DIY Energy-Efficient Fridge

Traditional fridges and freezers are massive energy hogs, even the “energy star” ones. Building your own energy-efficient system is not only possible — it can save you thousands of watt-hours.

Here’s how to do it:

Start with a Chest Freezer​
Most DIY off-grid fridges and freezers start with a basic chest freezer — and for good reason. Chest freezers are better insulated than upright models and lose far less cold air when opened (because cold air sinks). Look for a small to medium model (5–10 cubic feet). They’re affordable and easy to modify.

Install an External Temperature Controller​
The magic trick to turning a chest freezer into a super-efficient fridge is an external thermostat controller. These devices plug into your freezer and monitor the internal temperature. Once your set temperature is reached (say, 35°F for a fridge or 0°F for a freezer), it cuts power. The compressor only runs when absolutely necessary, slashing your energy use by 60–80%.

Good controllers to look for: Inkbird ITC-308 or Johnson Controls A19.

Wiring Diagram from Johnson Controls

Fine-Tune Your Settings​
If you’re using the chest as a fridge, set the external controller to around 35°F–38°F. It may take a few days of tweaking to find the sweet spot between food safety and minimal run-time.

Pro Tip: Chest freezers in fridge mode usually only run about 15 minutes every couple of hours — extremely efficient compared to traditional fridges!

Boost Insulation​
Even new chest freezers can benefit from a little extra insulation. Wrap the outside with foam board insulation (R-10 or higher), especially if you’re in a hot climate. Secure it with industrial-grade tape or strapping. Every extra inch of insulation reduces compressor cycles and saves you battery life or generator fuel.

Mind the Placement​
Place your fridge/freezer in the coolest possible part of your home — like a north-facing corner or a shaded shed. The cooler the surrounding air, the less your system has to work to maintain its internal temperature.

Solar? Think DC​
If you're running purely on solar, consider a DC-powered chest fridge/freezer, like models from Sundanzer or Dometic. These are built from the ground up to be miserly with power and run directly off 12V or 24V battery banks, avoiding inverter losses. They cost more upfront but can double the life of your battery bank over time.