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 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. 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 carbon monoxide detector near the battery box.