Water – How to go back to a gas water heater

Based on the International Residential code (which may or may not apply where you live), this installation is not compliant. Things that I see that need to be corrected include (but may not be limited to):

• The vent must be held at least one inch away from wood and other combustibles.
• The total rise of the vent must be at least five feet, to insure proper drafting.
• The vent must be sloped so that water/condensate will flow towards the appliance, by at least 1/4 inch per foot.
• Screws must be short enough that they do not pierce the inner metal of the vent.
• The length of the horizontal section (defined as sections at less than 45 degrees) must be less than 75% of the total rise.
• The vent cap outside must be a "type B" cap.
• Don't use tape because it would burn. Any small gaps should be OK since the exhaust will pull extra air into the vent, instead of letting the exhaust into the room.

Also, I see that one of the corrugated copper water tubes is a little flattened. You may want to replace it. Also, I see the plastic dielectric at the end of the tube on the right, but not on the left. If there is not any plastic dielectric, I'd suggest replacing it with a tube that has a dielectric. These connections do NOT need plumber's tape or dope. Also, these corrugated tubes should be replaced when the water heater is replaced.

The tankless water heater can be mounted with either concentric venting (preferred) or dual-pipe venting - one for intake and one for exhaust. Because of this, we would not be able to 'common vent' in with the furnace exhaust or even the chimney itself because the concentric would be pulling air down the chimney or suck in the exhaust of the furnace. We could take the exhaust pipe of the dual pipe option and add it to the chimney or furnace, if sized correctly, but regardless we'd still have to direct vent outside for the intake. So, because of this, it makes the most sense to go with the concentric venting and route it outside.

The best location that we're working with is in that old coal storage room. This provides access to 3/4" water lines and the 1" gas line that we can pull off of for the 3/4" line needed for the water heater. The only workaround now is with venting. The gas meter in my picture is actually farther down the exterior wall than is shown (the gas line does a 90 after coming through the wall) and up to where it's shown in the picture. This allows the easiest access to venting outside through this area, although we're required to keep a 3' distance from the gas meter for it's regulator. This shouldn't be a problem because we actually have to run it up the wall about 3' anyway to clear the snow level. If this isn't workable, the other option is to run the vent to the complete other side of the basement and come out of the wall there. This could come close to the maximum allowable vent span, but it's an option currently.