Demand is a simultaneous-use question
List fixtures likely to run together and the current hot-water complaint you want to solve. Gather utility and panel information only from safe, existing records or labels.
List the fixtures that may run at the same time and the hot-water result you expect at each. A large tub, several showers, laundry, and a dishwasher can create a different demand from one sink at a time. Incoming water conditions and the temperature rise required affect output, so a headline flow number alone is not a sizing decision. Ask the provider to show the assumptions used for your property and explain what happens when demand exceeds the selected unit's capability. Also discuss wait time at distant fixtures, minimum flow behavior, recirculation if considered, and whether the existing distribution piping affects the experience. Tankless equipment does not automatically remove the wait for hot water through a long pipe. Compare the expected household use with a suitable tank option before choosing a product.
List gas, electrical, vent, condensate, and space constraints
- peak shower and appliance use
- gas, electrical, vent, and condensate constraints
- water quality and manufacturer maintenance requirements
The conversion may be larger than the box on the wall
Compare total installed scope with a tank option, not just equipment price. Ask how performance assumptions will be documented and tested.
A tankless installation can require changes to gas or electrical capacity, vent or exhaust routing, combustion air where applicable, condensate handling, water connections, supports, controls, and service access. Ask which existing systems were measured or inspected and which need another qualified trade or utility. The proposed wall position should allow manufacturer clearances and maintenance without blocking exits or crowding other equipment. Water quality may affect service needs, so discuss the actual supply and manufacturer requirements rather than assuming every home needs the same treatment. Removal and disposal of the old tank, patching the former location, permit or registration, inspection, and startup should be included or expressly excluded. A product brochure cannot approve the installation, and a contractor should not promise compatibility before evaluating these conditions.
A sizing chart is not a field evaluation
Do not treat a product-size chart as an installation approval. Fuel, electrical, venting, and drainage work require the right qualified people and permits.
Maintenance belongs in the ownership comparison
Ask for the model's maintenance schedule, isolation and service provisions, water-quality conditions, warranty exclusions, and expected qualified service tasks. Keep access to the unit, valves, and drainage clear. Do not perform flushing or chemical cleaning from generic internet instructions because procedures and materials vary by model and condition. Compare the cost and inconvenience of required maintenance with the tank option being considered, without accepting unsupported savings promises. At startup, request a demonstration of normal controls and a test at the simultaneous demand discussed during design. Record delivered performance, error-free operation, leak checks, and any unfinished approval. If recirculation or another accessory is included, test that feature separately. The final documents should let a future service provider understand how the system was sized and what the installation depends on.
Ask how the selected model behaves during a power interruption and which functions depend on electricity even when another fuel supplies the heat. If backup power is proposed, it must be evaluated for the actual equipment by the appropriate qualified professional. Include that limitation in the household plan rather than assuming that changing from a tank guarantees hot water during an outage.
- What simultaneous flow and temperature rise were used?
- What utility upgrades are required?
- What maintenance and warranty conditions apply?