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Duct Smoke Detector Facts and Wiring – Short #203

By Bryan Orr

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In this short podcast, Bryan answers a listener-submitted question about duct smoke detector facts and wiring. He focuses on Honeywell duct smoke detectors (namely the D4120W), but there are some general best practices that can be applied to most duct smoke detectors.

The power supply may be 24v or 120v AC or DC and may have multiple inputs. You should not break that constant power source. There are also fan shutdown contacts, which may be normally open (alarm condition) or normally closed (non-alarm condition). Supervisory contacts open to indicate a trouble condition to the panel when something in the circuit isn’t working properly (NOT an alarm condition). There is often a resistor at the end of the loop, and the alarm panel recognizes a specific resistance. Alarm initiation contacts close and create a shorted condition when there is an alarm condition (the supervisory contacts open if there is a trouble condition).

Smoke detectors in the ducts are different from the ones on ceilings; they usually shut down blowers to prevent the distribution of smoke through the ductwork (and possibly exhaust it to the outside). They are required in duct systems designed for more than (or at least) 2000 CFM per NFPA90 and IMC 606.2.1, though those codes conflict. NFPA90 requires installation in the supply duct, but IMC 606.2.1 requires installation in the return; the AHJ may interpret the code either way. (Smoke detectors in systems >15000 CFM must be in both the return and the supply.)

Overall, remember that different detectors are suitable for different velocities. You will want to keep them downstream of bends for at least 18 inches, test them according to the AHJ, and ensure that they are mounted in the right configuration as recommended by the manufacturer.

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Author:

Bryan Orr

Company: Kalos Services

Position: Co-Founder and President

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Heat pumps may be everywhere, but according to David Richardson, the industry is in danger of aiming at the wrong target. In this 2026 HVACR Training Symposium session, the Kentucky contractor’s son, who has never lived in a home without a heat pump, opens with the story of Olympic rifle shooter Matthew Emmons. Emmons hit the bullseye with perfect precision in 2004, only to discover he had fired at the wrong lane’s target. Richardson argues that contractors risk the same mistake when they treat the heat pump itself as the goal and market it with the same “magic” promises used in the 1970s, a pattern that led to poor installations and a reputation problem that has lasted 50 years.

The real target, Richardson says, is the customer, and the heat pump is only one ring on that target alongside ductwork, the building envelope, equipment sizing, noise, and expectations. He distinguishes between HVAC equipment, which anyone can sell, and the HVAC system, which is where a contractor’s skill and craftsmanship show up. Average installations, he notes, deliver roughly 57% of rated performance, while a high-performance retrofit aims for 88% or better. With “free heat pump” offers likely coming next, he urges contractors to differentiate through engagement, education, clear expectations, and measured results, ending with what he calls a “craftsmanship receipt.”

The heart of the talk is five practical tips. First, learn what the customer is really after and set expectations early, including what a defrost cycle looks like. Second, don’t inherit a bad duct system, and use pressure, airflow, and temperature measurements to find problems before they become yours. Third, don’t inherit a bad building, since the structure works like a duct system and can undermine a perfect install. Fourth, bring the customer along by putting simple tools in their hands, such as a thermal camera or flow hood, and translating data into plain language. Fifth, follow a repeatable process that defines where testing begins and where additional paid services start.

Richardson closes with a call to document lessons learned, including mistakes, and to build these practices into company culture. His message is that heat pumps aren’t magic, but they can perform as if they were when installed well and priced to reflect the work. The session wraps with audience questions.

Topics Covered

The Olympic shooter analogy: precision aimed at the wrong target
History of heat pumps, the 1970s energy crisis, and early marketing hype
Why heat pumps shouldn’t be treated as a silver bullet, and the “silver buckshot” approach
HVAC equipment versus the HVAC system
Installation performance benchmarks: roughly 57% for average work, about 6% more for code-approved work, and a goal of 88% or better
The three E’s: engagement, education, and expectations, plus measured results
The craftsmanship receipt and verification: “if you don’t test, you’re just guessing”
Setting customer expectations, including cold-climate performance and defrost
Right-sizing and the pitfalls of oversized equipment, even with inverter technology
Testing for pressure, airflow, and temperature (PAT) and not inheriting bad ductwork
Building science basics: leakage, room pressures, blower doors, and thermal imaging
Using Socratic questions and plain language to involve the customer
Avoiding data overload and using tools like Measure Quick and the TrueFlow Grid
Following a process and getting paid for diagnostics, basic versus advanced retrofits
Learning from mistakes and changing company culture

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, and Filtrete.

Resources

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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