Oase

BioMaster Thermo 850 an external filter that includes a heater it to both filter and heat a large fish tank
BioMaster & Thermo External Filters
BioMaster & BioMaster Thermo external filters by Oase are suitable for large aquariums. If you click 'yes' to a heater, this filter will come with an Oase HeatUp heater installed. If you choose 'no' to the heater, a HeatUp can be added later on, and fits neatly into the filter. See below for details of the heater wattage needed. HeatUp by Oase is the only recommended heater for use with this filter. The pump is energy efficient and quiet.
not rated Price range: £229.99 through £374.99 Select options This product has multiple variants. The options may be chosen on the product page
An external fish tank heater by Oase, FiltoSmart 300
FiltoSmart & Thermo External Filters
FiltoSmart and FiltoSmart Thermo 300 by Oase are external filters suitable for medium to large aquariums of 300 litres volume or less. The pump is energy efficient and quiet. If you choose the Thermo version, the heater is neatly installed into the filter and fully controllable so that you can choose the best temperature for your fish.
not rated Price range: £154.99 through £179.99 Select options This product has multiple variants. The options may be chosen on the product page
Oase HeatUp aquarium heaters, if you are wondering, what heater should I use for my fish tank? These are one of the best heaters because they can run inline if you have an Oase FiltoSmart, BioMaster or BioPlus filter you can turn it into a Thermo internal or external filter
Oase HeatUp
Oase HeatUp aquarium heaters are a range of high precision fully submersible heaters suitable for any type of aquarium. They can be used as sand alone heaters or run inline inside one of Oase's BioPlus internal, or Oase's FiltoSmart or BioMaster external filters.  
not rated Price range: £24.99 through £39.99 Select options This product has multiple variants. The options may be chosen on the product page