A garage should be properly ventilated near the floor to prevent any problems of this nature. In addition to that fact the water heater and furnace should be installed a couple feet off the floor on platforms. Additionally the garage should be a couple feet lower than any attached living space to prevent any infiltration. Granted, we all know that this is not always the case.<br /><br />The simple fact that all gas tanks including cars, trucks, boats, lawn mowers, etc. etc. are vented to atmosphere requires that these codes be followed for any construction of a residential garage. <br /><br />That is what a garage is designed for.... storing cars, trucks, boats, lawn mowers, etc. etc.<br /><br />So you do not need to bother taping the vents closed at all if you make sure your garage does not have any problems such as a water heater sitting on the floor.I don't put anything with gas in it in the garage anymore. That's because I have a natural gas water heater and furnace in the garage. Both have pilot lights. Years ago, my son's gocart was in the garage and the gas line began to leak. Luckily, I found it before the fumes had reached the pilot light in sufficient concentration to ignite. If that had happened, it would have been one bad scene. Around here, many houses have basement garages with gas appliances in them.