A boiler replacement scope should settle the boiler type (condensing or non-condensing), the vent and combustion air path, the piping arrangement and pumps, water treatment and flushing, the permit and inspection steps, and the shutdown window. Condensing boilers change the return water temperatures, vent material and condensate disposal, so the choice reaches well beyond the boiler itself.
- Pick the boiler type before pricing: condensing efficiency depends on low return water temperature, which the existing heating loop may not provide.
- Venting and combustion air are separate from the boiler and often cost more than expected. Write them as their own line items.
- Piping arrangement, pumps and controls need a drawn design, not a nameplate swap.
- Flushing and water treatment protect the new heat exchanger; include them in the base scope.
- Shutdown windows matter most in heating season. Plan temporary heat or a staged swap if the building cannot go cold.
Condensing or non-condensing, and why it changes the scope
A boiler scope that says replace with equal hides a decision. A condensing boiler recovers extra heat by cooling flue gases until water vapor condenses, which only happens when return water is cool enough. A non-condensing boiler tolerates hot return water and a simple vent. Many older Southern California buildings were designed around high supply temperatures, and their radiators, coils or fin-tube may not suit lower temperatures without changes.
| Question | Condensing | Non-condensing |
|---|---|---|
| Return water | Needs low return temperatures to condense | Tolerates high return water |
| Vent | Plastic or special stainless, sealed, with condensate | Metal vent, often draft-dependent |
| Condensate | Needs a neutralizer and a drain | Little or none |
| Piping | Often primary/secondary with reset controls | Often simpler loops |
| Design question | Can the existing terminals work at lower temperature? | Does the existing vent and stack suit the new unit? |
State the assumed type in the scope, and require the bidder to explain any difference from the existing system. The equipment background is in the commercial water heaters and boilers guide, and day-to-day service is covered under boilers and hydronic heating.
Venting and combustion air
A boiler cannot fire without a safe path for exhaust and a supply of air. This is where old rooms cause surprises: a flue sized for the old unit, a masonry chimney that is lined for another fuel, or a mechanical room with no outside air opening.
- Vent material, size, route, termination location and clearances to openings, intakes and property lines.
- Whether the existing flue or chimney can be reused, relined or must be abandoned.
- Sealed combustion (direct vent) versus room air, and the combustion air louvers or ducts that go with it.
- Roof or wall penetrations and who flashes them.
- Gas piping size, regulator, and the load of any other appliances on the same line. Confirm utility service capacity with SoCalGas or the serving utility as needed.
Local air district rules and the California Mechanical Code affect gas-fired equipment; confirm current requirements before the bid and state the assumptions used.
Piping, pumps and controls
Primary/secondary piping uses a short common section so the boiler loop and the building loop can flow independently. It is common with condensing boilers, because it keeps flow through the boiler steady while the building demand varies. The scope should describe the arrangement and name what is new: boiler pumps, system pumps, closely spaced tees, air separator, expansion tank, backflow prevention, relief piping, isolation valves and strainers.
- Pump sizing assumptions and whether variable speed is included.
- Outdoor reset, boiler staging and lead-lag logic if there is more than one boiler.
- Connection to the building automation system for status, alarms and setpoints.
- Low-water cutoff, high limit and flame safeguards tested and documented.
Contractor shall remove the existing boiler, install a new boiler of the specified type, and provide primary and secondary piping, pumps, air separation, expansion control, relief valve discharge piping and isolation valves as shown on Contractor's submitted drawings. Contractor shall provide a written sequence of operation for boiler staging and outdoor reset and shall test all safety controls at startup.
Flushing, water treatment and the heat exchanger
Magnetite sludge, scale and old inhibitor will end up in the new heat exchanger if the loop is not cleaned. Include a flush or chemical clean of the existing piping, dirt and magnetic separation, and a fill with the right chemistry. Say who sets the target water quality, whether a treatment provider is involved, and whether makeup water is metered. In California, local rules may restrict discharge of treated water, so state how drained water is handled.
The same discipline applies to chilled water loops. See chiller replacement scope of work for the comparable steps.
Permits, inspections and who owns them
Boilers are regulated equipment. Depending on size and use, expect a mechanical permit, a gas permit, electrical permits for work done by licensed electrical contractors, and in some cases jurisdictional or insurer inspection requirements. Healthcare and school buildings add oversight, such as HCAI and DSA, discussed in hospital and clinic HVAC scope of work and school HVAC modernization scope of work.
- Confirm which permits apply and who pulls each.
- Submit equipment and vent data if required for plan review.
- Schedule inspections at rough-in and final, with allowance for re-inspection.
- Obtain signoff before releasing the boiler for continuous service.
Confirm current requirements with the building department. They vary by city and change over time.
Shutdown windows and keeping heat available
Southern California has a mild but real heating season, with the coldest mornings in winter and often a short window in late spring and early fall when no heat is needed. Swapping outside that window is the cheapest plan, and the one to try first. If the building needs heat, multiple boilers can be replaced one at a time, or temporary boilers can be brought in with a documented hookup. Spaces that use steam or hot water for process or domestic hot water need their own plan.
Long lead times affect timing too. Order in time for the window, not after it opens.
What is commonly missed
- Asbestos or other hazardous materials in old insulation and gaskets; abatement must be named to a qualified party.
- Condensate neutralizer and the drain route for a condensing boiler.
- Seismic anchoring and housekeeping pad.
- Gas shutoff, sediment trap and pressure test.
- Flue gas analysis and combustion tuning at startup.
- Insulation on the piping that was disturbed.
- Electrical feeders and disconnects, which need a named licensed party.
- Boiler room ventilation and door or wall openings for the new unit.
Submittals and closeout
Submittals should show boiler data, vent and intake route, piping drawings, pump curves and a controls sequence. Closeout should provide startup and combustion test results, safety control test records, permit signoff, warranty registration, water treatment records and operating instructions. The new boiler can be loaded into the DaVinci Portal, together with the combustion readings and photos, so the first maintenance visit starts from a known baseline. When the boiler is part of a larger package, how to write a commercial HVAC scope of work shows how to tie it all together.