I asked this question a couple of months ago but I'd like to restate my problem and make sure I get it right. Installed unvented gas logs two years ago. The line for it originates between the gas furnace and gas water heater, about a 25 foot run with I think 5/8" copper, but maybe 1/2". I'm not at that house right now. Shut-off valve to the right of the fireplace. The OEM gas line running directly into the unit is small, so it seems 1/2 to 5/8 should be enough to feed it. But when the furnace kicks in, or the water heater, the fire gets sucked away and we have to relight the pilot also. It seems the easiest solution would be some sort of inline valve that prevents that backflow when another appliance kicks in, but I'm not aware of such a thing? Do I simply need still larger tube to the fireplace? Anybody experienced this? Thanks for any suggestions.