How To Keep A Fish Tank Warm Without A Heater: 13 Safe Hacks

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    If you’re looking for advice on how to keep a fish tank warm without a heater because you’re in an emergency situation, feel free to skip right ahead to that section of this article right away because time is of the essence!

    But if you’re here to find out how to bypass the heater long-term when setting-up your aquarium, you’ll probably be surprised just how easily do-able this task is.

    Here are the three main drawbacks when planning to keep a fish tank warm without a heater:

    • you have to take quite a few precautionary steps when setting up your tank;
    • maintaining a constant water temperature in your aquarium will be a much more hands-on task;
    • your options are limited when choosing fish that thrive in a heater-free system.

    No way around these three disadvantages, but that’s not to say that it’s impossible to go heater-free!

    In this article, we’ll go over how to heat up a fish tank quickly without a heater with 13 safe and effective hacks.

    How To Keep A Fish Tank Warm Without A Heater

    how to heat a fish tank without power

    You shouldn’t practice keeping an aquarium warm with no heater when you already have an established, massive tank with tropical fish as inhabitants. That’s a recipe for disaster with more fatalities than you can count!

    These tips will guide you on how to set up a heater-free tank that won’t need round-the-clock effort for stabilizing the water temperature. We’ll discuss emergency situations later on!

    Here are the ways to how to maintain water temperature in fish tank without a heater:

    Use a smaller tank.

    Nano tanks are awesome if it’s your first time experimenting with an aquarium system sans heater. They are quick to heat up and will remain at a constant temperature once established with minimal effort on your part.

    All the methods listed below will work better when used to warm up a tank with a capacity ranging between 3 and 30 gallons.

    In extreme temperatures, or in case of power outages, the water in a smaller tank will get cold sooner, but damage control is a lot more manageable than it is for larger setups.

    Get coldwater fish.

    Coldwater fish are generally hardy fish that not only do well in cooler water but are also resilient to frequent fluctuations in water temperature.

    Fluctuations are deemed to happen when you set up a tank without a heater. So, getting fish that will withstand this common occurrence will only set you up for success later on.

    Coldwater fish need a water temperature that ranges between 60-74°F (20-23°C).

    Turn up the heater in your house.

    This might seem like a common-sense step, but many of us are hard-set on what temperature we keep our home’s thermostat at.

    A good first step to take when trying to keep a fish tank warm without a heater is to bump the temperature in the room where the aquarium is located up to 78°F (25.5°C).

    For some nano tanks, this step alone will get the water temperature to stabilize in a comfortable range for coldwater fish.

    Move the aquarium in a warmer area of your home/closer to a heater.

    There are colder and warmer spots in any home, and that’s something you can totally take advantage of when going heater-free. Setting-up your aquarium in a warmer place will earn you a few degrees with no extra hassle.

    Here’s what you should look for when choosing the ideal location for the tank:

    • A higher level (in a multistory house) – moving your aquarium to a higher level in your home can make a difference of at least a couple of degrees, as upper levels tend to be much warmer.
    • No drafty spots – drafty places tend to run cold, even if you have a central heating system. The cooler airflow might not seem like much, but it can lower the temp in your tank, voiding your efforts.
    • Sunnyside is best – find the area of your home where your tank can get at least 6 hours of natural sunlight per day, and you’ll be surprised how easily a nano tank can warm up with no other input.

    If you choose the warmth-by-sunlight route, have some algae-control solutions on hand, as algae growth can spike when there’s lots of sunlight coming in.

    Use warm water for water changes.

    Frequent water changes using warm water can help you get the tank’s water temperature to the level where you want to maintain it without using a heater.

    The temp will need to be raised slowly, of course. Raising it quicker than 1° per hour can be detrimental to some fish species.

    If you choose this method to warm up your tank, take note that you’ll have to store the extra water needed for the water changes. You can mix room temp water with a portion of boiling water but never add boiling water directly to your tank (even if you don’t have fish in there yet!).

    Insulate the glass walls of your tank.

    Once you get the water temperature in your tank to an acceptable level for the fish you’re planning on housing, insulating the glass walls is a useful next step to consider.

    Covering the back and side-panels of the tank with styrofoam isn’t the most aesthetically pleasing option, but using insulation film or foil is a just-as-good alternative.

    This method will help the existing warmth from escaping, but you may need to continue doing warm-water changes periodically. This is the hands-on drawback that forgoing a heater in an aquarium leads to. 

    Warm up your tank’s water gradually (temporary solution).

    This method works the same way warm water changes do, but it is a lot more finicky. It’s recommended only as a temporary solution when trying to keep a fish tank warm without a heater.

    You can gradually warm up the water in your tank by adding a hot water-filled sealed bottle to your aquarium and letting it float until it’s done its job.

    To put things into perspective, if you’re aiming for an 80°F temp in your tank, the water in the floating container should be at 120°F.

    This isn’t the most efficient option, but it’s still on the table if going heater-free isn’t just a choice but a necessity.

