BRUNNER stove upgrade sets are intended for replacing old stove inserts, when the owner’s wish is to use it as a supplementary heating system in future. Because the heat exchangers of B7 and B8 models do not require any cleaning, these boiler types are maintenance-free. Of course both water heaters can be recommended for new stoves with an expected boiler power rating of 33- 40%. Boiler type B7 has a rated heating load of 6 kW, whereas the B8 can provide 8 kW max.