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The running costs of a desiccant dehumidifier car storage system

There are seemingly solutions aplenty for storing a car and tackling the effects of uncontrolled humidity. Here we will look at four standard ‘solutions’ and compare them to car dehumidifier running costs.

car dehumidifier running costs

Car Dehumidifier Running Costs versus Alternative methods

Two of these do offer a solution, but at what cost?  The other two do not to provide an effective solution, as a specialist engineering company we do get asked if they are a viable solution, worth consideration, therefore we have included them for comparison. 

Our primary focus for this study will be on:

  • Heating
  • Domestic Dehumidifier
  • Ventilation
  • Car Covers

We will see these 4 ‘solutions’ stack up against Protects engineering dry air solution. We have conducted a test based on a 4 car garage in the UK, which has an average RH externally of 80% and an average temperature of 14oC. The charts below show a summary of the conclusions drawn from the study.  Beyond the charts is a full explanation of how these conclusions have been drawn.

The Base Environment

There are many variables in a calculation such as this, we will take the average weather conditions in the UK, and these are 14oC and 80%RH, which is a moisture content of 7.98g/kg.  We have used an average four-car garage measuring 6m x 12m with standard brick construction and a tiled roof.

Utilising design calculating tools from CIBSE and ASHRAE, we can create a standard environment in which we can base conditions for comparison.

Solution’s Design Goals

The design of each method must be to maintain the optimal conditions for a vehicle of 40%RH within the garage. Buildings naturally incur energy losses, and we will use the two most common:

  • Air Infiltration (AI) (natural leaking of the building through gaps and cracks.)
  • AI using standard CIBSE guides the air infiltration rate for a building of this size would be 0.5ACH, equating to 133.2m3/h.
  • Heat transmission (HT) through building materials, heat loss based on the U value (the insulation rating given to building materials)
  • HT would use 2w/m2K for the walls, 6.8w/m2K for the garage door and 2.8w/m2K for the roof.

Now that we have established the building size’s base numbers and the associated energy losses, we can compare.

Protect Engineered Solution – AD300

With dehumidification, you are dealing with the problem at the source; high humidity is too much moisture in the air, causing corrosion on the vehicle.

Our unique Dehum technology uses a desiccant rotor, which is unaffected by temperature and can remove moisture at any condition, even down at -40oC.

The equipment focuses on what’s important, the protection of your car; with no requirement to heat the building, we remove the water from the air at any temperature.

The humidity control using a desiccant unit is done through absorption; as the air passes through the desiccant rotor, the moisture is absorbed into the rotor and then vented to the atmosphere. As the humidity is controlled in this way, you will only ever use the required energy to remove the moisture from the air.

The unit required to hold the garage at 40%RH year-round is the AD300, and this has an installed power requirement of just 1.51kw. Controlled by a central control unit, the equipment will only ever use the energy required to protect your car. As you will see, this is significantly lower than other options on the market.


We have seen attempting to heat a building to increase the air’s capacity to hold moisture, which will reduce the RH within the air and the garage. To take air at 14oC and 80%RH, we would have to heat the internals of the garage to 25oC. 

Based on the energy requirements to compensate for the losses noted above and to heat the building to 25oC, this would need 6.037kw of heat required per hour.

Domestic Dehumidifier

Most domestic dehumidifiers are refrigerated, which relies on their ability to cool and condense moisture from the air using a cold surface. The limitation of refrigeration in this application is the lowest temperature the refrigeration coil can achieve, about 6oC.

Due to this fact, to maintain 40%RH within the garage using refrigeration, you would also need to heat the space simultaneously. Based on this the heat loss and energy requirements to heat the building when its 14oC outside and you need 20oC Inside would be: 3.293kw of heat required per hour

To maintain 40%RH in the garage, the area itself would have to be kept above 20oC year-round with the addition of refrigeration, so not only are you trying to remove the moisture but you are also required to heat the space.

The heat loss and energy requirements to heat the building when it’s 14oC outside and you need 20oC Inside would be: 3.293kw of heat required per hour. The refrigeration unit required to remove 0.314kg/h of water from the air held at 20oC and 40%RH would require 1.58kw of cooling capacity. The total energy required to maintain the space at 40%RH would be 4.877kw.


We commonly hear car owners are using Ventilation to combat the effects of RH because it doesn’t cost anything. But while Ventilation may help dry your car more efficiently, if you’ve put it away wet, bringing in air from the outside only introduces the moisture in that air into your environment. With the UK’s average RH being so high, Ventilation is not a practical solution. From this, we would deduce that your ongoing running costs and upkeep cost would be the same as if you had no solution in place at all.

Car Covers

Covers are an excellent option for keeping dust and dirt off your car, as well as protecting the paintwork from UV rays while it’s sitting outside, but that’s far as it goes. In terms of dealing with relative humidity and protecting your car, it’s completely ineffective- in fact, a car cover could do more damage if the moisture condenses on it, leading to rusting and paint damage on the car.

You will be leaving yourself exposed to avoidable ongoing upkeep costs. In fairness, your total ongoing costs are relative to the number of cars you own and their value, but we can surmise that using just a car cover alone, you’re continuing costs to protect them can be valued at Infinite.