    It does leave room for some pretty drastic fluctuations in water temperature, so you shouldn’t attempt it when housing sensitive fish. Water that’s gradually cooling is less dangerous than huge temp fluctuations.

    Useful Add-ons To Help Keep A Fish Tank Warm With No Heater

    swordtail platy

    There are a few items you can add to your tank system that will eliminate the need for a heater.

    Some of these add-ons require an out-of-the-box perspective, but they’re worth a try if you’re still experimenting with a heater-free aquarium setup.

    Cover the tank with a lid/ hood/canopy.

    Limiting the contact between the water’s surface and a colder airflow using a cover is an easy step to take when trying to keep a fish tank warm without a heater.

    An aquarium lid of any kind will trap warmth and make your other warm-up efforts a lot more efficient. Most tanks can be fitted with tops that are easily removable so you can still have free access to the interior, for feedings, maintenance, and aquascaping.

    Adding a lid can cut back on the water’s oxygen supply, but you can always add an air pump & air stone to help boost oxygenation.

    Use a thermometer to monitor the water temperature regularly.

    thermometer will help you monitor the temperature in your tank and give you a gauge of how well (or not!) your warming-up methods are working.

    At least, when initially setting up your tank, you should keep an eye on the water temperature to see within what range it stabilizes. You’ll have an easier time deciding which fish species would do better in your unheated tank.

    Keep freshwater test kits on hand, too, to see how the temperature influences your tank’s overall water conditions.

    Use stronger lights.

    A lighting system with stronger lights can have the same warm-up effect as setting your tank in direct sunlight. You’ll have more control over how much exposure your unheated aquarium has to light this way. Algae growth can still be an issue in this case, but you can take measures to help with algae-control.

    Keeping the lights turned on for 8-10 hours a day will easily keep a fish tank warm without a heater, especially if we’re talking about a nano aquarium.

    Stronger lights, and the extra heat they give off, will also benefit your plants if you’re working on a heater-free planted tank.

    Add insulation layers.

    Although some aquarists might see this warm-up method as an eye-sore, adding insulation film, or reflective insulation foil, to your setup is the best way to trap-in heat.

    This is an inexpensive and easily accessible add-on that can make a huge difference, especially if your home is particularly drafty or if the ambient temperature goes through significant shifts throughout the day.

    Use a filter that’s not energy-efficient.

    Resorting to using a filter that’s not energy-efficient to keep a fish tank warm without a heater is one of the most out-of-the-box measures you can take.

    Less efficient filtration systems tend to run warm because they use so much extra energy. The filter’s motor can effortlessly heat up the tank’s water quite a bit.

    Pair this up with an insulating add-on, and you could have yourself a hassle-free unheated aquarium.

    Use a heating mat (only for small fishbowl).

    Heating mats are actually made to warm up terrarium/vivarium setups, but they could work for increasing the water temperature in a small fishbowl as well.

    The downside is you would have to add a buffer layer between the heating mat and the bowl’s underside to avoid hot spots and glass cracking.

    Glass isn’t the best heat conductor, so this add-on is one of the least efficient ones.

    This is more of an experimental warming-up method than any of the others listed above.

    Blankets/thick towels if it’s an emergency situation.

    If you want to find a long-term way to keep a fish tank warm without a heater, you’re probably not going to use this “add-on,” but a thick blanket is the best insulating layer you can use in an emergency situation.

    A blanket or thick towel wrapped around the tank’s glass panels can help stabilize the temperature in case of a power outage and make for a slower cool-down. Sudden temperature drops can kill fish, especially those that don’t do well in cooler water.

    Reasons Why You Might Need To Keep A Fish Tank Warm Without A Heater

    Wondering why anyone would go through the hassle of learning how to keep a fish tank warm without a heater? There are plenty of reasons why an aquarist might want to (or have to!) take on this challenge:

    • Power outages – whether they happen often, or they usually last for longer periods of time;
    • Heater malfunctions/replacements – with tropical fish, in particular, keeping the tank unheated while waiting for a heater replacement can do some serious damage;
    • Housing tropical fish – in typically warm areas during unusual bouts of colder weather, when avoiding sudden water temperature drops becomes a necessity;
    • Setting up a quarantine tank – with no budget for an extra heater, especially if it’s an unexpected occurrence (diseased or wounded fish);
    • Extreme temperatures in winter – whether you have an unheated tank or your heater can’t keep up with the drastic change in ambient temperature, extra warmth might become vital;
    • Going for a cordless system – having a cord-free setup can really take aquascaping in a nano tank to the next level, and it’s a totally valid choice if that’s just your personal preference.

