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Zephyr Industries VENT


Zephyr Industries POWER VENT, 12/24/48 Volt battery bank powered vent fan

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The Power Vent was designed for use in remote home power systems. The concept arose from field experience of systems with enclosed battery boxes. Quite often the CEC/NEC required venting was found back drafting, thus cooling the battery bank and lowering its’ capacity as well as venting hydrogen gas into the structure.

The Power Vent alleviates this condition by keeping a gravity operated damper closed within the vent pipe except at times when the batteries are being charged and producing hydrogen gas. During these times the battery box is force vented with a low power, sparkless fan which overcomes the damper sending the gas outdoors. The “fan on” mode is determined by the battery voltage. When the batteries are “gassing” during charge periods the battery voltage will read above normal. A voltage sensitive switch is required in the system to make the on/off determination, this is NOT included with the vent fan. Some inverters and charge controllers have a programmable auxiliary relay which can control the POWER VENT. Other systems may require the addition of a voltage controlled switch.

The Power Vent is designed around typical home power systems with battery banks under 2,200 amp hours and charge rates under 150 dc amperes. Systems larger than this can produce more hydrogen gas than the expel rate of the Power Vent which operates in the 5 to 8 cubic foot per minute range. Two vents may be used for higher volume.

Additionally hydrogen will set off a carbon monoxide detector. The PowerVent has been successfully used to prevent nuisance tripping of this sort when there is a crbon monoxide detector near the battery box.

Power Vents have also been used for other applications where low power ventilation is required. These include methane gas extraction from landfills, sewage sump tanks, outhouses, modest crawl space ventilation, beer tap line cooling and more.


  • Available for 12, 24, and 48 Volt
  • Positive venting of hydrogen gas
  • Stops back drafting
  • Puts the smell outside
  • Keeps batteries warmer in cold climates
  • Keeps the battery tops and terminals cleaner
  • Uses very little power
  • Excellent results for over 15 years!


Installation Instructions

The Power Vent must be placed vertically with the label right side up in order for the backdraft damper to function properly.

Place the Power Vent higher than the top of the battery box and indoors, especially in cold climates.

Use no more than four 90º bends including one at the exterior terminus facing down. Put a screen on the outside pipe terminus to keep insects and debris out. If installed in a dusty or construction environment put a porous foam or paper filter on the battery box inlet. DO NOT glue the Power Vents in place. Friction fit is adequate. DO NOT drip glue onto the fan blades. Use 2″ PVC DWV pipe on 12 and 24 volt systems. Use 2″ intake and 3″ output PVC DWV pipe on 48 volt systems.

Place a 1 Amp fuse (included) at the start of the positive circuit wire. Thermostat wire and phone splice/tap connectors (ULG or UG)) work well to connect the Power Vent. Use a cable tie around the base of the Power Vent and wires to provide strain relief and create a neat wire job

A controller is usually used in the circuit to cycle the fan . OutBack inverters and charge controllers may have a 12 volt powered auxiliary relay available. Other inverters may or may not have a voltage controlled auxiliary relay. Please refer to the appropriate manual for hook up and programming instructions. If no relay is available, a Solar Converters Simple Switch (model VCS1AH) may be used. (also check this websites faq’s). The voltage set points for turning the fan on and off are above the full state of charge voltage of the battery but below the battery gassing voltage. In the case of grid tied systems where the batteries are kept at float voltage 24 hours/day it may be necessary to run the fan full time as the batteries are always gassing. An alternative is to remove the backdraft damper to allow passive venting and only switch fan on when batteries are above float voltage.

For the inquisitive, please note that the 48 volt Power Vents are built with two 24 volt fans wired in series.

Recommended Set Points for Flooded Lead Acid Batteries

Battery VoltageFan OnFan Off
12 Volt13.2 Volt13.0 Volt
24 Volt26.4 Volt26.1 Volt
48 Volt52.8 Volt52.2 Volt




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