Frequently asked questions about SEVi ductless Heat Recovery Ventilation

For what type of building is the SEVi HRV System made for?

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Why shall I use a mHRV System when I can open the windows instead?

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Can I install the SEVi HRV System during the refurbishment of my existing home?

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How can I get heat recovery without a heat exchanger?

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What´s the difference between the SEVi HRV System and single room ventilation?

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How many units do I need for my building?

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How much do I have to pay for electricity to run the SEVi HRV System?

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What do I have to expect in regards to maintenance of the SEVi HRV System?

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Can I get bad air quality caused by germs and bacterias?

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Will the SEVi HRV-System influence my well being?

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Is the SEVi HRV System suitable for allergy sufferers?

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Will the SEVi HRV-System regulate the humidity level in my building?

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What kind of noise creates the SEVi HRV System?

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Do I have to expect draughts, by having the SEVi HRV System installed?

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Does the SEVi HRV-System affect the usage of my stove or fireplace?

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Is the SEVi HRV System certified?

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What is the life expectancy of the SEVi HRV System?

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What kind of warranty will I get?

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I need more than six HRV-Units for my building, how can I control them?

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What about the extract ventilation for bathrooms?

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What do I have to prepare for the installing of your HRV-System?

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What´s the advantage for the use of the pre-fab casing ?

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Can I extend your HRV-System in case of house extensions or changings?

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What does the ALD 160 Background Ventilation Unit mean?

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Any questions left?

Please get in touch with us.

The SEVi HRV-System is made for any kind of buildings with certain sizes, no matter if they used for residential or commercial purposes. 

Bear in mind that you need a certain quantity of units when you want to ventilate your complete building. This quantity needs to be assessed by the size and the total number of occupiers. 

Please do not expect that two SEVi 160 HRV Units will ventilate your complete building with 200m² or more.

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Especially in well insulated buildings you have to secure a permanent supply of fresh air. Sure you can try the purge ventilation by opening the windows, but you have to do this constantly in the winter time, to allow the moisture to get out. Who want´s to do this, by knowing of losing heat/ energy by opening the windows always?

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Yes, of course! The SEVi HRV-System needs no ducts and pipes - it´s the perfect solution for subsequent installation. There´s no need of extensive labour, like when getting ductwork installed.

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Each SEVi HRV-Unit blows the stale air for roughly 75 seconds out of the room. The air is passing the built-in heat buffer, made of special ceramic, which get´s heated by the energy of warm air, leaving the building. Afterwards the SEVI-Unit changes the working mode and sucks fresh air into the building for another 75 seconds. This fresh, clean air has to pass the heated ceramic buffer on its way to into the building  and gets heated this way. 

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A single room system is just ventilating one room of your house by having very limited options for distinct adjustments. Some of these systems are running 50 minutes per hour on a passable ventilation mode but 10 minutes every hour on a so called boost mode, which is very noisy. Also, there´s no option for controlled interaction between these units whenever you have more than one installed.


By using the SEVi HRV System, you´ll benefit of a sophisticated ventilation system which can be upgraded or extended every time.

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It depends on the size of the building. You need at least a minimum of two SEVi HRV-Units because they´re operating on an inverse principle. One unit blows the stale air out and the other one sucks the fresh air in until they change their working mode after 75 seconds.


For an average 3 bedroom house, you should expect between 6 and 10 SEVi HRV-Units, depending on the size and proportioning. 

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Compared with the most centralised hrv systems you´re saving money on the running costs. The SEVi HRV-Units run on low Wattage - the average consumption of electricity for a complete system of 6 units is less than €30 per year (based on a unit price for electricity of 20ct/ kWh). Also there´s no energy consuming heat source involved. The SEVi heat recovery principle works at temperatures down to -20°C without noticable condensation.

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That´s the biggest advantage of the SEVi Ductless HRV System! Because it operates without ducts, there´s no need for expensive duct cleaning and sanitizing by using specialists with dry ice or other chemicals. The SEVi HRV-Units are made to maintain just by the user with conventional cleaning devices. For example the ceramic heat buffer is made for cleaning in an ordinary dishwasher.

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Because of  the short length of our  SEVi HRV-Units  and the permanently change of the air flow, there´s no chance of breeding germs. Just clean the SEVi HRV-System every 6 month and replace the filters constantly and enjoy the fresh and clean air every time.

