Stage 2 - Design - Heating System

For properties which are completely off grid heating options are often limited as any form of electric renewable heating such as air source heat pump or ground source is not usually an option as the electrical demand for these this type of heating is just too high to be viable. In Josh’s case when he took over Crashpad the property already had a 14.4kW Biomass hand fed wood pellet boiler installed, when this boiler was running it managed all the heating/hot water demand perfectly so in that case we already had a good idea of what size of biomass boiler was needed, Josh wanted to stick to heating with wood pellet as it maintained the buildings eco credentials and he was already experienced with running a biomass heating system such as regularly topping up with pellet & clearing the ash box, Josh also liked the fact that once a pellet boiler is full it works more or less like a standard oil boiler saving the guest interaction needed with a more traditional log burner so the guests can just relax & get on with their holiday in comfort

Even though we already had a good idea of the heating & hot water demand for the property from the existing biomass system it’s always good practice to carry out a heat loss which we use computer software to calculate, plugging in the buildings measurements, insulation levels & any relevant information, even the properties height above sea level is taken into account, this then gives us a figure in kW which we can use to size the preferred heating system.

Unfortunately Josh’s existing pellet boiler which was around 10 years old had broken down & had water damage; our site survey also revealed some major issues with the positioning of the boiler, mainly the pellet boiler was placed next to the battery bank! This meant we had to condemn the existing biomass on health & safety grounds as it is extremely dangerous to have a naked flame anywhere near a flooded lead acid battery bank. Josh decided that taking into account the age of the existing boiler and the significant water damage that the best option was to have a new pellet boiler installed.

We went with a 15kW ETA automatic fed wood pellet boiler which we recommended be placed in its own plant room away from the battery bank. This could happily take care of all the bunkhouse’s heating & hot water on its own however Crashpad also benefits from an existing Solar thermal array which will reduce the demand on the pellet boiler in the summer months.


The existing tank is only 250Ltrs in capacity & undersized for the potential demand of domestic hot water within the property (i.e. 18 muddy walkers all wanting a shower after trekking up Snowdon!) so it was decided that we would replace the existing DHW tank with a 500ltr buffer/thermal store. This will provide both DHW through a stainless steel heat exchanger and the flow and return to the underfloor heating system. Using a buffer also increases the efficiency of the boiler as it stops any short cycling (for more info on short cycling read our off grid heating blog) therefore allowing it to burn for longer. As a bonus, the ETA boiler can also control the solar thermal system meaning further overall system efficiencies.


Now that we have all the designs in place for the  electrical & heating systems the next stage is getting the kit to site, with Crashpad being positioned half way up Snowdon this could prove to be interesting….!

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