Grow Room too Cold? Here Are 7 Hacks & 6 Products That Actually Work!

Cold temperature kills plants. Specially indoor grow plants where ‘Mother Nature’ isn’t there to take care of them. And you as a smart grower must be acknowledged of it.

So, what are the threats when your grow room is too cold? To be precise, such critical fall in temperature may cause damage to leaves and roots that leads to less germination and eventually less yield.

None of us growers want that, right?

To deal with the problem, you might have already bought heaters or made a few changes to the growing system. But still, it’s too cold while the lights are off. Specially if your tent is located in a poorly isolated room.

However, we’ve been concerned about this very problem for quite a long and written a guide that’s going to bring the smile back for every grower. Take a moment and pat your back, as this article has got your attention. Get yourself a cup of coffee, take a breath and let’s start gliding through the whole post-

How Cold is ‘Too Cold’ for A Grow Space?

Grow tent temperature never stays the same throughout the day. It’s more likely to have a cycling temperature rise and fall during day and night. For both warm season crops and cool season crops, there are different expectations of this temperature limit.

For Warm Season Crops, it’s good to have a daytime high of mid 70 degrees, and nighttime temperature should be no lower than 60 degrees. For Cool Seasoned Crops, the limits of daytime and nighttime should be set on 60 and 50 degrees respectively.

Now, come to the point of how to keep an eye on the temperature of it. As opening the tent to check the temperature would chill the plants, use something that monitors it for you remotely.

A good idea is to use a Min-Max Thermometer. It calculates the maximum inlet/outlet temperature for past 24 hours and displays that off. An upgrade to that would be a Remote Outdoor Thermometer, which does the same job just with a wireless connection.

Our Recommendations

Min-Max Thermometer: Grower’s Edge Large Display Thermometer

Remote Thermometer: AcuRite 00611A3

Grow Room Too Cold Symptoms

Placing a thermometer and acknowledging the best comfortable temperature range is the best way to identify a ‘too cold’ grow space. Apart from that, check for these following symptoms as well-

  • Small and Weak Growth.
  • Damp areas and unwanted mould.
  • Chilled out root systems(Hydroponics).
  • Bad taste, smell, color or density of grow plants.

Problems that A Cold Grow Room Suffers From

Among the plethora of issues that a ‘too cold’ grow room can suffer from, here are three of the most critical ones-

Low Germination

Most grow plants germinates well in between a temperature of 65-75 degrees Fahrenheit. Some warm-season flowers and vegetables like this range to be 80+ degrees. But with a grow tent cooler than 60 degrees, you can’t expect the plants to even start the process of germination. Eventually, leading to low and poor yield.

Higher Oxygen Concentration

Below-temperature of your grow space will chill the water, leading to a higher concentration of oxygen dissolved in it. While plants intake that through roots, it hinders the metabolism and enzymic processes of plants.

A Damp And Unhealthy Grow System

Low temperature may cause a few cold or hot spots popping up in some places of the entire space. That eventually creates a damp environment and unwanted mould. Both of the issues may leave your plants with severe damage and over-purpling leaves.

7 Actionable Hacks to Deal Wih A Cold Grow Space

Now let’s look at the brighter part of the article. From right here, we’ll be talking about some hacks and solutions to raise the temperature to an expected level.

But before you decide to spend any bucks to solve the low-temp issue, consider these few hacks that might lead a way out of it-

Insulate As Much As Possible

You’re already dealing with a cold temperature inside your grow room. So, you never want the heat fly away before it reaches the plants and nutrients. And the best possible way to make it happen is to Insulate the space as much as possible.

Now, insulating a grow space doesn’t only mean to duct the airflows. Here is a complete list of insulation works you need to do-

  • If you’re growing in pots, wrap Aluminium Foil Sheets around them.
  • If the pots are in direct contact with the cold floor, put a Polystyrene Plastic Sheet in between.
  • Wrap the whole grow tent from outside, leaving no way out for the heat to fly away.

