Size by peak demand, not bedrooms
Tanks are rated by first-hour rating (FHR). Tankless units are rated by flow at a given temperature rise. Winter inlet water in Central Texas is colder than many people assume, so a tankless unit that delivers 8 GPM in summer may deliver far less in January.
Hard water
Scale builds inside tankless heat exchangers and reduces performance. Plan on annual descaling, and consider a scale-reduction system. Tanks suffer too (sediment, rumbling), but more slowly.
Gas line and venting
A whole-home gas tankless may need 150,000–199,000 BTU/h. Many existing gas lines and meters were sized for a 40,000 BTU tank. Venting must also be rerouted.
Heat pump water heaters
Very efficient electric option, best in garages with space and airflow. Slower recovery than gas, but low operating cost.
Typical costs (2026)
- Tank replacement: $1,800–$3,800
- Gas tankless conversion: $3,500–$7,500
- Heat pump water heater: $3,000–$5,500
Try the Water Heater Sizer or book a hot water consultation.