Boiler Stoves - Usage advice and fuel consumption

Boiler stove fuel consumption

Initially the fuel consumption in the early stages of firing will appear high as the damper will be fully open, allowing a fast burn rate and rapidly raising the heating circuit water to the desired temperature. During the initial stages of firing the return temperature to the boiler will be low having the effect of maintaining a rapid burn rate.

When the whole system is up to working temperature, the return flow water will be high giving only a low differential temperature across the boiler jacket. This will mean the water is up to the desired temperature and the damper will reduce the air to the fire box and the fuel consumption will drop rapidly.

As mentioned in the ‘Boiler over-run’ section, setting the thermostat is important to prevent the boiler from cycling high to low and burning fuel very inefficiently. If a boiler is constantly rising to maximum output and falling back again under damper control, large amounts of fuel are wasted.

During the period when maximum firing is reached and the damper is throttling back the air, a considerable amount of the heat produced will not be absorbed by the water but rather passed directly into the room or up the flue. This is a result of the maximum heat absorption rate of the water being reached before the fire box temperature can fall back under the influence of the damper closing ('control lag').

Best results are obtained with a high quality anthracite fuel, such as Ancit, with around a 20% output to water reduction when burning seasoned hardwood.

Refuelling a boiler stove

The most efficient way to re-fuel the boiler stove is not to continuously top-up with fresh fuel, but rather allow the stove to burn back to a bright ember bed and re-fuel with sufficient fuel for the burn period required. Constantly topping up causes the fire box and flue temperature to fall rapidly as the door is opened and the cold fresh fuel load will use a percentage of the original fuel to heat it to combustion temperature. This will reduce the water outflow temp and cause the damper to open and rapidly increase the burn rate wasting fuel.

Don't operate a boiler stove as a conventional isolated room heater!

All Arada CE approved boiler stoves have only been designed and tested to be used as a dedicated boiler stove as part of a central heating system and not as a purely stand-alone room heating appliance

Therefore, we our boiler stoves should not be used purely as a dry heat stove and can take no responsibility for any resulting problems for being used in such a manner.

Avoiding boiler over-run

Due to the nature of solid fuel boiler stoves in general, the fire box temperature cannot be controlled precisely and once maximum output has been reached, it will take time to reduce the output to water even when the damper is fully closed. For this reason the heat leak radiator and open vent are essential safety features that cannot be dispensed with.

In order to avoid incidents of boiler over-run, opening the thermostat to full and then closing when a desired temperature is reached should be avoided. Set the initial temperature to approximately half way and by trial and error the best position will be found for a consistent temperature level to be obtained. Change the setting in small steps only and wait to see the effect over a period of time.

Bear in mind that Arada boiler stoves have been designed and tested to achieve operational more quickly with solid fuel  than with wood fuel, Once well alight, the boiler will often take between 20 and 40 minutes to produce reasonable amounts of useful hot water. Once the system is up to temperature, the damper will maintain a constant temperature by slowly varying the air supply to the fuel. Avoid constantly changing the primary air control as the output will lag well behind a change to the setting and will result in the output rising and falling in an undesirable way.

What is cold water corrosion and how to avoid it?

This is the result of water below 40°c being pumped through the boiler jacket. This causes large quantities of condensation to form inside the fire box which can encourage rusting but more importantly, mix with the products of combustion when coal is burnt and form a sulphuric acid, attacking the steel work. This can result in a water jacket failure surprisingly quickly.

Solution

We recommend that a pump control pipe thermostat to be fitted on the pumped circuit return flow, set at 45°C disabling the pump until the correct temperature has been reached.

Boiler stove body temperature

The sides, back and top of the stove are surrounded by a water jacket on the boiler stoves and as such will not reach a temperature in excess of the water temperature leaving the stove output ports.

This is quite normal and is designed to preserve as much heat as possible in the water. The majority of heat into the room from the stove will be via the door and glass window.

During the early stages of initial firing, the stove body may feel quite cool even though the fire burn rate is high. This is due to the main volume of heat going to heat the water. It may be necessary to fit a radiator in the same room as the stove to regulate the room temperature more evenly.