The systems store and deliver hot water differently
A storage heater keeps a tank of water hot and available. A tankless heater heats water as it flows through the unit. That difference changes sizing: storage equipment is discussed partly by tank capacity, while tankless equipment is sized around temperature rise and simultaneous flow demand.
Tankless does not mean unlimited flow. ENERGY STAR advises estimating the hot-water demand that may occur at the same time and having an installer verify the selected capacity.
- How many hot-water fixtures may run together
- Incoming-water conditions and desired outlet temperature
- Gas, electric, venting and condensate requirements
- Equipment location and service clearances
Conversion can be more than an equipment swap
Changing from storage gas equipment to tankless may require gas-line, electrical, venting, condensate, mounting, water-connection, permit, or utility work. Mesa’s published residential FAQ distinguishes like-for-like water-heater replacement from a traditional-gas-to-tankless conversion, but another jurisdiction may use a different rule.
Ask for a written scope that separates the unit, plumbing, venting, electrical, gas, permit, finish, and other-trade work.
- Same-type replacement or conversion
- Existing utility capacity
- Recirculation or long wait-time goals
- Maintenance access and isolation valves
- Local permit and inspection requirements
Maintenance and water conditions still matter
Storage and tankless systems both require manufacturer-consistent care. Hard-water scale can affect heated surfaces, but service intervals and procedures depend on the product, installation, use, and actual condition.
Choose the equipment after the demand and site assessment—not from a generic promise about endless hot water or automatic savings.
- Review the manufacturer’s maintenance requirements
- Confirm replacement parts and local service access
- Compare total installed scope, not only equipment price
- Plan before a failure when practical
Frequently asked questions
Does tankless hot water run forever?
A tankless heater can operate continuously within its capacity and utility limits, but simultaneous flow and temperature rise still determine performance.
Is tankless always more efficient?
Efficiency depends on the specific certified model, usage, installation, controls, maintenance, utilities, and distribution losses. Compare products and the complete installed system.
Can a tank heater be replaced with tankless in the same location?
Sometimes, but gas, electricity, venting, condensate, clearances, mounting, water piping, and permits must be checked before treating it as a direct swap.
Public sources
Related service pages
Need property-specific answers?
Call Dream Team Plumbing or book an appointment online. An on-site scope—not an article—determines the recommendation and price.