Aquarium heaters are a sure-fire way to provide stable water temperature in aquariums that house tropical fish or fish that are sensitive to temperature fluctuations.
There are many types and brands of heaters on the market, and it’s easy to get lost in the process of searching for one, especially if you’re looking to find the best heater for your aquarium.
By reading my article on this topic, you’ll understand the importance and role of a heater, you’ll know what to look for in a heater, and you’ll have an overview of the best aquarium heater options currently available on the market.
Why You Need a Water Heater in Your Fish Tank?
When setting up a fish tank, you’ll need to do your best to recreate the natural environment of your fish, and this includes getting their temperature range just right.
Keeping your fish at lower temperatures than what they’re used to or exposing them temperature fluctuations will bring about health issues or it can even be fatal for them.
An aquarium heater will help you control the temperature of their environment and help stabilize it, so it isn’t affected by fluctuations in air temperature.
Although a heater is not always necessary (e.g. you’re not likely to require a heater if you live in a tropical climate), in areas where outside temperatures fluctuate from seasons to season, an aquarium heater is a must if your fish enjoy warmer water. If you keep guppies or other tropical fish, most likely you will need a heater.
How to Choose a Water Heater for Your Aquarium Size?
The water volume of your aquarium will be the determining factor in choosing the right aquarium heater size.
There are some generally accepted rules like the 5 W per gallon rule, which you can use to approximate the heater size. This table will help you determine the heater size for your aquarium water volume.
| Tank Size | Heater Wattage |
| 5 Gallon / 20 Liter | 25 W |
| 10 Gallon / 40 Liter | 50 W |
| 20 Gallon / 80 Liter | 100 W |
| 25 Gallon / 95 Liter | 125 W |
| 40 Gallon / 150 Liter | 200 W |
| 50 Gallon / 190 Liter | 250 W |
| 65 Gallon / 250 Liter | 2 x 200 W |
| 75 Gallon / 285 Liter | 2 x 200 W |
| 80 Gallon / 300 Liter | 2 x 300 W |
| 90 Gallon / 340 Liter | 2 x 300 W |
| 100 Gallon / 380 Liter | 2 x 300 W |
The above table should be taken only as a guide and it works only for certain conditions. If the air temperature is 70 °F (21 °C), you will be able to heat the aquarium water to up to 80 °F (27 °C).
You should also pay close attention to the manufacturer’s product description to determine if your heater will be right for your aquarium size.
It’s also a good idea to read up on product reviews to see if the heater you’ve set your eyes on is indeed as strong and efficient as advertised.
Best Aquarium Heaters
| Preview | Heater Name | |
|---|---|---|
 | 1. Eheim Jager Aquarium Thermostat Heater | |
 | 2. Fluval E Electronic Heater | |
 | 3. Cobalt Aquatics Flat Neo-Therm Heater | |
 | 4. HITOP PTC Submersible Aquarium Heater | |
 | 5. Aqueon Adjustable Aquarium Heater | |
 | 6. FREESEA Aquarium Fish Tank Heater | |
 | 7. Boxtech Submersible Aquarium Heater | |
 | 8. UPETTOOLS Submersible Aquarium Heater | |
 | 9. Hygger Titanium Aquarium Heater | |
 | 10. Hydor Submersible Glass Aquarium Heater |
Below you can read a short overview of the best water heaters for aquariums, and the pros and cons of each:
1. Eheim Jager Aquarium Thermostat Heater
This Eheim Jager aquarium heating equipment is a complex and complete system for ensuring proper water temperature for your fish.
The product is available in 8 different wattage sizes for you to pick the size that’s required for the water volume in your aquarium.
The heater is fully submersible and comes with many features that enhance temperature control and safety including:
- Shock-resistant and shatter-proof glass (suitable for both marine and freshwater applications);
- TruTemp dial allows you to set the temperature between 65° to 93° F;
- Running dry protection through the Thermo Safety Control feature;
- Mounting bracket and suction cup for easy and flexible installation;
- On/Off indicator light;
- Heater control accuracy is +/- 0.5° C;
- 6-foot cord;
- Simple and safe recalibration.
As I mentioned, the Eheim Jager heater comes with all the basic features you need from a competent aquarium heater.
Pros:
- Adjustable temperature;
- Accurate heater;
- Easy installation;
- Running dry protection.
