Brew Kettle Insulation

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”.

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.

The Armaflex solution

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 it’s 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!

But for those looking for a commercial product, the Craft Hardware kettle wrap 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.

Why 13mm thickness? Well the 25 mm and above 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. If you are very careful about tightening your fittings, you can use the 19mm Armaflex without tearing it every time. But what is the actual benefit of the 19mm vs the 13mm thicknesses? I put them to the test.

13 mm vs 19 mm

Brew kettle used in insulation test.

To test the insulating capabilities of these two 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 the following 60 minutes using my one-wire craftbeerpi controller. I decided to recirculate the water in the kettle to avoid erroneous temperature readings due to stratification, and placed the temperature probe just past the kettle output valve in a tee fitting. I provisionally wrapped the valves, pump, clamps, and return hose with a combination of materials to minimize the heat loss through the external circuit. This external insulation remained the same for all 3 tests.

I performed a baseline test of an uninsulated kettle with lid on, and then performed two more tests by wrapping the kettle completely with armaflex, including the lid, using 13 mm and 19 mm thicknesses respectively. As shown in the chart, the total heat loss over 60 minutes for the uninsulated, 13 mm insulated, and 19 mm insulated versions was 4.6, 2.3, and 2.1 degrees C respectively.

Chart showing results of insulation test.

The difference between the 13mm and 19mm thicknesses was surprisingly small, so I went with the 13mm version to increase the longevity of the product without a significant sacrifice in performance.

It’s worth noting that performance of the product in “real world” conditions will vary, i.e. if it is very cold or very windy the 19mm may perform more efficiently than 13mm. The 13mm armaflex insulation is a good option, if you want to insulate your kettle while providing easy access to the ports and fittings.