I just moved into the house about 3 months ago and for my first month living here I bought a tankless water heater and replaced my regular gas heater because the tankless takes up less space. I have it mounted on the outside. I paid a plumber to install it. It is a rheem water heater. For the past 3 months my bills have ranged from 300-400 in just gas alone. I had the gas company come out and I dont have a leak and the meter isnt running constantly. It only runs when I use the gas in the house. I dont have a kitchen yet installed so I don't use a stove. I havent turned on my ac/heat for the past 2 months so the only hting that could be using the gas is when I take a shower which is a 5 min shower daily. It's just me in the house. So why is my bill so high?? I am so concerned b/c I paid for the water heater got it installed and now it is costing me a lot of money. I checked to see what the previous owner used to pay in gas bills and it was way less than what I am paying and she used the regular hot water tank (not tankless). I threw out the old tank which uses a lot less BTU's than the tankless. I think the tankless uses 180k BTU's and I had a 40 gallon tank. I don't know what to do. And my plumber also checked for gas leaks and I don't have any.

I'm building a new house and was thinking about putting a tankless propane water heater in the house. My question is, I'm wondering if I can use a 100lb tank to fuel the heater and how long would it last under normal use? Like for a 117,00 btu heater.

I am looking into pruchasing a tankless water heater but do not want to pay more to operate it than the tank i have now. I know my tank runs on 1000 btu's and most tankless heaters run at about 10 thousand. Is it worth it to switch over?