Cons:
- Some malfunctions reported by customers, best be used with a temperature controller.
2. Fluval E Electronic Heater
Suitable for aquariums of 30 gallons and more, the Fluval E electronic aquarium heater provides real-time and precise aquarium readings thanks to the dual temperature sensors.
The system features an LCD temperature display, which is available both in Celsius and Fahrenheit as well as a high/low temperature alert feature that will flash in a different color should temperatures fall below or exceed a preset temperature value.
You can fully submerge this Fluval aquarium heater, which is equipped with a slim profile mounting bracket for easy installation. You can mount the heater either horizontally or vertically, however it fits best in your aquarium.
The fish guard protection of the Fluval heater protects your fish when getting into contact with the core of the heater. The protection of the glass sleeve is also useful for protecting the glass itself from larger fish.
Overall, this heater is a good choice for the aquarium sizes it’s rated for. Be sure to mount it at a 45-degree angle to get if working perfectly for you.
Pros:
- Dual temperature sensors for accurate temperature reading and control;
- LCD temperature display;
- Fish guard protection;
- High/low temperature alert.
Cons:
- It takes a couple of days to heat up the water.
3. Cobalt Aquatics Flat Neo-Therm Heater
I really like the flat design of this submersible heater from Cobalt Aquatics. You can get the heater in six different size configurations for aquariums between 6-55 gallons.
You can install the heater to face inward or outward thanks to the reversible holster/bracket for more control over the installation and positioning.
The temperature can be set between 66-96° F with one touch and the in-built thermostat will keep the temperature at the set level with a temperature variation of +0.5°F.
For easy temperature monitoring, the heater features and LED display, which shows both set temperature and actual temperature at the same time.
Another useful feature of this heater is its built-in automatic shut-off system, which turns off the heater, preventing it from overheating.
A further novelty of the Cobalt Aquatics flat neo-therm heater is the materials it’s made of. The outer casing is a shock-proof, shatter-proof material.
The heater comes with a 3-year warranty, it’s suitable for both freshwater and marine applications.
Pros:
- Adjustable temperature;
- Thermal protection circuitry protects from overheating;
- 3-year warranty;
- Shatterproof design;
- Flat design and easy installation.
Cons:
- Requires water flow to work efficiently;
- Some customers experienced system malfunctions but were covered by 3-year warranty.
4. HITOP PTC Submersible Aquarium Heater
A fully submersible aquarium heater, the HITOP PTC features titanium oxide ceramic heating material, which is safer compared to glass-type heating elements.
The 300 Watt heater is suitable for 60-120 gallon aquariums. The heater element must be completely submerged to avoid damage to the heater.
The heater also features a detachable casing and comes with 4 suction cups for easy fixing.
The heater indicator light takes out the guesswork from knowing when the heater is operating.
The temperature can be adjusted with a knob on top of the heater. Once the preset temperature is reached, the heater shuts off.
My only concern with this heater is the grated design of the detachable cover, which has even bigger holes on the sides, which would allow baby fish or even small adult fish to get into the cover and potentially getting trapped into it, so I don’t recommend it for aquariums with baby fish.
The temperature can be set between 60 and 93 F and the temperature is also displayed in Celsius.
The heater kit comes with a stick-on thermometer for you to monitor temperature changes.
Pros:
- Adjustable temperature;
- Shatter-resistant materials;
- Easy to install and maintain.
Cons:
- Detachable protective cover has large side holes that will let fish get in;
- No running dry protection.
5. Aqueon Adjustable Aquarium Heater
Available in a variety of different sizes, the Aqueon offers adjustable temperature control (you can set temperature between 68° to 88°F and it features a shatter resistant thermal quartz glass as its heating element.
The Aqueon heater can be installed vertically or horizontally with the suction cups included with the product.
The automatic safety shut off system jumps into action whenever the heater is not fully submerged to protect from overheating and damage.
Another feature worth noting is the power monitor, which is red while the heater is actively heating the water and turns green once the set temperature is reached.
Overall this heater offers good value for money, comes good features that will provide stable temperatures.
Make sure to choose the right wattage for your tank to avoid performance issues.
Pros:
- Provides good value for money;
- Adjustable temperature;
- Overheat protection;
- Vertical or horizontal installation;
- Automatic safety shut off
Cons:
- Requires stronger water flow for perfect operation.
