Skip to main content
Back to Glossary
Mechanical / HVAC

Boiler

In Plain English

A vessel that heats water or produces steam used to warm a building through radiators or heated pipes.

Definition

A closed vessel in which water is heated to produce hot water or steam for space heating, domestic hot water, or process applications. Boilers are fueled by natural gas, oil, electricity, or biomass and are rated by their output in BTUs per hour or boiler horsepower. Modern condensing boilers recover heat from flue gases to achieve efficiencies above 90 percent.

Why It Matters in Bidding

Boilers are often the single most expensive mechanical line item on a heating job, and their rating, fuel type, and efficiency drive not just equipment cost but venting, gas piping, electrical, and structural support that estimators must coordinate across trades. Choosing condensing versus conventional units changes both first cost and the value engineering an estimator can offer an owner weighing lifecycle savings.

Example

Bidding a school boiler replacement, the mechanical estimator prices two high-efficiency condensing boilers plus new flue, gas-train, and combustion-air work, then offers an alternate quote on a single larger unit to show the owner the cost trade-off.

Related Terms

Heat ExchangerBTUHVACHeat Pump

Frequently Asked Questions

A boiler line item rarely stands alone. Estimators must add flue and venting, gas or oil piping, combustion air, condensate handling on condensing units, electrical connections, structural pad or support, controls, and startup and commissioning. Rigging and removal of an existing unit on replacement jobs can also be significant, especially in tight mechanical rooms.
High-efficiency condensing boilers carry higher equipment and venting costs but lower operating costs, so they often appear as a value-engineering alternate. Estimators may present both a baseline and a high-efficiency option, letting the owner weigh first cost against lifecycle savings. Some jurisdictions or owner standards also mandate minimum efficiencies that constrain the equipment selection.
Boilers are rated by output in BTUs per hour or boiler horsepower, sized from the building's heating load calculation. Estimators price the specified capacity rather than resizing it themselves, since sizing is the engineer's responsibility. Confirming the scheduled capacity, fuel type, and quantity against the drawings prevents costly mismatches between the bid and the design intent.

Need more than definitions?

Get AI-powered bid alerts, automated form filling, and proposal drafting.

Start Free Trial

© 2026 ConstructionBids.ai — A LaderaLabs Product