Keep Lights on Instead of Plugging In A Heater

Let’s say your plants are in vegetative development, or not sensitive to photoperiods. In both cases, you don’t really have to keep a heater plugged in to deal with the cold snap. Instead, it’s better to use as many grow lights as possible.

Now, you may raise an eyebrow on running grow lights for 24 hours a day. But the truth is, that will cost less electricity than even 5-6 hours of heater runtime. Moreover, some power supplier companies provide cheaper electricity during the night time.

Improve Air Circulation

You’re about to do something to generate more heat inside the grow space. But what if the heat doesn’t reach the plants and ends up creating hotspots instead?

Make sure to circulate the heat around the entire space. Some heaters come up with circulation method of their own, like a fan. But for many of them, you have to circulate them internally. The best way is to use a standby fan.

Take The Air Intake from A Warmer Space

One of the reasons for a low temperature is lack of warm intake air. And that’s because the intake air is imported from a place that’s not so warmer then grow space itself. Trying to solve the issue may raise the minimum temperature of your grow room.

Putting the Exhaust Fan into Timer

For sake of proper ventilation, you must keep a couple of intake and extraction fan turned on. Usually, that’s no problem as you have internal heating sources like grow lights and heaters. But what if the lights are turned off? Should the extractor fan be switched off to trap the heat inside?

No. But you must try to minify the fan speed. Connecting the extractor fan with a Day/Night Fan Speed Controller is the best choice here. Once you set the temperature limits of day and night, they’ll control the speed automatically based on whether the lights are on or off.

Our Recommendations: Total Controls Zephyr 1

Enhance The Nutrient’s Heater by 20%

You might be suffering from not only a chilled up grow space, but also chilled up nutrient solutions. The damage that a cold nutrient solution can cause to your plant is severe.

As a solution, you may try increasing the nutrient strength by 20%(or so), so that the plants may intake the necessary nutrients without as less water as possible. Eventual, the effects of low temperature on the plant’s health will be minified a lot.

Warning: Remember, plants transpire less in a chilled condition. So commercial growers may have to compensate for increasing the nutrient strength.

Turn Composts Into Heat Sources

It may sound weird, but we’re pointing to a method that warms up the composts and turn them into heat sinks. As your tent is likely to chill at night time, storing some heat inside the compost piles is a great idea.

The process is simple. Create a trench in a place which is warm during the daytime. Let the daylight heat up the compost piles and they will release the heat later in the night. Just chose the place of heating composts carefully.

6 Best Heat Sources for Your Grow Space

Thermostat Controlled Electric Grow Heaters

The most familiar, and possibly the most effective of your problem, in case if you’ve not got one yet. In a broad sense, we can split up all electric heaters based on the size of grow space-

1) Electric heaters for Grow Room.
2) Electric heaters for Grow Tent.

Here are the differences-

  • Size & Heating Power
    Where heaters for grow rooms are larger in size and weight, heaters for tents are lighter and smaller. The power(in terms of Watt) lies within 1500-2000W for room heaters and 750-1500W for tent heaters.
  • Runtime
    You may need to run the heater for specific hours in a day, mostly based on the light cycle. For an 18/6 or 16/8 light cycle, smaller heaters will do good with the 8 hours of continuous runtime. The larger ones are more fit for grow rooms, where you may need to run it for even 24 hours.
  • Oil Filled Vs Ceramic
    This is another important difference that may influence your buying decision. A simple explanation of oil-filled Vs ceramic heater is- it’s the heat creation medium that matters. In case of an oil filled one, the fins are filled up with heated up oils, generating radiant heat. And in the case of ceramic heaters, ceramic is the heating material that generated radiant convention heat.

In case you’ve not got one, it’s the first and foremost recommendation to deal with your heating problem. However, keep the price, energy expense and positioning in mind, while purchasing one for your grow space. You can check out our buying guide on best grow room heaters.

