There has been a lot of improvement in hot water heater (HWH) technology — units recover faster (heat water), use less energy, use outside air for combustion then power vent exhaust to the outside, all these changes result in healthier in-door air quality and lower energy bills.
What to look for when purchasing a Hot Water Heater:
1. Thermal efficiency: look for a 96% or better rating
2. Non-stop hot water for high demand, the ‘right sized’ unit is key
3. BTU input: More BTU’s the faster recovery
4. First hour delivery — how many gallons the unit delivers the first hour of use
5. GPH (Gallons per Hour) recovery: When in use, how many gallons the unit heats per hour
6. Venting: Outside air intake for combustion and power vent exhaust.
Can you install a high performance HWH in an existing home? Yes, here’s a link to a high performance unit by Slate Water Heaters shows some options:
http://www.statewaterheaters.com/lit/brochures/SRGBR00510.pdf