6. FREESEA Aquarium Fish Tank Submersible Heater
Available in sizes rated for up to 50 gallon tanks, this aquarium heater should be kept fully submerged to protect from overheating.
This means you should monitor the water level to make sure it stays within the accepted threshold.
The features that make this heater stand out are the following:
- Small, space-saving design;
- Real-time LED temperature display;
- Adjustable temperature between 59 F and 93 F;
- Equipped with protective plastic casing.
The temperature control box is not water resistant, so make sure to keep it out of the water.
On the other hand, the heater should be submerged as it doesn’t have an overheating shut-off system.
The heater comes in various sizes suitable for 5-50 gallon aquariums.
The automatic constant temperature function shuts off the heater when predefined temperature is reached, but it automatically starts heating when it drops below the set temperature.
The product comes with a 12-month warranty.
Pros:
- Adjustable temperature control;
- Small, compact design;
- Real-time temperature display.
Cons:
- No running dry protection;
- The holes on the protective casing may make it easy for small fish to get stuck in the coils.
7. Boxtech Submersible Aquarium Heater
Featuring a simple design and installable via suction cups, the Boxtech Submersible Aquarium heater comes in different sizes and works with aquariums up to 80 gallons, therefore, you must choose the correct wattage for the size of your aquarium.
The heater comes with an external temperature controller that stops the heater from heating the aquarium when the set temperature is reached and starts the aquarium when the water temperature falls below the set temperature.
The temperature is adjustable and can be set in the 68ºF-90ºF range. The heater has an explosion-proof design thanks to the heat-resistant milky quartz glass. This coupled with the UL-Approved Power Cord, Controller IPX4, Heater IPX8 make the system shatter-proof and safe.
The Boxtech heater must be submerged into water and installed close to the water intake or next to the water flow. The heater requires horizontal installation via the provided anti-slip silicone suction cups.
Anyone looking for a compact and efficient heater will surely enjoy this Boxtech product provided they choose the right size for their aquarium.
Pros:
- Compact and easy to install;
- Precise with temp variation within 0.5 degrees;
- Explosion and shatter-proof.
Cons:
- No running dry protection.
8. UPETTOOLS Submersible Aquarium Heater
With sizes ranging from 50 Watts to 500 Watts, Upettools submersible aquarium heaters are rated for aquariums between 3-120 gallons.
The heater element is made of durable and explosion proof quartz material. It also features a protective cover. The heater comes with a 1-year warranty.
The dual CPU external temperature control allows you to adjust the temperature and shuts off/turns on the heater depending on temperature changes. There’s also an indicator light on the heater that signals when the heater is on or off.
Temperature range is between 75-89 F. The heater must be installed horizontally, and it should not be buried under gravel or sand. It should have access to water flow.
According to the description of the manufacturer this heater is suitable for both saltwater and freshwater tanks, but it’s not recommended to be used in acrylic or plastic tanks.
The heater comes highly recommended, however, there are a few drawbacks to consider.
Pros:
- Good design, easy installation
- External temperature controller
- Adjustable heater
- Automatic shut-off
Cons:
- No running dry protection
- Not suitable for plastic or acrylic tanks
- Must be installed horizontally (vertical installation not allowed)
9. Hygger Titanium Tube Submersible Pinpoint Aquarium Heater
This Hygger submersible aquarium heater takes things up a notch by rolling out a heater made of heavy-duty, durable titanium without any glass elements whatsoever.
Because of its titanium construction, the heater is corrosion resistant, completely shatterproof, and it can be used in saltwater, freshwater, and reef tanks.
Regarding installation, the heater installs horizontally with the help of suction cups. Ideally, it should be placed near strong water flow, so it heats up the entire aquarium at the same temperature.
While the titanium construction of the heater element is of superior quality, I’d also like to draw attention to the external temperature controller, which is also a great feature of this product.
This external thermostat has a dual LCD display that shows the set temperature and the actual temperature of the water. You can set it to display temperature in either C or F. The red/green light signal shows whether the heater is operating or not.
The temperature range is 32 to 104°F. Control accuracy is +/- 0.5° C. The heater is not suitable for sump tanks, acrylic or plastic tanks, nor can it be used outside.
