Condensation control using Warm Air Dehumidification

A new range of fans have been introduced that provide powerful yet low cost condensation control and dehumidification, this is achieved by the use of intake and extract ventilation combined with a heat source.

In this case we have combined an extractor and intake fan and enabled the pair to fit on to a standard 4 inch/100 mm extract duct. By combining the latest fan technology with a solid-state heater block it is possible to simply swap over from your existing extract only fan.

This combination creates a warm air dehumidification fan that would normally be fitted in your bathroom, the operation sequence is as follows, when unoccupied the fan will bring in fresh pre-warmed air from outside this is filtered providing clean fresh slightly warm air into your Bathroom area, when entering the bathroom your presence will be detected and after a short period of time the fan will turn the internal heater off and start air extraction.

The extract air humidity levels are detected and the required extract period is then calculated, the solution will determine how long the extract fan will run on extract.

When you leave the bathroom and the predetermined extract period has completed, the fan will then revert back into supplying fresh air, this pre-warmed air will provide you with a further drying provision for your whole house as this fresh air will filter through into the rest of your home. In practice this will prove to be beneficial in more ways than just condensation control it provides you with a healthy supply of fresh clean air and as this slightly increases the air pressure into your home it will have the effect of reducing unwanted air infiltration in other areas.

In the first instance you will notice a difference in the reduced amount of condensation (good condensation control) and possibly dust, and in addition to this you will feel the benefits of having a warmer dryer bathroom to go in to, it feels comfortable in fact and in reality it will allow you to delay turning on of the whole heating system, simply because the bathroom is the first place you go into when you get up in the morning.

Running cost:

The unit includes a 200 watt heater, this is not on at all times as it will turn off when the external temperature is above 14OC and has an on board temperature sensor that stabilises the power demand depending on ambient temperatures, the running cost can on average be between £1 & 1.50 a week to run depending on internal temperature and insulation of your property. In return you will have a dryer home less damage through condensate, reduced air bourn mould and a more comfortable environment.

For landlords less reason for your tenants to complain!

7 thoughts on “Condensation control using Warm Air Dehumidification

  1. Gilly says:

    Dear Ray,

    I have a question about your warm air dehumidification system. Please forgive me, I know very little about these things and am having to learn as I go as I try to solve chronic damp problems in my period sub-basement flat.

    Having gathered temperature and RH readings over a 14 day period, I know that %RH in the flat ranges from the low 60s to high 80s (when showering/tumble drying/cooking). But we live in a very wet city and the external RH often reaches these same high percentages even on very warm days.

    On a cold humid day, the warm air dehumidification system would extract the humid air from the flat and use its heat recovery to heat the incoming cold air, thereby dropping its RH% and introducing warmed, dry air into the flat.

    However, what happens if you have a warm humid day, where the external temperatures and %RH are similar to the flat? Heat recovery will surely not help to change the %RH of the external incoming air in this instance? So what you would draw into the flat would be external air (albeit filtered) that was just as humid as the internal air. Am I correct in this assumption?

    Is heat recovery (to lower the %RH of cold incoming external air) the only form of dehumidification that the warm air dehumidification system uses? Or is it also fitted with a dehumidifier?


    • Ray says:

      Thank you for your evaluation. You have determined correctly if the external humidity and temperature are the same or higher than the internal then dehumidification will not occur. In answer to your question do our warm air dehumidifiers have a dehumidifier – if your reference to a dehumidifier means something with a cold plate to attract moisture then heat the plate up periodically to drip out the moisture the answer is no. Our units provide a dehumidifier process when the external air is cooler than the internal air that is being displaced.
      Consideration for your sub basement flat
      Sub basement flats are as you are aware from your experience prone to damp issues, the differential factors from a flat above the surface are;
      1. Your flat envelope is sealed to stop water penetration; this also inhibits water evaporating through the structure to external – no ability to breath.
      2. The temperature of the external walls below the terrain surface will be cooler for the most part than surfaces above.
      3. Natural ventilation is restricted as the flat does not get affected by the natural forces of air flowing past the external envelope or by air entering at low level and peculating through to high level – the dynamic effects of air movement to a static area are transferred due to differences in the density of air at low level and high, as well as the external air movement drawing air through (Pitot & Flue/Stack effect)
      4. Water will always follow gravity, going down around your sub terrain with significant hydraulic pressure as well as all the other ways water travels – capillary, absorption, desorption, osmosis. These may not penetrate through your envelope but may get part of the way reducing insulation at some points causing localised cooler points that enable dew on the surface or subsurface.
      Air is the significant factor in making a difference to damp issues as it is the primary conduit to dispel excess moisture from living activities. Even on a hot humid day exchanging of the air in your property is in my view advisable as you will need to balance all the other vapour contaminants in the air you breathe.
      In a very humid hot climate your easiest choice is air conditioning, an experiment I would like to try is to flow external air through a spray of water (droplets not nebulised), providing the water is cool this will condense vapour out of the air as well as absorb other contaminants.
      The above considerations are from my experience and hope it helps your way forward

  2. beatrice says:

    What would you suggest for chronic condensation in a single glazed mobile home?
    I also get “cold spots” behind large pieces of furniture even though they are not placed directly to the wall (sofa, bookcase, bed).

    I am considering buying a de- humidifier as I know that long term I cannot “cure” the condensation which to be fair is really only a problem in wintertime


    • pj says:

      Hi Beatrice,

      This is something that we would be able to come up with a solution for, however, we would need some more information to be able to help out fully. As a preliminary suggestion, the use of a Warm Air Bathroom Fan installed into the main area of the mobile home, with a Dryvent B 12V installed into the bathroom/toilet area to create an airflow through the mobile home, inhibiting any moisture from forming.

      If you would be so kind to call us in the office, which is open from 9am-5pm Monday to Friday on 01189 669090 and speak to either Ray or Peter.

      Thank you,

    • Peter Dickason says:

      Dear Carolyn,

      It is possible for us to ship to Australia. If you could email us ( with your address, then I can get a quotation for yourself.

      Kind Regards

  3. Sharon Taylor says:

    Dear Ray
    I have a fist floor 1930s flat which is one of 32 in a purpose built block. There are two flats above me and a ground floor flat below . The living room and one of the bedrooms share walls with an adjacent flat but all the other walls are sort of detached ie do not have anything next to them.

    A number of flats suffer with condensation and some do not have a problem. However, I believe that my flat is the worst in the block. I am considering installing your fans to the bathroom and kitchen but I did wonder if the fans could also be installed in bedrooms and should like your advice on this?

    Many thanks, Sharon

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