I have been having some interesting correspondence with Peter Berry of nb Kelly-Louise regarding narrow boat central heating systems. Peter blogged about it <here>.
Our discussion led to us considering the probable need to ensure the diesel heater output matched the capacity of the radiators. If the output of heater is greater than the capacity of the system to dissipate the heat then hot water will be returned to the heater which may cause it to shut down. Alternatively, if the heater output is less than the capacity of the radiators then the heater might continuously run making the boat too hot. The former might lead to the “coking up” of the burner through frequent cycling whereas the latter is inefficient burning too much diesel.
Peter has a Webasto with an output of 5.2kw. He believes his combined capacity of the radiators on Kelly-Louise is also approximately 5kw so theoretically everything should work correctly.
From what I can understand, his Webasto doesn’t have a thermostat but rather cycles on and off by measuring the temperature of the returning water. I assume a thermostat is built into the burner and measures the temperature of the water rather than the atmospheric temperature in their boat.
We planned on Waiouru having a Hurricane diesel heater and that has a capacity of 7.3kw and I did some calculations on the required capacity of the radiators within the boat.
I’d already decided to opt for finrads; primarily because I didn’t want to use wall space for radiators. The finrads can be placed at floor level. I also wanted small heater panels in the base of the wardrobes to keep clothing dry and warm in winter. My calculations looked something like this:
- Hurricane Heater output = 7300w
- Bedroom Radiators in wardrobes (2) = 1200w
- Bathroom Towel Rail (1) = 900w
- Output = 2100w
- Therefore minimum FinRad capacity = 5200w (7300-2100)
- Double Finrad capacity per 492mm = 250w
- Therefore required total minimum length of FinRad = 20 metres
The next problem was to find 20 metres of available linear floor space in a boat that is just over 18 metres long. There is no point in fitting finrads into the back of the galley cabinets, etc. It was immediately obvious the finrads would need to be on both sides of the boat. This has an advantage as it will keep both sides of the boat warm.
So we have planned on finrads in every place where there is open space on the sides of the boat. In addition, I’ve shown a finrad running longitudinally in the storage area under our bed. That will both keep ant thing under the bed dry and warm but also act as a heater whilst we sleep.
I have also considered the consequences of all the radiators being connected on a single ring main. If this were done then it’s possible the first radiator would get very hot working to maximum capacity with very hot water whereas the last radiator would only receive water at a reduced temperature and may not reach maximum capacity. The solution appears to be to create heating zones in the boat; each with their own direct feed pipe from the Hurricane output.
The Hurricane has heating controls for up to four separate space heating zones, each with its own optional thermostat. So we should be able to configure it to maintain different zones of the boat a different temperatures depending upon the time of day.
The 12v DC supply to the Hurricane will be controlled by the Empirbus system. The software program in the Empirbus system will also give us a considerable amount of control over the starting and stopping of the heater. We should be able to send a text message to start the Hurricane if away from the boat and could manage the starting and stopping time of the heater using the timer function within the Empirbus system.
It will be interesting to see if all this theoretical planning can be put into practice.