Pros:
- Titanium construction makes this heater a strong and durable option
- Adjustable temperature
- Real-time temperature display
- No glass elements whatsoever
Cons:
- Horizontal installation only
- Costs more than traditional glass or quartz heaters
10. Hydor Submersible Glass Aquarium Heater
This Hydor glass aquarium heater is an affordable heater option that doesn’t come with many bells and whistles but does the job right.
It’s available in 5 sizes (25 to 200 Watts), and it must be installed completely submerged, either vertically or horizontally.
Even though it’s not as feature rich as other heaters in this list, it does have running dry protection, which is useful if you should forget the switch it off during water changes or if water levels in the tank drop.
Temperature can be controlled with the help of a graduated scale that shows temp in F or Celsius. The heater is built for resistance and has a shatter-proof design.
Make sure to pick the right wattage number for the aquarium size you have and monitor the temperature with an external temperature controller as well.
Pros:
- Easy to install via suction cups (vertically or horizontally)
- Adjustable temperature control
- Affordable
Cons:
- Some customers reported issues with the temperature dial being faulty
There are many heater options available on the market, the key is to find the one that meets your requirements and works with the aquarium size you have.
When picking out your heater, I strongly encourage you to read the reviews and see how the heater performs and whether there are any concerns related to their operation and quality.
Conclusion
In your search for the best aquarium heater, I hope my article has provided you with useful information that you can apply right away.
Aquarium heaters all not all made the same, there are many variations in features and operation, so make sure you make an informed decision whenever buying one.
I hope the 10 best aquarium heaters I listed in this article have given you an idea about the features that a heater must have and best way to install them.
Updated: November 27, 2019
FAQs
What size heater do I need for a 100 gallon tank? ›
For the heater wattage, the basic rule of thumb is to use between 2.5 and 5 watts per gallon of actual water volume in the aquarium.
What is the most efficient aquarium heater? ›Best Aquarium Heater Winner: Fluval E200
The Fluval E200 is the best aquarium heater and also the most accurate and safe. Out of the heaters I tested, it was the set-it-and-forget-it model.
Confusion Over 25-Watt Heaters at the Store
It got so confusing and frustrating! On the market, there are 7.5w, 10w, 15w, 25w aquarium heaters—all indicating that they will work just fine for a tank 5 gallons and under. BEWARE! Not all low-wattage heaters are the same!
A good range is 76° to 80°F (25° to 27°C). A few species need to be kept several degrees warmer, and some species require temperatures a few degrees cooler. A thermometer is vital. A stick-on type enables you to check the temperature whenever you look at the aquarium.
How many watts do you need for a 100 gallon tank? ›A normal 100 gallon tank can benefit from a powerhead with a flow rate of 686 GPH and power consumption of 4 watts.
How long does it take for a 100 gallon water heater to heat up? ›Here are some common heat up times for different water heaters, assuming the appliances are new and properly sized for the home: Electric storage tank water heater: 60–80 minutes. Propane storage tank water heater: 30–40 minutes. Propane tankless water heater: 0 minutes.
What brand of tank water heater is the most reliable? ›- Rheem Gladiator Water Heater. The Rheem water heater is a durable and reliable water heater that has a fantastic 12-year warranty. ...
- Westinghouse Lifetime Electric Water Heater. ...
- Rheem Performance Platinum Smart Electric Water Heater. ...
- A.O Smith Signature Gas Water Heater. ...
- Bosch Tronic 3000 T ES4 Water Heater.
- Best Controls: Stiebel Eltron Electric Tankless Water Heater.
- Best Gas Tankless Heater: Rinnai Gas Tankless Hot Water Heater.
- Best Point-of-Use Heater: Bosch Electric Mini-Tank Water Heater.
- Best Electric Tankless Heater: EcoSmart Electric Tankless Water Heater.
Do not use an oversized heater – if it malfunctions, it can quickly change the water temperature and harm or kill your fish. For larger tanks (55 gallons and over or so), I'd recommend using 2 smaller heaters. This greatly reduces the chance of harm to aquarium inhabitants should one heater fail.
Is a 50 watt heater too big for a 5 gallon tank? ›Recommended is 3–5 watts per gallon so with a fifty watt heater around 10 to 15 gallon tank. You could use a smaller tank but that would mean more sudden temperature shifts as the heater cycles.
How many watts is a good heater? ›
750 watts works well for a small office, small bedroom, or bathroom. 1000 watts should warm up large bathrooms, small living rooms, or a small room. 1500 watts will heat spaces up to about 150 square feet and can help you stay warm and toasty in a medium-sized room, office, kitchen, or modest-sized living room.
