HAUSE / WATER + HOME
Read tankless capacity at the temperature rise
A flow figure needs the test conditions beside it.
Keep the units explicit
Record incoming-water temperature and the proposed delivery temperature using the same unit. Their difference is a temperature rise, not a setting recommendation. Add the simultaneous fixture flows you want to discuss. The planning worksheet adds entered flows and subtracts entered temperatures; it does not certify equipment capacity.
Use the actual performance curve
Take those assumptions to the candidate manufacturer performance chart and the contractor. Ask which flow is available at the relevant temperature rise and whether the supply, venting and electrical requirements can be met. Do not compare two maximum flow numbers measured under different conditions.
Record uncertainty
If winter incoming-water temperature or fixture flow is unknown, leave a question for measurement. Ask about changes in simultaneous use and any commercial demands. A number created from estimates should stay attached to the estimates in the final quote discussion.