I currently live in a 2 story home and it has an electric water heater which is extremely expensive, I would like to switch to a gas WH. The problem is the utility room is on the first floor with no access to the second floor to run a chimney exhaust, can I vent it directly out the wall using double wall gas pipe and run it up the side of the house terminating about 3 feet above the bottom of the roof on the second floor? Or is there something else I can do?
There are a few options to choose from and there are several variables that might prevent any one of those installations. The one you mentioned, natural draft water heater installation, would probably be the least expensive, you’d just need to carefully calculate vent pipe dimensions, termination point, above the roof, and secure the entire venting system to your building structure.
The two other options / installations could be the easiest ones to perform but slightly more expensive. Power vent water heater – you’d just run one PVC pipe through the wall, the only concern on the outside would be exhaust discharge pipe clearances to any openings. Of course this one requires electrical power for the vent motor so you need to compare energy usage between the natural draft and power vented water heater. Also, the motor may not be that quiet, more here – https://www.checkthishouse.com/2991/water-heater-pvc-vent-pipe-and-power-venting.html
Direct vent water heater – it’s a more efficient and more expensive version of the power vent type. Just like the power vent one, this one vents through the side wall but with a different type of a vent pipe.
You could also opt in for a tankless gas water heater but it requires larger gas supply line and it’s quite expensive (the heater and its venting system).
There’s one more important thing you need to keep in mind, the natural draft and power vent type water heaters (single pipe) require combustion air from within the house to ensure proper burning. More details here – https://www.checkthishouse.com/2531/combustion-air-for-fuel-burning-appliances.html
There are also specific location restrictions that apply to those (except for the direct vent type) water heaters – for example they cannot be installed in sleeping ares or bathrooms.
Let me know if you have more questions but your best bet would be to ask some local professionals for installation suggestions. Sometimes you have to see the location to come up with a solution that is best under the circumstances.