Insulating a brewing kettle conserves heat and saves energy. I personally find it difficult to take such a beautiful, shiny piece of stainless steel equipment and wrap it in a dull mantle, but then again I am mostly a proponent of "function over form".
Updated on June 29 2021 to include Neoprene as an insulating option
Insulating a kettle provides the following benefits:
- Energy Savings
- Increase in the volume of wort one can effectively heat and boil with a given heat source
- Minimization of heat loss through the kettle wall - especially important during mashing
While I would not recommend insulating a kettle using a gas-fired heat source, or maybe only using a fiberglass based wool insulation for that, I see little or no reason not to insulate a kettle in an electric brewery.
Armaflex
When I looked into different types of insulation, I quickly focused in on the option that many brewers in Europe already have experience with: the closed cell foam sheet product commonly sold under the Armaflex AF brand name. I did not consider the foil/bubble style sheet insulation, widely sold as Reflectix in the USA, as its availability is limited here in Europe. Another option certainly worth mentioning is a sleeping bag or blankets - this is the most economical and readily available option, and also works well!
What thickness to use? The 25 mm and greater thicknesses interfere significantly with the Tri Clamp connections making them very difficult to use while the kettle is wrapped. The 19mm thick material was useable, but makes it difficult to tighten clamps without tearing into the insulation with your fingernails. the 13mm Armaflex allows better access when making Tri-Clamp connections, so I decided to test the performance of the 13mm and 19mm versions.
Neoprene
(Update - June 29 2021)
Recently I noticed other manufacturers offering Neoprene jackets for their brew kettles. I've seen neoprene used more commonly in the fermentation cellar and for beer kegs. Neoprene looks clean, is relatively easy to manufacture into zippered jackets, and can be printed with a logo. It looks great! But how well does it work for kettle insulation? Commonly found in 5 mm thickness, I built a 5mm prototype for testing purposes.
Test Results
Brew kettle used in insulation test.
To test the insulating capabilities of these products, I used a 57 Liter Craft Hardware kettle and heated 25 L of water to 61,5 C. The test was performed in a ventilated room with temperatures steady around 19 C and no wind. Temperature was measured over 60 minutes using craftbeerpi as a data logger. The hot water was recirculated through a whirlpool arm to avoid erroneous temperature readings due to stratification. The temperature probe was located in a Tee fitting just past the kettle output valve. I wrapped the valves, pump, clamps, and return hose with a combination of materials to minimize the heat loss through the external circuit.
First I performed a baseline test of an uninsulated kettle with the lid on, and then performed three more tests by wrapping the kettle completely with Armaflex in 13mm, Armaflex in 19mm, and neoprene in 5mm thickness. This included a disc cutout of the same material to cover the lid.
As shown in the chart, the total heat loss over 60 minutes for the uninsulated, 5mm Neoprene, 13 mm Armaflex, and 19 mm Armaflex versions was 4.6, 3.6, 2.3, and 2.1 degrees C respectively.
The thicker Armaflex insulates much better than the thinner neoprene, and the difference between the 13mm and 19mm Armaflex thicknesses was surprisingly small. Armaflex is sensitive to tearing by fingernails and tends to stick to the kettle when it gets wet. You may need to replace it every year or two if you want it looking in top condition. But it simply performs much better than other options, so if that is important to you it's a great solution. Neoprene looks fancy and is more durable, but just doesn't insulate quite as well as other options.
For those looking for a commercial product, the Craft Hardware kettle insulation provides a custom fit three piece insulation kit using the 13mm thick Armaflex AF sheet and a special glue manufactured specifically for this product, the combination of which is rated up to temperatures of 105C.