8.1.3. Heater sizing<br>

### 8.1.3. Heater sizing

Sizing of convectors is performed according to the following principles:

- the heat output of convector should be as close to the required as possible; undersizing and oversizing of convector is acceptable,

- dimensions of the convector should fall within set limits (length, height and depth separately). These limits are also imposed by the lengths and heights of recesses under windows taken from the base drawing: plan view and data on building structure. An alternative is the “Smallest within range” method, where minimum and maximum dimension must be specified. You can combine the two methods, e.g. apply “Fit to recess” method for the height, and “Smallest within range” method for length and depth. In this case the smaller depth is preferred,

- to the required output allowances are added for enclosure, location (not under window) and non-standard manner and direction of supply. If an integrated convector or a convector with thermostat on circuit pipe is used, an allowance for faster heating of room after heating output drop is also taken into account.

The heater is selected from a catalogue and from selected folder with, for instance, a range of heaters of similar design and various sizes. Particular sizes may have various availability status assigned – available immediately or on request. In calculation options you decide individually for every catalogue used whether this status is to taken into account.

The heat output of each sized heater is converted into thermal parameters (supply and return temperature, room temperature) using formulas specified in the EN-442-2 standard. This ensures that calculations are accurate within a wide range of parameters of the medium, including temperature drop. Initial return temperature is assumed on the basis of data, as every heater has a specific Delta_t indicating expected temperature drop of the medium. After final sizing this value usually differs from the initially assumed. This is because the temperature drop is adjusted in such manner as to provide the required output from the heater (usually oversized, rarely undersized). The same adjustment is made for heaters of user-specified size. Adjustment limit is specified in calculation options.