Easy answer: SAFETY
Let us explain. You’re in a bind, your water heater went out and you have family coming over. You have had the same water heater you had for 15 years and it’s worked fine, no one has been hurt.
What’s changed?
Laws, NYS Gas venting laws have changed. CO (Carbon Monoxide) is a silent killer and is the main reason why Federal, State, and local code laws have changed.
Why?
Well, let’s start with a question. When was the last time you had your chimney inspected? Chances are it has never been since the day it was built. Brick and mortar fall apart after many years and flue gas (non combusted fuel, CO, and vapor) can enter into the home. In the winter time it gets worse, flue gas (from a water heater alone) on a long unlined chimney can rise high enough to cause the vapor to freeze creating a blockage that will cause the vent to be plugged.
Alright I get it, what are my options?
Power vent water heaters. Power vent water heaters vent through the wall (TTW) usually through PVC. This solves all the issues with a standard vent water heater. Downsides? It’s almost twice as expensive.
Electric water heaters. Electric water heaters remove the need for venting.
Pros: It’s cheaper initially
Cons: The monthly energy cost is significantly higher. In places with higher kWh pricing, it will often cost you more over the life of the equipment vs a power vent natural gas water heater. Recovery is typically around 80 minutes.