Our Recommendations

Best grow room heater with thermostat: DeLonghi EW7707CM 1500W Radiant Heater

Best grow tent heater with thermostat: Vornado MVH Whole Room Vortex Heater

Grow Tent Tube Heaters

A tubular heater is the most effective and simplest heating solution off all the available options in the market. It consumes only a few watts of power(90- 200W) and is a great fit for growing spaces with small foot space.

Best tube heaters in the market come with a number of beneficial features like- A safety cut out, Overheating prevention, added on adjustable legs etc. For larger space, more than such heaters may be needed.

However, the best place to put a tube heater is on the floor instead of on the grow tray. In that case, you need to raise the tray level a little bit by putting some empty pots as support. Anyways, make sure that there is enough air flow to spread the heat around the base. This will heat up the substrate and root system that encourage healthier yield.

For best results, you may use a temperature controlled programmable extractor fan that will work based on the temperature.

Our Recommendations

Tube Heater: Star HE-197829 Heater Tube

Heating/Cooling Mini Splits

If you’re living in a continental climate zone, you know it’s too cold in winter and too hot in summer. You’re facing a temperature fall right now and will suffer from a too hot problem in summer. Eventually, you’ve to spend after both cooling and heating solutions.

Why don’t we combine both of them together? I’m talking about a Heating/Cooling Mini Split that you already know. It contains one indoor and one outdoor unit and offers a wide variety of BTU. Typically, a good heating/cooling mini-split can offer a wide range of both heating and cooling.

You might be worrying about the price and energy cost. Sadly, these units are expensive enough. But if you be a smart buyer, your model might give you a 30-50% energy savings.

Our Recommendations: Ideal-Air Pro Series Mini Split(36,000 BTU)

Soil Mats

Whenever there is an issue like chilled grow space, Most of us growers focus on heating the air inside it. But one of the first things to do is to try heating the soil/seeding instead.

These mats work with a mission to keep the soil temperature in between ideal ranges, mostly 75-85°F. Practically, which is way more expensive to acquire by heating the air.

Some people always only these mats as germination mats. Don’t be fooled by that, because these mats are great to heat soils even after the germination stage.

Our Recommendations: Soyon 300W Aquarium Heater

A Cheaper Alternative: U-picks 30W Aquarium Heater+Thermometer

Aquarium Heater: To Warm Up The Nutrients

Cold roots are one of the greatest threats for any grower, especially who grows in a media-less system. What I mean by media fewer systems are- NFT(), DWX(), Aerophonics etc.

Reason? Well, these kinds of plants lack the insulation that growing media like soil can provide.

The solution is simple- heat up the nutrient solution externally. An extraordinary tool to do that is Aquarium heater. One such heater can surely raise the temperature to 70+ degrees Fahrenheit.

Our Recommendations

Water Storage

Just a while ago, we talked about turning soil composts into heat storing composts piles, and it works great. This time, we’re talking about implementing the same idea with a barrel of water.

To build up this heatsink, use a 55-gallon barrel, or any handy water storage you prefer. Place the container in an area where the sunlight can heat it. Later on, place it inside the grow room and let the water release heat energy. In this way, a well-sized water barrel will fight against cold temperature for quite some hours.

For better result, use a dark tank for maximum heat absorption.

Our Recommendations: RTS 50-Gallon Rain Water Collector Barrel

Frequently Asked Questions(FAQ)

Question: What’s the best time for heating?
Answer: It depends on the temperature outside of the growing tent, and how much heat is demanded plants. Usually, it should be after evening, when it’s starting to cool down. However, in winter, heating quite often is an evil necessity.

Question: How to keep grow room warm when lights are off?
Answer: Use something like an automatic fan speed controller that works on whether the light of your grow room is on or off. While it’s night, it will automatically deduce the fan speeds, resulting in a gradual increment in temperature.

Question: What is the cheapest way to heat a grow room?
Answer: If you’re not interested to buy a whole unit of an electric heater, some cheaper options to get a water storage, soil mat or aquarium heater. Providing intake air from a warmer space is maybe the most cost-effective idea.


I'm Saleh, a hobbyist DIYer, and a blogger. is my little place on the web to express what I've learned first-hand, specially about home improvement.

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