How many gallons does a 100 watt heater use? ›A: A 100 watt heater can raise a 20 gallon tank 15 degrees above room temperature.
How do I know if my tank is too cold? ›If your tank temperature is too cold, then your fish's metabolism will slow down, which leads to your fish becoming sluggish and sleepy. On the flipside, water that is too warm causes your fish's metabolism to speed up. Your fish will become more lively or even hyperactive.
How often should I change my 5 gallon tank? ›You should do a 25% water change every two to four weeks. There is no reason to remove the fish during the water change. Make sure you stir the gravel or use a gravel cleaner during the water change.
How many fish can I have in a 5 gallon tank? ›You can keep about 2-4 fish in a tank this size as long as each fish is not larger than 1 inch. The one-inch fish per gallon rule would apply to most smaller fish breeds like Tetras, Betta, Rasbora, Shrimps, and more. Fish that can grow larger than 1 inch are not recommended for a 5-gallon tank.
What filter do I need for a 100 gallon tank? ›A filter with a flow rate of at least 300 GPH should be able to filter your 100-gallon tank three times in an hour. Faster flow also helps with faster air circulation.
What temperature should my aquarium heater be set at? ›Most tank fish do well at temperatures from 75-80 degrees Fahrenheit (23-27 degrees Celsius), but the needs of specific fish can vary. If your tank is home to just one or two types of fish, it is best to investigate their preferred temperature range and take steps to keep your tank in the middle of that range.
Should I have 2 heaters in my aquarium? ›There are some distinct advantages to having more than one heater in an aquarium. If the room that the aquarium is in is quite cold and the aquarium water temperature drops and a single heater can not raise the temperature, a second heater would help boost the heat produced to raise the water temperature.
Does turning up water heater make hot water last longer? ›Turn up the thermostat on the hot water heater. One of the easiest ways to make a hot shower last longer is by using less hot water while it's at a higher temperature. To do this, turn up the temperature on the thermostat that's attached to the hot water heater tank. (Not the thermostat on the wall.)
How long does a 100 gallon water heater last? ›With regular inspection, draining, and flushing, you can expect a gas water heater to last anywhere from 8-12 years and an electric water heater to last anywhere from 10-15 years.
How long can water sit in water heater? ›
Most homeowners should flush their water heaters every six months or so, but if you have extremely hard water, you may want to do it more often.
What is the number 1 hot water heater? ›1. Rheem Marathon Electric Heater — 9.2/10 (Overall best electric water heater) The Rheem Marathon Electric Water Heater kicks off this list as the best electric water heater that money can buy because of its extended lifespan, lifetime warranty, and energy-saving features.
What is the number one hot water heater? ›Our best overall picks are the Rheem Performance 40 Gal. Natural Gas Tall Water Heater and the Rheem Performance Plus 50 Gal. Electric Water Heater, both of which offer large capacity, durability, and longevity.
Which water heater lasts the longest? ›A tankless water heater can last up to 20 years, sometimes even longer. Also called “on-demand” water heaters, these appliances do not work continuously to maintain a supply of hot water—and, as a result, they last longer than their tank-style counterparts.
What is the best water heater in the world? ›- AO Smith 15 litre storage water heater. ...
- Crompton Amica 15-L 5-star rated storage water heater. ...
- Crompton Arno Neo 15L Storage Water Heater. ...
- AO Smith SDS-GREEN SERIES-015 Storage 15 Litre Vertical Water Heater.
Overall, if you want to get a water heater that's competitively priced and features modern functionality, Rheem may be the right choice for you. On the other hand, if you're looking for a water heater that's powerful, highly efficient, and long-lasting, you may be better off choosing Bradford White.
What is the most popular type of water heater today? ›Conventional Storage Water Heaters: You've probably seen a single-family storage water heater before. In fact, they are the most popular home water heating systems. Holding between 20 and 80 gallons, they release hot water from the top of the tank and replace it with cold water at the bottom.
How do I know if my tank is too hot? ›The first sign of stress to your fish during hot weather is rapid gill movement or gasping for air at the surface. Corals and anemones will close up and their polyps or tentacles will retract. Algae growth may increase, and the water may begin to turn cloudy due to a bloom of heterotrophic bacteria.