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By getting supplied with fresh and clean air constantly, you´ll feel much better especially when you awake in the morning. 

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We supply different filter types for the SEVi-HRV Units. Beside the standard one, you can get a special pollen filter to reduce the risk of hayfever. Or you can choose a charcoal absorber to protect yourself against the most of the enviromental toxins. Our filters are easy to reach and replaceable without hassle. A small light on the control panel will give you notice when it´s time to Check or change the filter.

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Due to the permanent air change, you´ll get a decrease of humidity inside of your building. You can check this fact usually in the winter time at your window panes, by having less (or none) condensation there.

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Every SEVi HRV-Unit runs on a noise level of less than 20dB on the lowest fan mode. This sound level is comparable with a cooling fan, as installed in your computer. 

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No, because the SEVi HRV-System is engineered to operate almost unnoticed. There´s also an additional wind damper available, which can be implemented in units, operating in highly exposed areas.

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In some exceptional cases it can happen, that you have to install a separate pressure monitor for fireplaces. This device will switch off the SEVi HRV-System during the operation time of your fireplace, to prevent dangerous lack of air pressure inside of your building. Please ask us, if you´re in need of further details about such a  monitoring system.


In general - we highly recommend the use of stoves / fireplaces with external air supply only.

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Every SEVi HRV-System is designed and manufactured in Germany, that´s why it´s certified and approved by German authority bodies like DIBt. Furthermore the performance of the system is tested by independent institutes like TZWL e.V.

Please ask for copies of the certificates in case you´re interested in more details. The certification contains the CE label as well.

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The first SEVi HRV-Systems were built more than 17 years ago and they´re still running, because of the usage of high quality parts like EBM-Papst fans or high-end ceramic heat buffers. And for the worst case - the part exchange is very easy to handle.

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You´ll get a full 24 months warranty against manufacturers faults and a 10 years warranty for the performance ot the ceramic heat buffer units. The warranty excludes all damages, you´re responsible for by yourself.

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Our standard control units SEC 20 and SEC 20 basic operate up to 6 SEVi HRV-Units. If your system consits of more than 6 SEVi HRV-Units, you´re in need of 2 (or more) SEVi standard control units.


Since 2015 we supply the new SEC-Touch, a touch screen operated control unit which operates up to 12 SEVi HRV-Units. This new unit offers much more comfort, because you can adjust different ventilation zones for your building.

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We offer a wide range of matching extract fans as well as a special single room ventilation unit with heat recovery. Please ask for the SEVi Duo Mini, in case you want to ventilate your bathroom in a high efficient way with heat recovery.

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If you want to install the SEVi 160 HRV-System, you need core drillings of 165-180mm. The external diameter of every unit is 160mm but you should leave a joint arround, which has to be proper sealed afterwards to prevent thermal bridges or sound transmission. If the blockwork is not finished or you have to do massive changings on your external walls, we highly recommend the use of our pre-fab casings (Mounting Aid) instead of core hole drilling.

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The pre-fab casing is mostly made for new buildings and will be installed during the block laying. When it comes to the second fixing of our SEVi HRV-System, you just have to put the unit in the existing opening of the casing. It fits perfect and ensures a proper insulation around. By using the pre-fab casing, you don´t need an additional core drilling.

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Of course. You only have to connect the new SEVi HRV-Units to your existing control panel or to install another SEVi Control Panel, in case you already run the maximum amount of SEVi HRV-Units on the existing SEVi Control Panel(s).


If you want to built your SEVi HRV-System stepwise, we recommend the usage of our Background Ventilation System "ALD 160".

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Our Background Ventilation Kit is similar to a conventional vent but offers various advantages.

1. You can upgrade the Kit into a full SEVi HRV-Unit, just by installing the Finishing Kit afterwards. All you need is the wire connection to the (existing or prospective) SEVi Control Panel.

2. The Preparation Kit contains the same external hood and  internal cover like the complete SEVi HRV-Unit. You get the same high-quality parts and the intake of air in a controlled manner.


By using the Background Ventilation Kit in conjunction with a pre-wiring, you can upgrade from a Passive Ventilation System (which is needed to ensure the standards for well-insulated homes) into a ductless SEVi HRV-System step by step.

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