What Is A Humidistat And Do I Need One?
Learn what a greenhouse humidistat does, how it controls humidity, when you need one and how to manage excessive or low humidity in a greenhouse.
If you grow plants in a greenhouse, you may already use a thermometer or thermostat to monitor temperature, but humidity can be just as important. A humidistat is a device designed to measure relative humidity and automatically control compatible equipment when humidity reaches a selected level.
Unlike a thermostat, which responds to temperature, a humidistat responds to moisture in the air. This makes it useful where you need more consistent control of greenhouse humidity and have suitable equipment, such as a humidifier, dehumidifier or compatible fan, that can change the conditions inside the growing space.
The Elixir Gardens TH-928H Plug-In Digital Humidistat is designed for this type of automatic control. It displays humidity from 10–99% RH and provides humidity-based control from 20–90% RH, allowing compatible equipment to respond automatically as conditions change.
However, owning a greenhouse does not automatically mean you need a humidistat. Many gardeners can manage greenhouse humidity effectively through ventilation, sensible watering, plant spacing and regular monitoring. The important question is whether you have a genuine humidity-management problem that would benefit from automatic control.
Quick Answer
A humidistat measures relative humidity (RH) and can automatically control compatible equipment according to a selected humidity level.
It is different from a thermostat, which measures and controls temperature. It is also different from a hygrometer, which measures humidity but does not normally control other equipment.
The Elixir Gardens TH-928H Digital Humidistat has a published display range of 10–99% RH and a control range of 20–90% RH, with humidity accuracy specified at ±5% RH. It can be used with compatible humidifiers, dehumidifiers, fans and other suitable equipment.
For many ordinary garden greenhouses, basic ventilation and sensible watering may be enough. A humidistat becomes more useful when humidity needs to be controlled automatically or when changing humidity manually is difficult.
What Is Humidity?
Humidity describes the amount of water vapour present in the air. In greenhouse growing, this is generally discussed as relative humidity, expressed as a percentage or RH.
Relative humidity is affected by temperature because warmer air can hold more water vapour than cooler air. This is why a greenhouse can show significant changes in RH between the daytime and night-time even when no additional water has been introduced.
For gardeners, humidity matters because plants are constantly interacting with the moisture in the surrounding air. It affects transpiration, water loss, drying rates, condensation and the growing environment around leaves and roots.
The aim is not necessarily to make a greenhouse as humid as possible. Different plants have different requirements, and excessive humidity can become problematic when combined with cool temperatures, poor ventilation and stagnant air.
Why Does Humidity Matter In A Greenhouse?
Greenhouses naturally create an environment where moisture can build up. Plants release water vapour through transpiration, while watering, damp compost, wet surfaces and condensation can all contribute additional moisture.
During warm periods, some plants may benefit from higher humidity because it can reduce the rate at which they lose water. However, persistently damp conditions can create a less suitable growing environment, particularly when there is little air movement.
This is why ventilation remains one of the most important tools for managing greenhouse humidity. Opening suitable vents allows moist air to escape and brings in outside air, helping reduce excessive humidity and condensation when conditions allow.
Before buying automatic humidity equipment, look at the basic causes first. Improve ventilation, review watering, increase plant spacing where necessary and remove dead plant material. If humidity remains difficult to manage, automatic control may then be worth considering.
What Is A Humidistat?
A humidistat is essentially the humidity equivalent of a thermostat. Instead of measuring temperature and switching equipment according to temperature, it measures relative humidity and switches compatible equipment according to humidity.
The humidistat itself does not normally remove or add moisture. Instead, it acts as the controller between the humidity level and the appliance being used to change it.
For example, a suitable dehumidifier can remove moisture from the greenhouse, while a compatible humidifier can increase humidity. A suitable fan may also be controlled where the arrangement is appropriate for reducing excessive humidity.
The benefit is that the equipment does not necessarily have to be switched manually every time conditions change. Once the humidistat is correctly configured, it can respond automatically to the measured RH.
What Is The Elixir Gardens TH-928H Digital Humidistat?
The Elixir Gardens TH-928H Plug-In Digital Humidistat is designed to provide automatic humidity-based control for compatible equipment. Rather than simply displaying the humidity, it can switch suitable connected equipment according to the selected humidity setting.
Elixir specifies a humidity display range of 10–99% RH and a controllable range of 20–90% RH. The published humidity accuracy is ±5% RH, while the unit has a specified switching capacity of 3120W / 13A and a temperature range of 15–40°C.
