High humidity in the house during summer? An enthalpy exchanger can help
High Humidity in the House During Summer? An Enthalpy Exchanger Could Be the Solution
In summer, many heat recovery unit owners deal with high humidity inside their homes. As a result, they often ask whether it makes sense to use an enthalpy exchanger during the summer or if they should replace it with a standard one.
In most cases, the answer is clear: an enthalpy exchanger makes perfect sense in the summer. If the outdoor air is warm and humid while the house is cooled inside, the enthalpy exchanger helps limit the amount of moisture brought into the interior through ventilation.
A standard heat exchanger transfers cold from the exhaust air in summer, but it barely reduces the humidity of the incoming outdoor air. As a result, the air entering the house is cooled but remains humid.
An enthalpy exchanger, on the other hand, transfers not only cold but also a portion of the water vapor. Thanks to this, it can supply the house with cooled air at a lower humidity level.
Why Does High Indoor Humidity Occur Specifically in Summer?
In summer, outdoor air is often not only hot but also highly humid. When a ventilation unit brings this air into the house, it also brings a significant amount of water vapor with it.
This problem is particularly pronounced in modern cooled homes, where the indoor temperature is lower than outdoors. When the air cools down, its relative humidity rises, making the indoor air feel heavy, stuffy, and uncomfortable.
| Humid outdoor air | brings water vapor into the house even during normal ventilation |
| Cooled interior | lowers the air temperature, causing the relative humidity to rise further |
| Higher perceived temperature | humid air feels stuffy and degrades thermal comfort |
Standard Exchanger vs. Enthalpy Exchanger in Summer
The fundamental difference is not in the temperature of the supplied air, but in its humidity.
| Standard exchanger | Enthalpy exchanger |
| transfers cold from the exhaust air | transfers cold from the exhaust air |
| barely reduces the humidity of the supplied air | also transfers a portion of the water vapor |
| Cooled but still humid air enters the house. | Cooled air with lower humidity enters the house. |
A standard exchanger primarily helps with temperature. An enthalpy exchanger helps with both temperature and limiting the moisture brought in from the outside.
Graphical Representation of the Exchanger Principle in Summer
Below is a direct comparison between a standard non-enthalpy exchanger and an enthalpy exchanger in summer operation.
A standard exchanger supplies the house with cooled but humid air. An enthalpy exchanger supplies cooled air with lower humidity.
We Measured It Using Specific Data
For a clear comparison, we used calculations for two similarly sized heat exchangers from the manufacturer RECUTECH:
| RECUTECH RSK+16-500-25 | standard non-enthalpy exchanger |
| RECUTECH RFK+16-500-28 | enthalpy exchanger |
Therefore, this is not just a general claim, but a direct comparison of two real exchangers under the exact same inlet conditions.
Model Inlet Conditions
The comparison is based on a summer scenario where the outdoor air is hot and humid, and the house is cooled inside.
| Condition | Outdoor fresh air | Exhaust air from the house |
| Temperature | 35 °C | 25 °C |
| Relative humidity | 50 % RH | 60 % RH |
| Absolute humidity | 17.8 g/kg | 11.9 g/kg |
| Airflow rate in the calculation | 50 m³/h | |
Result at the Supply Inlet to the House
Both exchangers cool the incoming outdoor air to a similar temperature. The difference, however, lies in the humidity.
| Supply air parameter | RSK+16-500-25 standard exchanger |
RFK+16-500-28 enthalpy exchanger |
| Supply air temperature | 25.5 °C | 25.5 °C |
| Supply air relative humidity | 86.0 % RH | 71.2 % RH |
| Supply air absolute humidity | 17.75 g/kg | 14.60 g/kg |
| Difference compared to standard exchanger | 0 g/kg | -3.15 g/kg |
In this calculation, the enthalpy exchanger reduces the absolute humidity of the supplied air from 17.75 g/kg to 14.60 g/kg. Consequently, air entering the house is at the same temperature but with a significantly lower humidity level.
What Does a Difference of 3.15 g/kg Mean in Practice?
At first glance, a value of 3.15 g/kg might seem small. However, a ventilation unit operates many hours a day and introduces tens to hundreds of cubic meters of air every hour.
In total, this represents a significant amount of water that would otherwise enter the house if a standard exchanger were used.
| Operating Scenario | Approximate amount of water kept out of the house |
| At a flow rate of 50 m³/h | approx. 0.18 l/h |
| At a flow rate of 200 m³/h | approx. 17 l/day |
Practical Significance:
On a model summer day, at a standard airflow rate, an enthalpy exchanger can significantly limit the amount of water that would enter the home solely due to ventilation.
How Does an Enthalpy Exchanger Transfer Moisture?
