Where Is the Fan Noise Lowest on a Horizontal All-in-One Diesel Air Heater?

When a horizontal all-in-one diesel air heater runs overnight in a small cab, the perceived noise changes depending on where a person's head sits. The fan sound is not uniform around the unit. Knowing where it is quietest helps position the bed or seating for a better night's rest.

Noise Concentrations

The fan and motor sit at one end of the horizontal housing, close to the combustion chamber. Sound is strongest near that end and near the warm-air outlet, where air accelerates. The opposite end, away from the fan, carries the low hum of the cabinet rather than the direct fan noise.

How Distance and Ducting Help

Moving the outlet several centimetres away from where someone sleeps, and running a flexible duct, separates the listener from the direct sound path. The duct itself absorbs some tone before the air reaches the vent. A short, straight run is quieter than a tightly bent one that whistles.

Listening Before the Build

Testing the running unit in the chosen position, and placing a pillow where the head will rest, reveals whether the fan end points toward or away from the sleeper. Flipping the unit so the fan end faces the foot of the berth is often enough to make the night comfortable.

Using Duct Length to Soften Sound

A flexible duct between heater and outlet acts as a simple acoustic delay: the fan tone travels along the tube and loses some energy before it reaches the vent. A longer, gently bent run is quieter at the outlet than a short direct blast. Positioning the vent so it faces away from the sleeper's head further reduces what is heard.

Testing the finished install with the fan on its low setting, where overnight running happens, reveals the true rest-time noise. High-speed startup noise is brief; it is the low steady hum that determines comfort through the night.

References

GB/T 7714: YEK P N Y, LAU C E, LAU S Y, et al. A novel microwave air heater integrated with thermal energy storage [J]. International Journal of Energy Research, 2022, 46(13): 19269-19277.

APA 7th: Yek, P. N. Y., Lau, C. E., Lau, S. Y., et al. (2022). A novel microwave air heater integrated with thermal energy storage. International Journal of Energy Research, 46(13), 19269-19277.

MLA 9th: Yek, P. N. Y., et al. "A Novel Microwave Air Heater Integrated with Thermal Energy Storage." International Journal of Energy Research, vol. 46, no. 13, 2022, pp. 19269-19277.