I purchased a water heater from my brother-in-laws plumbing supply company that he works for. I thought I needed a 40 gallon water heater but I find out that it is a 50 gallon water heater. They do not take things back even if I have not opened the box. I have a 2700 sqft 2 story home. It has 3 full bathrooms. There are four adult family members that live in this house of which only my wife and I take a shower in the morning. Do you think a 40 gallon gas water heater will be enough to replace the 20 year old 50 gallon gas water heater we have now?