A power exhauster changes a venting system from a passive path into a pressure-managed assembly. The review must identify the inlet side, the positive-pressure discharge side, and the listed construction that keeps combustion products inside the vent.
Plain-English Highlights
IMC 801.14 requires appliance connections to a chimney or vent equipped with a power exhauster to be made on the inlet side of the exhauster. Joints and piping on the positive-pressure side must be listed for positive-pressure applications as specified by the exhauster manufacturer's installation instructions. The core review question is simple: is the appliance connected upstream, and is everything downstream suitable for the pressure it will see?
Permit Proof Chain
Appliance and fuel identified -> exhauster selected -> flow direction shown -> appliance connection located on the inlet side -> positive-pressure boundary identified -> downstream piping and joints listed for positive-pressure service -> manufacturer's installation instructions submitted -> termination, supports, access, condensate, power, and required safety controls coordinated.
Where To Show It
M-001: powered-vent design basis, pressure-boundary note, and manufacturer-instruction requirement. M-101: appliance, exhauster, flow direction, and full vent route. M-501: positive-pressure joints, supports, penetrations, drainage where applicable, access, and termination details. M-601: appliance and exhauster schedules with model, duty, electrical data, and vent-system basis. A/LS sheets: shafts, rated assemblies, roof and wall penetrations, and termination coordination. E/controls sheets: power source and the manufacturer-required operating and safety sequence.
**Do** - Draw the flow arrow and label the inlet and discharge sides of the exhauster. - Connect the appliance on the inlet side. - Identify the positive-pressure portion of the vent system. - Specify listed positive-pressure piping and joints based on the exhauster instructions. - Coordinate access, supports, penetrations, termination, and required controls before permit issue.
**Do Not** - Connect an appliance on the discharge side of the exhauster. - Treat standard vent joints as acceptable for positive pressure without listing evidence. - Use a generic powered-vent note without the selected manufacturer's installation requirements. - Treat the exhauster as an electrical device only; it changes the vent-system pressure and leakage risk.
Masterbuild QA Lens
Draw the pressure boundary. A reviewer should be able to trace, in one pass, the appliance connection, exhauster inlet, exhauster discharge, listed positive-pressure assembly, and termination. If that path cannot be traced, the design is not permit-ready.
Drawing / Submittal Check
Require the exhauster product data and installation instructions, then compare them with the plans and schedules. Confirm flow direction, connection side, allowed vent materials and joints, support and access requirements, electrical characteristics, termination limitations, and the applicable operating and safety sequence. Field selection is not a substitute for a coordinated design basis.
Common Review Risk
The typical failure is a fan symbol inserted into an otherwise natural-draft detail. The drawing does not identify upstream versus downstream, standard vent materials continue through the positive-pressure side, and the exhauster instructions are missing. The result can be flue-gas leakage, carbon-monoxide exposure, corrosion, condensate damage, nuisance shutdowns, and failed inspection.
When To Escalate
Escalate multiple-appliance systems, natural-draft appliances proposed downstream of a mechanical flue exhauster, existing-chimney reuse, missing manufacturer data, unclear positive-pressure listing, unresolved condensate or corrosion conditions, and any design where loss of draft could affect safe appliance operation. Verify the related Section 804 mechanical-draft requirements and the applicable fuel-gas provisions where relevant.
Field Tip
Mark the exhauster on the plan, add a flow arrow, and draw the positive-pressure boundary. That one markup exposes the two most common problems immediately: a connection on the wrong side and downstream vent components without the required listing.