This makes the TH-928H particularly relevant to gardeners who already have suitable equipment and want that equipment to respond automatically when greenhouse humidity changes.| Specification | TH-928H |
|---|---|
| Humidity display range | 10–99% RH |
| Humidity control range | 20–90% RH |
| Humidity accuracy | ±5% RH |
| Temperature range | 15–40°C |
| Output voltage | 230V / 50Hz |
| Switching capacity | 3120W / 13A |
| Approximate dimensions | 140 Ă— 70 Ă— 41.5mm |
Do I Need A Humidistat In My Greenhouse?
Not necessarily. For many home gardeners, humidity can be managed effectively without electronic control.
Good ventilation, appropriate watering, sensible plant spacing and regular monitoring should generally be the starting point. If your greenhouse is well ventilated and your plants are growing normally without persistent condensation or humidity problems, there may be little reason to add an automatic humidistat.
A humidistat becomes more useful when the greenhouse environment needs closer control. This might be because you regularly experience excessive humidity, operate compatible humidity control equipment, grow plants with more specific environmental requirements or cannot monitor the greenhouse regularly throughout the day.
The TH-928H Digital Humidistat is therefore best viewed as a control solution rather than an essential greenhouse accessory. It becomes valuable when there is equipment available for it to control and a genuine need for automatic humidity management.
When Is A Humidistat Worth Having?
A humidistat can be useful when humidity repeatedly moves outside the conditions you are trying to maintain and manual management is becoming inconvenient.
For example, you may have a greenhouse where condensation regularly forms overnight, or you may be operating a compatible dehumidifier and want it to switch on automatically when RH reaches a selected level.
It can also be useful in more controlled growing environments where humidity forms part of the overall growing strategy. In these situations, the TH-928H provides a way of linking humidity measurements with compatible equipment rather than relying on visual observation alone.
The important point is to identify the actual problem first. If better ventilation or improved watering would solve the issue, those changes should not be replaced simply by installing a humidistat.
When Do You Probably Not Need One?
You may not need a humidistat if your greenhouse is naturally well ventilated, humidity problems are uncommon and you can manage the environment manually.
There is also little benefit in buying a humidistat if you only want to know the humidity. In that situation, a suitable hygrometer or humidity meter is the more relevant type of device because it provides the measurement without the additional control function.
Likewise, if the main problem inside your greenhouse is temperature rather than humidity, a humidistat is not the appropriate solution. Temperature should be managed with suitable heating and a thermostat.
Humidistat And Thermostat Together
A more controlled greenhouse environment may use both a thermostat and a humidistat because they perform separate functions. A thermostat responds to temperature, while a humidistat responds to relative humidity. Using the appropriate controller for each condition allows heating and humidity-management equipment to operate according to the environmental factor they are designed to measure.
For temperature control, the Elixir Gardens Digital Plug-In Thermostat (TH-928T) provides a simple way to automate compatible heating equipment. The thermostat plugs directly into a standard socket, with the heater or other compatible appliance then plugged into the thermostat. Once the required temperature has been selected, the controller can stop and start the connected heater as the temperature rises and falls. Elixir specifies a control range of 5–30°C, making it suitable for a range of greenhouse heating applications.
The TH-928H Digital Humidistat, by comparison, deals with a completely different measurement. It monitors relative humidity and can control compatible equipment according to the selected RH level. This means the two controllers can work alongside each other where both temperature and humidity require automatic management.
This approach can be useful in a more controlled greenhouse, but a basic greenhouse does not automatically need both devices. If your main problem is cold temperatures, start with suitable heating and temperature control. If humidity is the issue, focus on ventilation and moisture management first, then consider a humidistat if automatic control is genuinely required.
What Humidity Should A Greenhouse Be?
There is no single humidity percentage that is correct for every greenhouse.
The appropriate conditions depend on what you are growing, the growth stage, temperature, season, ventilation, propagation method and the susceptibility of the plants to fungal problems.
Rather than choosing a number simply because it is commonly quoted online, consider the requirements of the plants and monitor what is actually happening inside your greenhouse.
Common Humidistat Mistakes
- Confusing a humidistat with a thermostat
- Assuming every greenhouse needs one
- Buying a humidistat without compatible equipment to control
- Assuming the humidistat removes moisture itself
- Chasing one universal humidity percentage
- Ignoring temperature
- Ignoring ventilation
- Overwatering
- Positioning the sensor beside wet compost
- Placing the sensor in direct sunlight
- Placing the sensor beside the controlled appliance
- Confusing air circulation with ventilation
- Ignoring electrical compatibility
- Using humidity control when temperature is the real problem
- Trying to control the whole greenhouse from a poor sensor position
Plug-In Digital Humidistat (TH-928H)
Best For
Automatic humidity-based control of compatible greenhouse equipment.
