Manually Generate Heat in Your Aquarium If the Power Goes Out

Keep Your Fish Warm in Cold Weather Conditions

Aquarium with fish

John Verive/Flickr/CC BY-SA 2.0

When the power goes out and you do not have an emergency power source to run your tank heater, there are a couple of things you can do to help keep the aquarium's water temperature from dropping to hazardous levels. This is especially important if the outage occurs during cold weather days.

Of course, the objective is to keep your tank within the optimal temperature range, but at this point keeping the temperature even close to it will be satisfactory. Ideally, you will have prepared for a power outage, but that does not always happen. There are ways to help your tank retain what heat it does have and to add heat to keep it where it should be.

Retain the Existing Heat

The first thing to do when the power goes out is to quickly take steps to retain the heat that is already in the aquarium. Heat rises and ​newspaper has amazing insulation properties. By wrapping the outside of the tank with thick layers of newspaper, covering the top and blocking off any hood vents, you can prevent heat from rising and escaping from the aquarium. In all likelihood, you will not be running the aquarium lights, but if you have a power source to do so, do not cover the light hood, which is a potential fire hazard. If you do not have newspaper, towels or a blanket can be used.

Manually Generate Heat

Once steps have been taken to retain the existing heat in the aquarium, look at how you can begin generating heat to keep the aquarium warm.

  • Boil water with anything you have available, such as a portable propane camping or hiking stove, wood, charcoal, or a propane grill.
  • Pour the boiled water into any type of sturdy plastic container that can be tightly sealed, and more importantly, will not melt due to the high temperature of the water. This method was tested using clean one-gallon bleach jugs, and it worked fine.
  • Place the hot water-filled container in the aquarium and let it float. When the container starts to cool off, refill or replace it with a newly-filled one.


  • Depending on the size of your aquarium and the ambient room temperature, you can use more than one floating container.
  • The water level may rise when you add containers, so remove some water from the aquarium.
  • Add a drop of dechlorinating solution in the container as a safeguard against container water leakage.
  • A good way to circulate the water throughout the aquarium is to pour aquarium water over the container, which is also a way to generate oxygen manually.