An enthalpy exchanger features a special membrane that allows a portion of water vapor to be transferred between the two air streams. The direction of moisture transfer is not fixed. It depends on the current outdoor and indoor conditions of the house.
| In winter | the outdoor air is cold and dry, while the indoor air is warmer and more humid – the enthalpy exchanger helps return a portion of the moisture back into the house |
| In summer | the outdoor air is often warm and humid, while the house is cooled inside – the enthalpy exchanger helps transfer a portion of the moisture into the exhaust air |
This makes the enthalpy exchanger a year-round solution. In winter, it helps prevent overly dry air, while in summer, it protects against excessive moisture intake from the outside.
When Does an Enthalpy Exchanger Help the Most in Summer?
| Cooled homes | air conditioning, fan coils, or radiant ceiling cooling experience a reduced moisture load |
| Modern insulated homes | lower moisture intake helps stabilize the indoor climate |
| Passive and low-energy houses | controlled ventilation operates continuously, so the difference in humidity accumulates over time |
| Regions with sultry summers | the benefits of an enthalpy exchanger are most noticeable when outdoor humidity is high |
Main Advantages of an Enthalpy Exchanger in Summer
| Less outdoor moisture | limits the amount of water vapor brought into the house by ventilation |
| Reduced cooling load | the cooling system does not have to deal with such a high moisture load afterward |
| Greater comfort | the air feels more pleasant and less stuffy |
| Year-round utilization | it helps retain moisture in winter and limits its intake in summer |
| Suitable for modern homes | ideal for houses with heat recovery, cooling, fan coils, or radiant ceiling cooling |
Important Notice
An enthalpy exchanger is not a refrigerant dehumidifier or an air conditioning system with active dehumidification.
If a house suffers from long-term very high humidity—for instance, due to a new build, wet structures, construction moisture, indoor clothes drying, or another strong source of moisture—the enthalpy exchanger alone will not instantly solve the problem.
Its primary benefit lies in limiting the influx of new outdoor moisture during ventilation. By doing so, it helps stabilize the indoor climate and reduces the building's moisture load.
Myth vs. Reality
| Myth | Reality |
| An enthalpy exchanger increases indoor humidity in summer. | In typical summer operation with a cooled interior, it actually restricts the intake of outdoor moisture. |
| A standard exchanger is always better in summer. | A standard exchanger transfers cold, but it still allows outdoor air humidity into the home. |
| Enthalpy exchangers only work in winter. | It works year-round. It combats dry air in winter and high moisture loads in summer. |
| I don't need an enthalpy exchanger if I have cooling. | It makes a lot of sense precisely when cooling, as it lowers the amount of moisture brought in by ventilation. |
Choose the Right Enthalpy Exchanger for Your Unit
Would you also like to lower the humidity of supplied air during the summer months?
On our e-shop, you will find a wide range of compatible enthalpy exchangers for many types of heat recovery units from various manufacturers.
➡ View the selection of enthalpy exchangers by heat recovery unit manufacturer
Can't find your unit on the list?
Drop us a line at info@rekupex.cz. In most cases, we can recommend a compatible enthalpy exchanger or propose a suitable solution even for less common heat recovery units.
Frequently Asked Questions
Does an enthalpy exchanger make sense in summer too?
Yes. If the outdoor air is warm and humid while the house is cooled inside, the enthalpy exchanger helps reduce the humidity of the supplied air.
Does an enthalpy exchanger increase indoor humidity in summer?
Not in a typical summer scenario with a cooled interior. In fact, it does the exact opposite by restricting the intake of outdoor moisture.
Does this mean there will automatically be ideal humidity at home?
Not automatically. The resulting humidity depends on outdoor conditions, ventilation, cooling, and internal sources of moisture. However, the enthalpy exchanger limits the influx of new moisture from the outside.
Should I swap my enthalpy exchanger for a standard one in summer?
In most cases, no. If you are dealing with high indoor humidity, an enthalpy exchanger is highly beneficial for summer operation.
Will an enthalpy exchanger help if I use fan coils or radiant ceiling cooling?
Yes. It reduces the moisture load carried by the supplied air, which is crucial for cooled homes.
Does an enthalpy exchanger replace a dehumidifier?
No. An enthalpy exchanger is not an active dehumidifier. However, it significantly minimizes the amount of moisture that enters the home through ventilation.
Summary
A standard exchanger transfers cold in summer, but it does not transfer moisture. As a result, the outdoor air entering the house is cooled but remains humid.
An enthalpy exchanger transfers both cold and a portion of the water vapor. Thanks to this, cooled air with lower humidity enters the house.
In the model calculation, the absolute humidity of the supplied air dropped from 17.75 g/kg to 14.60 g/kg. At a standard airflow rate, this difference can amount to roughly 17 liters of water per day that never make it inside the house.
Therefore, an enthalpy exchanger is a year-round solution: it helps combat dry air in winter and shields against excessive outdoor moisture in summer.
Article Author
Vojtěch Špulák
Heat recovery exchanger specialist and founder of RekupeX.
RekupeX specializes in compatible heat recovery and enthalpy exchangers for hundreds of types of ventilation units. We manufacture and supply solutions for residential and industrial ventilation across Europe.
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