Describe a normal day and a demanding one
When assessing domestic hot water, or DHW, explain when and how it is used. Two households with the same number of occupants may have different needs: one has several showers in succession each morning, while another spreads them throughout the day. Frequent guests or use of a bath should also be noted.
Prepare two scenarios: an ordinary day and a demanding but realistic one. There is no need to measure everything before the first conversation. Your account allows the professional to ask the right questions instead of selecting a capacity based solely on the number of occupants.
Distinguish capacity, service and recovery
The cylinder stores hot water to meet demand. Its volume matters, but does not by itself describe the entire service available. Water heating conditions, the incoming cold water and the system's ability to reheat after use also play a part.
Ask how the proposed solution responds to your scenario: several consecutive showers, two bathrooms used at the same time or occasional higher occupancy. A useful answer relates the equipment to those habits and makes the assumptions clear, without promising unlimited hot water.
Check the entire space, not just the floor area
Some solutions have integrated storage, while others use a separate cylinder. The choice must suit the home and the planned combination of equipment. Before setting aside a cupboard, check the specific model's dimensions and service clearances.
The visit should cover the route from the street to its final position, including turns, doorways, height and connection routes. A cylinder that fits on a floor plan may be difficult to bring in or inspect. Also explain whether the space is needed for other uses: using it for storage should not prevent access to the installation.
Ask how it works alongside heating and cooling
Where the system provides both hot water and space heating or cooling, its controls organise those services according to the configuration. Understand the intended operation and which controls will be available to you. The explanation should relate to your installation, rather than a generic demonstration of another product range.
Ask to be shown how to check the hot water status, which user schedules are available and how to report a loss of service. Protective settings and hygiene programmes must follow the manufacturer's and professional's instructions. Do not lower temperatures or disable functions to save energy without understanding their purpose.
Include taps and showers in the discussion
Your experience in the shower depends on more than the cylinder. Mention a long wait for hot water or a problem affecting only one tap during the assessment. Distribution pipework and fittings should be reviewed to distinguish what the proposed work is expected to improve.
Before accepting, ask for the cylinder, its position, the included services and the assumed usage conditions to be identified. Keep that information with the manual. If household habits change, it will help you review scheduling or consider an adaptation based on known facts, rather than starting again with an assumption.
More common questions
Is a larger cylinder always the best choice?
No. It should suit demand, available space and the way the system operates. Choosing by volume alone may overlook other important installation requirements.
Can an air source heat pump provide hot water only?
There are dedicated domestic hot water units as well as systems combining hot water with heating and cooling. The choice depends on the services you need and the existing installation.
Sources and technical reading
Some source documents are available in Spanish.