast iron radiators (one pipe or two pipe): steam if single-pipe and the system is currently steam, hot water if currently hot water. Baseboards: hydronic, ideally with outdoor reset controls. Radiant floor: high-efficiency condensing is the natural pairing. Multiple types mixed: zoning helps, condensing with mixing valves handles the mix.

How long are you staying? Under five years: standard hydronic or cast iron, lower upfront cost. Five to ten years: depends on distribution. Cast iron radiators favor condensing, baseboards lean toward standard hydronic. Over ten years: high-efficiency condensing usually pencils best with outdoor reset.

Is your water heater also near end of life? Yes, and you want to consolidate: combi boiler. Yes, but you want them separate: hydronic boiler plus separate water heater (indirect water heater paired with boiler is highly efficient). No, water heater is new: pick the boiler independently.

What is the chimney situation? Chimney is in great shape: atmospheric or power-vented hydronic works. Chimney is in bad shape and needs work: condensing boiler vents through PVC, no chimney required. Chimney is shared with water heater: needs a plan, condensing means liner or water heater swap.

What does the basement look like? Plenty of space: any type works, cast iron is fine. Tight space: wall-mounted condensing or combi. Closet only: combi or wall-mounted condensing.

Sizing a boiler

Boiler sizing follows the same principle as furnace sizing. Right-sized is critical, oversized is bad, undersized is worse.

For hot water boilers, the right sizing comes from a heat loss calculation (Manual J style or detailed room-by-room analysis). Most Pittsburgh single-family homes need 60,000 to 120,000 BTU of boiler input.

For steam boilers, the right sizing comes from connected EDR (Equivalent Direct Radiation), which is the total radiator capacity measured in square feet. The boiler must match the EDR closely. Oversizing a steam boiler is particularly bad because it short-cycles, leaves water in the wrong places, and never reaches operating temperature properly.

Most Pittsburgh boilers we replace are oversized, often by 50% or more. The original installer used a rule of thumb (BTU per square foot) and added safety margin. The new boiler is often noticeably smaller than the old one, and runs better as a result.

AFUE and what it really means

AFUE is Annual Fuel Utilization Efficiency, the percentage of fuel energy that becomes heat in your home over the heating season.

Standard atmospheric cast iron: 82 to 84% AFUE. Power-vented hydronic: 84 to 86% AFUE. Modulating-condensing: 95 to 97% AFUE.

The AFUE difference is real but it is not the whole story. A 95% AFUE boiler running with no outdoor reset on high-temperature baseboards may deliver only 86 to 88% real-world efficiency because the return water never gets cool enough to actually condense. The same boiler with outdoor reset on cast iron radiators delivers closer to 95% real-world.

The right way to think about it: AFUE is the laboratory number. Real-world performance depends on how the boiler is matched to the distribution system and how the controls are configured.

Outdoor reset is the key efficiency feature

Outdoor reset is a controls feature that adjusts the boiler’s supply water temperature based on outdoor temperature. On a 45-degree day, the boiler runs 130-degree water through the system. On a 5-degree day, it runs 180-degree water. The water temperature tracks the heating load.

Why it matters for high-efficiency boilers: condensing only happens when return water comes back below about 130 degrees. On a fixed-180-degree-supply system with high-temperature baseboards, the return water never gets cold enough to condense. Outdoor reset lowers the supply temperature on mild days, which lowers the return temperature, which lets the boiler condense and capture the efficiency gain.

Why it matters for standard boilers: even a non-condensing boiler runs more efficiently at moderated water temperatures, and short-cycling drops dramatically.

We install outdoor reset on every condensing boiler and on most standard hydronic boilers. If a contractor quotes a condensing boiler without outdoor reset, ask why.

Modulating burner and turndown ratio

A modulating-condensing boiler has a burner that adjusts its firing rate based on demand. The turndown ratio is the spread between maximum and minimum firing rate.

5:1 turndown: boiler modulates from 20% to 100% of rated output. 10:1 turndown: 10% to 100%.

Higher turndown means the boiler can match smaller loads (a single zone on a mild day) without cycling on and off. The result is longer run cycles, higher real-world efficiency, and better comfort.

For Pittsburgh applications with multiple zones or radiant floor, a 5:1 or better turndown ratio is the right target. Single-zone smaller homes can get away with less turndown.

Chimney considerations

The chimney is one of the most overlooked parts of a boiler replacement in Pittsburgh.

If you are swapping an atmospheric boiler with another atmospheric boiler, the existing chimney is probably fine. We inspect to confirm.

If you are moving from atmospheric to power-vented or condensing, the boiler no longer uses the chimney. But your water heater might. A water heater venting alone into an oversized chimney often fails to draft properly, condenses moisture inside the chimney, and in worst cases backdrafts carbon monoxide into the home.

Two solutions:

• Reline the chimney with a properly sized aluminum or stainless liner sized for the water heater alone
• Replace the water heater with a tankless, power-vented, or heat-pump water heater that does not need the chimney

We address chimney work on every quote. If your contractor does not, ask why.

Near-boiler piping is the part most installs get wrong

The piping right at the boiler matters more than most homeowners realize. For steam boilers, the header, equalizer, and Hartford loop have to be piped exactly to manufacturer specs or the boiler will surge and water-hammer. For hot water boilers, the primary-secondary piping or buffer tank configuration matters for cast iron sections and for protecting condensing boilers from cold returns.

We pipe boilers exactly per manufacturer specs. That sometimes means cutting out existing piping the previous installer left in place. It is the right way to do the job and we do not skip it.

What you get with a Wahl install

Every boiler install includes:

• Heat loss calculation
• Existing distribution inspection
• Boiler sizing
• Near-boiler piping per manufacturer specs
• Gas line review and upsize if needed
• Chimney assessment and plan
• New circulators (ECM where appropriate)
• New zone valves and controls
• Expansion tank, air separator, dirt separator
• Outdoor reset (on most installs)
• Combustion analysis at startup
• Documented commissioning checklist
• Walk-through with the homeowner
• One-year maintenance agreement included

Questions to ask any contractor

1. Will you run a heat loss calculation, not a rule of thumb?
2. Which of the six boiler types do you recommend and why?
3. Will the new boiler include outdoor reset?
4. What is the turndown ratio (for modulating-condensing units)?
5. How will you address the chimney?
6. Will you replace the near-boiler piping per manufacturer specs?
7. Are circulators ECM (variable-speed) or PSC (single-speed)?
8. What zoning configuration do you recommend?
9. Will commissioning data be documented?
10. What is included in the first-year service?

Schedule a boiler consultation

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