I have had one of these https://www.ecosmartus.com/ for about 8-9 years now. It is the 18,000 BTU mdl. 1200 sq ft house , 2 baths. It replaced a 40 gal electric heater. We have lime deposits in our water. I installed 2 sediment filters the the inlet side of the hot water heater and a filter on the outlet side to catch the lime scale deposits. I change the filters every 12-18 months. if you want to be able to use hot water at multiple locations at the same time. I would get the bigger unit 24,000 I think. But this works well for just the wife and myself. As stated it is nice to have unlimited hot water. The is no doubt in my mind that it paid for itself in 3-4 years. My electric bill went down considerably.