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→Heating
The spreadsheet uses the following formula to determine heating requirements in British Thermal Units per hour (BTU/h) [1]:
<pre>BTU = V * T * K * B</pre>
where:
<pre>V = volume of the accommodation in cubic metres
T = temperature differential in degrees Celsius
K = dispersion coefficient (how heat ‘lossy’ is your boat)
B = 4 (conversion factor to BTU)</pre>
To calculate the Volume, for each living space multiply Length * Width * Height in feet as shown in the below table. Use judgement in deciding whether to list each space individually or as part of a section. The calculator will do the conversion to metric.
For T, if you need to convert degrees F to degrees C, the formula is:
<pre>C = (F – 32) * 5/9</pre>
The dispersion coefficient K is adapted from housing construction as follows:
<pre>K = 3.0 - 4.0 (Simple construction, simple windows - Not insulated)
K = 2.0 - 2.9 (Simple construction, simple windows - Poorly insulated)
K = 1.0 - 1.9 (Standard construction, double-pane windows - Moderately insulated)
K = 0.6 - 0.9 (Advanced construction, triple pane windows - Well insulated)</pre>
With K=3, the calculator yields 19 BTU/ft-sq while experts recommend 20 BTU/ft-sq, so we have good agreement at one end of the range. How aggressive you should get towards the other end is impossible to say. However, with the three heating systems specified for the boat there should be ample scope for increasing or decreasing the heat without upsetting the balance of the system. In a system that is under-sized, the furnace will run for long periods. In an over-sized system, the furnace will cycle frequently and run for very short periods. In general, a heating system should be sized 154% of the requirement, so it runs at about 65% duty cycle.