Where is the best place to put an aquarium heater? ›In your home aquarium, the best location for placing a heater is near the maximum water flow, such as the outlet (or inlet) from the filter, or in the stream of a powerhead. Having water flowing directly past the heater is what quickly and evenly disperses heated water throughout the tank.
Is a higher watt heater better? ›High wattage means more power is consumed. Because of this most of the time we are trying to build and use appliances that use less power and have lower wattages. Higher wattages however are good when you particularly need to turn electricity into heat. The higher the wattage the hotter the heater.
How many watts does a 100 gallon water heater use? ›
...
Water Heater Wattage Chart.
| Water Heater Size: | Wattage: |
|---|---|
| 90 Gallon Water Heater | 4500 Watts Or More |
| 100 Gallon Water Heater | 4500 Watts Or More |
The wattage needed will depend on how many degrees you need to increase above room temperature (68-72 degrees fahrenheit). For increasing a 75 gallon aquarium 5-10 degrees fahrenheit, choose the 200 watt heater. If increasing the 75 gallon aquarium by 15 degrees fahrenheit, choose the 300 watt heate...more.
How long will a 30000 BTU heater run on a 100 lb propane tank? ›...
1st Calculation: How Long Will 100-Gallon Propane Tank Last (Based On Heating Need)
| Heating Need (BTU/h): | 100-Gallon Tank Lasts For: |
|---|---|
| 20,000 BTU/h | 15 days |
| 30,000 BTU/h | 10 days |
| 40,000 BTU/h | 8 days |
| 50,000 BTU/h | 6 days |
- Multiply the length times the width times the height to calculate the volume in cubic feet.
- Multiply the room's cubic footage by 4 if its walls contain fewer than 3 inches of insulation.
Here's the catch: Modern water heaters are well-insulated meaning there is very little heat loss. Although electrical rates vary, the experts say turning off the water heater at night will likely save about two dollars a month.
How much does it cost to run a 1500 watt heater for 8 hours? ›For example, running a 1,500-watt heater for 8 hours a day can cost an average of $1.92 each day. That means it will cost many users just under $60 to operate the space heater for 8 hours every day for an entire month.
Is it OK to use 2 heaters in large aquariums? ›In large aquariums, it may require two heaters. For example, a 100 gallon aquarium would require 500 Watts of heat, but it would be better to use a 300 Watt heater at each end of the tank, rather than one 500 Watt heater, to keep the water temperature consistent throughout the aquarium.
How many gallons will a 200 watt aquarium heater heat? ›Our Cascade Aquarium Heaters are factory set to 76 ℉, and are safe for either freshwater or saltwater fish tanks. The 200W model works great for 30 – 55 gallon tanks.
How long will a 5 gallon propane tank run a heater? ›A standard 5 gallon tank holds roughly 4.7 gallons. So a full tank would hold 427,000 BTUs. Therefore, a 40,000 BTU propane heater, such as SunGlo or Patio Comfort on high can get 10 hours and 40 minutes out of a tank.
How many gallons of propane are in a 100 lb tank? ›100lb Propane Tanks: A 100lb pound tank is approximately 4-foot tall and 1.5-foot in diameter. These types of residential propane tanks will hold a little less than 25 gallons of propane when full and can be used for things such as home fireplaces, dryers and grills.
How long will a propane tank last with a 15000 BTU heater? ›
The ProCom Heating Single Infra-Red Tank Top Propane Heater (Single Burner) operates in 3 heat settings with a maximum of 15,000 BTU. These low cost outdoor heaters are the perfect solution when you need instant heat. This small but powerful heater can run for up to 43 hours on a single 20 lb. propane tank.
How do I choose a heater? ›- Heating Capacity. When looking for a space heater, one of the most important things to consider is the amount of space you need to heat. ...
- Heater Type. The next thing to consider is what type of heater you need. ...
- Energy-Efficiency. ...
- Safety Features. ...
- Noise Level.
Larger heaters cover more area and are more effective (while smaller heaters in big spaces are inefficient), but also cost more to run. The second thing that you'll want to consider is energy efficiency.
Does the size of a heater matter? ›Size Does Not Matter
Most space heaters are rated by the size of room they are meant to heat. Oil heaters heat large areas and heat them slowly. They have no fans, typically, and once they come to temperature use relatively little energy; electricity heats the oil, which heats the air.