One way of reducing energy consumption in residential and institutional buildings such as schools and hospitals is by use of a tubular biogas digester. Use of biogas eliminates the use of the more expensive electricity and/or liquefied petroleum gas (LPG). Organic materials are the feedstocks for a biogas system. Some organic materials will digest more readily than others. Restaurants fats, oils and grease; animal manures; wastewater solids; food scraps, and; by-products from food and beverage production are some of the most commonly digested materials. A single anaerobic digester may be built for a single material or a combination.