A combi (short for combination) boiler does two jobs in one unit. It heats the water for your home heating system (baseboards, radiators, or radiant floor) and it produces domestic hot water on demand for your showers, sinks, and laundry. No separate water heater required. Most combi boilers are wall-mounted, sealed combustion, high-efficiency condensing, and roughly the footprint of a kitchen cabinet.

For the right Pittsburgh home, that combination is the best of three worlds: less mechanical space used, lower combined gas usage, and one unit to maintain instead of two. Wahl installs combi boilers for homeowners who want to consolidate their heating and water heating, particularly in townhomes, smaller homes, and homes where the mechanical room is tight.

When a combi makes sense

The combi is a real upgrade in specific situations.

• Townhomes and rowhomes with limited mechanical space
• Smaller Pittsburgh homes where a tank water heater eats valuable basement footprint
• Homes where the existing boiler and water heater are both near end of life (replace both with one unit, one project, one set of efficiencies)
• Homes that want high-efficiency hydronic heat plus on-demand hot water
• Owners replacing an oil boiler and switching to gas

The combi is not always the right answer. Larger homes with two or more simultaneous hot water demands (two showers running at once, or a shower and a tub fill) sometimes exceed combi flow rate. Homes with significant existing radiator capacity also sometimes pencil better with a separate boiler and water heater. We will walk through the options.

How a combi boiler actually works

The boiler has two heat exchangers inside one cabinet.

The primary heat exchanger heats water for the space heating system. That water circulates through your baseboards, radiators, or radiant floor and returns to the boiler. The primary loop is sealed and pressurized, like any hydronic system.

When a hot water tap opens in the house, a flow sensor in the combi detects the demand. The boiler switches priority, sends the burner energy through a plate heat exchanger that transfers heat to the incoming cold water supply, and delivers hot water on demand. When the tap closes, the boiler returns to space heating priority.

The result is high efficiency (most combi boilers we install are 95% AFUE or better), instant hot water without a tank, and a single appliance to service.

What we install

• Wall-mounted condensing combi boilers (residential, 80,000 to 199,000 BTU range typical)
• Floor-standing combi boilers where wall mounting is not practical
• Outdoor reset controls (matches water temperature to the weather)
• New PEX or copper distribution piping where needed
• New near-boiler piping, expansion tank, air separator, dirt separator
• Sealed combustion vent and combustion air piping (typically PVC, side wall vented)
• Condensate drain or condensate pump
• New gas line sizing where required
• Smart thermostats and zoning controls

What goes into a Wahl combi boiler install

1. Heat loss calculation on the house to size the boiler for both heating load and domestic hot water flow rate
2. Existing distribution check, baseboard linear footage or radiator EDR (equivalent direct radiation)
3. Gas line sizing review (combi boilers often need a larger gas line than the old boiler used)
4. Vent and combustion air route planning
5. Condensate drain route
6. Removal of old boiler and water heater
7. New near-boiler piping, controls, and tie-in
8. Gas connection and pressure test
9. Vent and combustion air installation
10. Initial fill, purge, pressurization, and startup
11. Combustion analyzer reading on the new unit
12. Walk-through with the homeowner on the controls, condensate, hot water flow, and maintenance schedule

Pittsburgh-specific considerations

Three things come up often on combi installs in Pittsburgh:

Gas line size. A combi boiler under maximum demand (heating plus domestic hot water) often draws more gas than the old separate boiler and water heater drew. We check the existing gas line and upsize it if needed. We do this work in-house with our gas service crew, not through a subcontractor.

Hot water flow rate. A 199,000 BTU combi can typically deliver 4 to 5 gallons per minute of hot water at a 70-degree temperature rise, which is fine for one shower and a kitchen sink. Larger Pittsburgh homes with multiple simultaneous draws should consider either a larger combi or a separate boiler and tankless water heater.

Chimney. When you remove the old atmospheric boiler and water heater and install a combi (PVC vented), the chimney is no longer in use. We seal the chimney top and look at any other chimney-vented appliances during the quote.

Schedule a combi boiler quote

Call 1-855-GET-WAHL (1-855-438-9245) or schedule online. We walk the basement, run the load, and quote real options.