Why Choose This Product
The TH-928H allows suitable equipment to respond automatically to changing humidity rather than relying entirely on manual monitoring and switching.
Recommended When
You have a genuine requirement for more controlled humidity and suitable equipment capable of changing the humidity inside your greenhouse.
Digital Plug-In Thermostat (TH-928T)
Best For:
Greenhouses, garages, sheds, kennels and other suitable spaces where accurate digital temperature control is required.
Why Choose This Product:
The TH-928T provides digital temperature control from 5°C to 30°C, with a maximum resistive load of 13A / 3120W. It also features a Hot / Cold setting, allowing it to control heating or cooling equipment depending on the temperature requirements of the space.
Recommended When:
Choose the TH-928T when you want precise digital control and automatic temperature management rather than a traditional analogue thermostat. It is particularly useful for maintaining a more consistent temperature in greenhouses and other enclosed areas. Always check the heater’s electrical load and follow the manufacturer’s instructions before use.
Analogue Thermostat with External Wire Probe (TH-926TE)
Best For:
Greenhouses, growing areas and other spaces where you need straightforward temperature control but the thermostat needs to measure temperature away from the plug socket.
Why Choose This Product:
The TH-926TE combines simple analogue controls with a 2m external temperature probe, allowing the sensing point to be positioned where temperature measurement is more useful. It provides a 5°C–30°C control range and can handle up to 13A / 3120W resistive loads.
Recommended When:
Choose the TH-926TE when the thermostat socket is poorly positioned for accurate temperature sensing or when you want to monitor temperature at a specific point within the growing area. It is particularly useful where a remote sensing point provides more practical temperature control than a standard plug-in thermostat.
Summary
A humidistat is best understood as a humidity-based automatic controller. Where a thermostat responds to temperature, a humidistat responds to relative humidity.
The Elixir Gardens TH-928H Plug-In Digital Humidistat provides a published humidity display range of 10–99% RH and humidity control from 20–90% RH. It is designed to control compatible equipment such as suitable humidifiers, dehumidifiers and fans according to the selected humidity setting.
However, not every greenhouse needs automatic humidity control. For many gardeners, ventilation, sensible watering, suitable plant spacing and regular monitoring remain the most practical starting points.
If those measures are not enough, or if you already operate compatible humidity-control equipment and want it to respond automatically, the TH-928H provides a way to introduce more controlled humidity management.
Frequently Asked Questions
What Does A Humidistat Do?
A humidistat measures relative humidity and can switch compatible equipment according to a selected humidity setting.
Is A Humidistat The Same As A Thermostat?
No. A thermostat controls according to temperature, while a humidistat controls according to relative humidity.
Does Every Greenhouse Need A Humidistat?
No. Many home greenhouses can be managed through ventilation, watering, plant spacing and regular monitoring.
What Is Relative Humidity?
Relative humidity describes the amount of water vapour present in the air relative to the amount the air can hold at its current temperature.
What Does RH Mean?
RH means relative humidity.
What Is The TH-928H?
The TH-928H is Elixir Gardens’ plug-in digital humidistat designed for humidity-based automatic control of compatible equipment.
Follow the Instructions
Every gardening product is designed to be used in a specific way. Always read the product label and follow the manufacturer’s instructions before use. Correct preparation, application and timing help ensure the best possible results while promoting safe and responsible use.
Wear Appropriate PPE
Some products may require suitable personal protective equipment (PPE) during handling or application. Depending on the product, this may include gloves, eye protection or protective clothing. Always check the product label to determine the recommended safety precautions before use.
Application Rates
Using more product than recommended will not usually improve performance and may lead to unnecessary waste or undesirable results. Measure accurately, apply evenly and follow the recommended application rates and guidance provided on the product label.
Rhys Nield
As one of our resident product experts, Rhys has spent the last 2 years helping keen gardeners and growers from within our customer services department. Remember to save this page, or visit the Advice Centre, for the latest tips, articles, and expert knowledge, to help you make your garden the best it can be.
Digital Plug-In Thermostat (TH-928T)
£16.58 £136.24Price range: £19.89£16.58 through £163.49£136.24 incl. VATex. VAT
Analogue Plug-In Thermostat (TH-926T)
£14.08 £131.88Price range: £16.89£14.08 through £158.25£131.88 incl. VATex. VAT
Plug-In Digital Humidistat (TH-928H)
£24.91 £218.54Price range: £29.89£24.91 through £262.25£218.54 incl. VATex. VAT
Analogue Plug-In Thermostat with External Wire Probe (TH-926TE)
£19.58 £141.88Price range: £23.49£19.58 through £170.25£141.88 incl. VATex. VAT
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