ᐅ Decentralized Mechanical Ventilation – Yes or No? Pros and Cons?

Dear Forum,

We are currently planning our new build, and I have now received the scope of work from our builder. First of all: one thing is certain, a central heat recovery ventilation system is out of the question because it is too expensive.

The basic data for our single-family house:
130 sqm (1,400 sq ft), underfloor heating on the ground floor and in the bathroom (upper floor), radiators everywhere else, all windows with roller shutters (thermally insulated roller shutter boxes with half-shells).

[U]According to our scope of work, the following is to be installed:[/U]
"Decentralized ventilation system Lunos e² with heat recovery (up to 90%), very low power consumption (only 0.09 watts / sqm (0.008 watts / sq ft) thanks to direct current), and a 10-year warranty on the ceramic heat exchanger. Fully integrated into the exterior wall. Exhaust fans as AB 30/60."

[U]Our wall construction is as follows:[/U]
- Double-shell facing masonry – total thickness of 45 cm (18 inches).
- Inner leaf – 17.5 cm (7 inches) thick aerated concrete blocks as plan bricks, WLZ 0.10, compressive strength PP2, brand Ytong.
- 14 cm (5.5 inches) hydrophobic (water-repellent) core insulation boards KDII with staggered joints, WLG 035.
- 2 cm (0.8 inches) air gap.
- 11.5 cm (4.5 inches) facing brick.
- U-value is approx. 0.16 W/m²K.
- Triple-glazed insulating glass as thermal insulation glass (Ug value 0.7 W/m²K).

Is it really necessary to install a heat recovery ventilation system? I know it prevents mold and ensures controlled air exchange. But is it really required? I am rather skeptical about it. I have already been in several houses (built from 2013 onwards) without heat recovery ventilation and haven’t noticed anything negative.

So far, the disadvantages outweigh the benefits for me (just my own opinion):
- Increased energy use (electricity, heat loss).
- Holes in the wall.
- Noise from external influences and the ventilation system itself.
- Energy loss during winter.
- Higher temperatures in the bedrooms during summer.

If we decide to go with a decentralized heat recovery ventilation system, how many fans would be needed? Where would it be advisable to install them?

Thank you in advance for your effort and opinions!!!

You actually lose more heat without a ventilation system... so that’s a misconception.

Only a ventilation technician can tell you how many fans you need, but for an efficient system, it usually comes down to one fan per room or multiple fans in larger rooms.

In that case, a central ventilation system is not that expensive and often even cheaper.

If you can maintain regular ventilation intervals, then you don’t need a mechanical ventilation system. Your architect can advise you on this. Typically, this means opening windows wide for 5-10 minutes daily in the morning and evening for air exchange.

I can’t manage that because we also have other tasks and work to do, so we installed a ventilation system in our house and have had no regrets so far.

So now I can share some real-life experience – we have a decentralized mechanical ventilation system with heat recovery.

Mechanical ventilation with heat recovery is definitely recommended – there is no more musty or stale smell, not even in the morning. Opening windows for ventilation is unnecessary. When it’s cold, the system also reduces humidity. We woke up to 55% humidity (after a night on level 1 with two people in the room) and now it’s back to 48% upstairs (after a few hours on level 4).

Disadvantages: Levels 3 and 4 are, in my opinion, only for parties, assembling furniture, or if you are hard of hearing. It also works when you are on a different floor. If a plane flies by outside (not sure why planes ever fly there, but it happened last week), you can hear it a little.
Level 2 is suitable for everyday living (unless you are alone and pay close attention).
Level 1 is fine for sleeping.

Electricity consumption is probably balanced out by the heating savings – I’m not sure if that’s really the case; however, these systems don’t use much electricity.

That rather speaks in favor of a central controlled ventilation system for living spaces – I never understand why anyone would install a decentralized system in a new build...

Hello,
I moved in four weeks ago and am using the Lunos e² ventilation units together with exhaust fans in the bathroom/WC and kitchen. For 175m² (1,884 sq ft) of living space, we have 8 e² units with heat recovery and 4 exhaust fans across 3 levels. Just give the manufacturer Lunos in Berlin a call—they provided me with excellent advice. From what I can tell after four weeks, the indoor climate is very good. With four children, regular airing out three times a day would have been impossible, so a heat recovery ventilation system was absolutely necessary.
At level 1, you can easily sleep; levels 2 and 3 are only used as needed. For the exhaust fans, I would recommend the RA15/60 instead of the WB30/60 because it consumes less electricity, is quieter, and has 3 instead of 2 speed settings. I would also consider installing a TAC controller (well explained on their website), which allows you to control the entire system easily. Otherwise, the exhaust fans are controlled individually and the e² units in groups of four.
Feel free to ask if you have more questions.
Regards,

Sorry, but this is really complicated – why not just install a central ventilation system? People try so hard to make the house airtight, then end up drilling half the facade full of ventilation openings.

And then you constantly have to adjust settings depending on the time of day or whether someone is home?