    How To Warm Up A Fish Tank Without A Heater In An Emergency Situation

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    Follow these guidelines to keep a fish tank warm without a heater in an emergency situation:

    • Check if your fail-safe measures are active – given you have pre-installed backflow tubing and sump shut-offs in place;
    • Insulate the filtration system first – use blankets, thick towels, or cardboard to wrap it up;
    • Cover the glass panels and top of the tank – preventing the existing heat from escaping a heated tank is essential;
    • Leave some room for oxygenation – don’t completely cut off the tank’s oxygen supply;
    • Don’t check on the fish too often – every time you take off the temporary insulation layers, some of the heat will escape;
    • Use a sticker thermometer to monitor the water temperature – although not the most accurate thermometer, it will let you know if the temp drops dangerously low for the fish inside.
    • Start taking steps to warm up the tank without a heater – if the emergency situation drags on, and the temperature is reaching a dangerous-low, follow the methods listed above to gradually warm up the tank.

    Which Fish Species Are More Sensitive To Water Temperature Fluctuations?

    There are a lot of factors that go into maintaining a constant water temperature in a tank; that’s why most fishkeepers in the hobby can’t fathom setting up an aquarium without a heater.

    Water temp fluctuations, how often they occur, and how drastic they are will definitely restrict the list of fish species you can keep in a heater-free tank.  

    Tropical fish are a big no-no if you’re setting up a tank without a heater. They don’t do well with temperature fluctuations and are prone to diseases when stressed from inconsistent water conditions.

    Here’s a list of tropical fish that need the tank’s temperature to sit within a constant 75-80°F range:

    Neon Tetras Guppies Bushy Nose Plecos
    Congo Tetras Cherry Barbs Swordtails
    Dwarf Gouramis Panda Cory Cat Betta Fish


    • Corals

    Corals need UV lights, specific water parameters, and a constant water temperature to grow and stay healthy. It’s virtually impossible to have a minimalist heater-free system when you plan on setting up a coral reef tank.

    The constant temperature range you need to maintain in this type of aquarium is between 75-78°F.

    Fish Species That Are Resilient To Water Temperature Fluctuations

    Coldwater fish are the only tank inhabitants that won’t mind a long-term heater-free setup!

    These fish species will stay healthy and active in a wide range of water temps and easily withstand significant temperature fluctuations.

    Here’s a list of hardy fish that can thrive in water temps that range between 60-74°F (20-23°C):

    Coldwater fish Water temperature range
    Comet goldfish 60-70°F
    White cloud minnows 64-72°F
    Zebras 70-78°F
    Paradise fish 60-86°F
    Variable platy fish 61-75°F
    Rainbow shiners 60-80°F
    Hillstream loaches 68-75°F
    Endler’s livebearers 64-84°F
    Clown killifish 68-79°F
    Cherry shrimp 57-84°F
    Dojo loaches 68-76°F

    FAQs About How To Keep A Fish Tank Warm Without A Heater

    How To Keep Betta Fish Warm Without A Heater?

    To keep betta fish warm without a heater, you can use alternative methods such as using a heat lamp or placing the fish tank near a heat source like a radiator.

    Additionally, insulating the tank with blankets or wrapping it in bubble wrap can help retain heat.

    Monitoring the water temperature regularly is crucial to ensure a comfortable environment for your betta fish.

    How To Keep A Fish Tank Warm Without Power?

    To keep a fish tank warm without power, there are a few methods you can try.

    Firstly, insulate the tank with blankets or foam to trap heat.

    You can also place the tank near a source of warmth, like a fireplace or sunlight.

    Lastly, using warm water during water changes can help maintain the tank’s temperature.

    What Fish Don’t Need A Heater?

    Several types of tropical fish can thrive without a heater in English aquariums.

    Some popular options include Betta fish, Guppies, White Cloud Mountain Minnows, and Zebra Danios.

    These species are known for their ability to adapt to varying water temperatures, making them suitable for tanks without a heater.

    How To Keep A Fish Tank Warm In A Cold Room Without A Heater?

    To keep a fish tank warm in a cold room, there are a few effective methods.

    Consider insulating the tank with a foam or insulating material, placing the tank near a heat source, or using a temperature controller.

    Monitoring the water temperature regularly is crucial to ensure the well-being of your fish.

    What Temperature Should A Fish Tank Be?

    The ideal temperature for a fish tank typically ranges between 75 and 80 degrees Fahrenheit (24-27 degrees Celsius).

    Of course, this is just general advice, and the temperature requirements of your fish may vary depending on the species.

    Maintaining the correct temperature is crucial for the health and well-being of your aquarium fish, as it can directly impact their metabolic functions and overall behavior.

    How To Heat Up Fish Tank Water Quickly?

    To heat up fish tank water quickly, start by adjusting the aquarium heater to the desired temperature.

    Increase the water temperature gradually to avoid shocking the fish.

    Use a portable heater or a heat lamp as additional heat sources.

    Ensure the heater is safe for aquatic use and closely monitor water temperature throughout the process.


    Whether you want to, or you have to, you can definitely find efficient ways to keep a fish tank warm without a heater. It’s up to you to decide if it’s worth the hassle to keep this setup long-term!

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