ᐅ Controlled residential ventilation & heat pumps: Viessmann vs. Vaillant vs. Zehnder?

Created on: 23 Nov 2022 14:12

Technician in red overalls on ladder repairing an outdoor air conditioning unit on a house.

Hello everyone,

I want to revisit a topic that was mentioned a while ago in another thread but deserves a more detailed discussion, as it turns out to be more complicated than anticipated. Here’s our situation, and I would really appreciate hearing about your experiences. Starting with the background.

We are currently building a prefabricated house (timber construction) with a prefab home manufacturer. The plot is located in a small village, in a very old part of town. It seems like almost everyone heats with wood there. On our property, there is a wood smoke smell throughout the entire winter (we noticed this last year already, and it’s happening again this year), as if there is a campfire burning nearby non-stop.

Now, we are seriously concerned that with a mechanical ventilation system with heat recovery (MVHR), the indoor air could end up smelling the same as the outdoor air, which we definitely want to avoid. To counter this, we thought about installing a mechanical ventilation system with an activated carbon filter included. That’s why we have tentatively selected the Zehnder ComfoAir Q350 TR in the enthalpy version, since both of us already occasionally suffer from dry eyes. This system also comes from the factory with attachments for activated carbon filters.

Unfortunately, things turned out differently than expected. The house supplier is hesitant in initial discussions and is postponing the topic until the customization meeting in December. The reason given: they only work with Viessmann or Vaillant because the heat pumps come from those manufacturers. More precisely, it would be either the Viessmann Vitovent 300W or the Vaillant recoVair VAR360 ventilation system. Neither of these original systems offers a solution with an activated carbon filter.

Now to my main question. What’s your opinion on this? Our concern is not unfounded, and an F7 pollen filter doesn’t seem to be an adequate solution for this situation, does it? They immediately said that an F7 filter would be sufficient, but we don’t believe that.

Is it possible to install a Zehnder mechanical ventilation system alongside a heat pump from Viessmann or Vaillant, or not?

I don’t want to assume the worst-case scenario, but do you have any ideas on how to solve this problem if the house provider doesn’t allow any other mechanical ventilation system?

I would be very grateful for any ideas, experiences, or tips!

Best regards

Mycraft27 Nov 2022 10:33

#37

For the quantities, the 300 model would be sufficient for the ground floor/upper floor. Although, in my opinion, it is rather tight. If the basement rooms are included (which is recommended, since it is part of the building envelope), it is better to opt for a system one level higher, with a maximum capacity of 400 cubic meters or even 500 cubic meters. This will prevent it from constantly operating at the upper load range.

Nixwill227 Nov 2022 18:42

#38

Thank you both very much!

Unfortunately, I made a mistake in the total values by listing the volume of the upper floor twice. The ground floor volume isn’t 166.89m³ (5890 ft³), but actually 226.36m³ (7990 ft³). @Dogma, this means your assumed 407m³ (14,380 ft³) increases to 467m³ (16,500 ft³). That naturally raises everything even more. And if we also follow the recommendation from @Mycraft to include the other basement rooms, that would add another 115.67m³ (4080 ft³), so we’d actually be looking at around 583m³ (20,590 ft³) 😳.

I’m starting to worry that this will push our budget beyond limits again, since the Viessmann Vitovent 300-W datasheet states that 400m³ (14,120 ft³) is the maximum volume for their largest unit!

What’s strange, however, is that the datasheet says:
- H32S A225 max. airflow 225m³/h (7,950 ft³/h) for homes up to 160m² (1720 ft²) living space
- H32S C325 max. airflow 325m³/h (11,480 ft³/h) for homes up to 320m² (3440 ft²) living space
- H32S C400 max. airflow 400m³/h (14,120 ft³/h) for homes up to 440m² (4730 ft²) living space

I don’t really understand this, our house is definitely not the largest. When I add all the square meters, including utility areas, I get about 235m² (2530 ft²). How can Viessmann specify an airflow of 400m³/h for 440m², while we’re actually calculating more than 500m³ (17,660 ft³) for our “little house”?

It’s also odd that the alternative unit from Vaillant (recoVAIR VAR 360/4) only manages a maximum of 360m³/h (12,720 ft³/h) and they claim it’s suitable up to 290m² (3120 ft²) living space 🤨?

I’m really close to removing the basement entirely from the plan because everything else would just blow the budget even more... 🙁

Nixwill227 Nov 2022 19:00

#39

Dogma schrieb:

@Nixwill2
The number of plate valves is basically determined by the number of rooms. Living and common rooms receive supply air. Bathrooms, kitchen, and utility rooms have exhaust air.

That is very interesting; I wasn’t aware that not every room gets both supply and exhaust air! So, the living room only has supply air, and the exhaust air might be located in the kitchen. Then the next supply air would be in the guest bedroom, with the corresponding exhaust air only in the guest bathroom? Is that how it works when you look at one floor? Does this also work through closed doors between rooms?

Dogma27 Nov 2022 19:42

#40

Nixwill2 schrieb:

Thank you both very much!!!

Unfortunately, I mistakenly listed the volume of the upper floor twice in the total figures, but the ground floor volume is actually 226.36m3 (eight cubic yards), not 166.89m3 (six cubic yards). @Dogma, this means your assumed 407m3 (fourteen thousand cubic feet) increases to 467m3 (sixteen thousand five hundred cubic feet). This naturally raises everything a bit more. And if we also follow @Mycraft’s recommendation to include the other basement rooms, that would add another 115.67m3 (four thousand cubic feet), so we’d actually have about 583m3 (twenty thousand six hundred cubic feet) 😳.

I’m getting worried that our budget will be overstretched again, since the Viessmann Vitovent 300-W datasheet states a limit of 400m3 (fourteen thousand cubic feet), which is their largest unit!

What’s really confusing in the datasheet are the following specifications:
- H32S A225 max. airflow 225m3/h (eight thousand cubic feet per hour) for homes up to 160m2 (one thousand seven hundred square feet) living area
- H32S C325 max. airflow 325m3/h (eleven thousand five hundred cubic feet per hour) for homes up to 320m2 (three thousand four hundred square feet) living area
- H32S C400 max. airflow 400m3/h (fourteen thousand cubic feet per hour) for homes up to 440m2 (four thousand seven hundred square feet) living area

I don’t quite understand this, our house is definitely not the largest. Adding up all square meters including utility rooms, I get around 235m2 (two thousand five hundred square feet). How can Viessmann specify an airflow of 400m3 for 440m2, while we calculate over 500m3 for our “little house”?
It’s also strange that the alternative unit from Vaillant (recoVAIR VAR 360/4) only manages a max of 360m3/h (twelve thousand seven hundred cubic feet per hour), and they say it’s suitable for up to 290m2 (three thousand one hundred square feet) of living space 🤨?

I’m seriously considering removing the basement completely from the planning, because everything else would just push our budget even further... 🙁

This is because many manufacturers calculate nominal ventilation using a 0.5 air change rate and a room height of 2.5m (8 feet). As you can see from their data, it fits quite well:
290m2 (three thousand one hundred square feet) * 2.5m (8 feet) = 725m3 (twenty-five thousand six hundred cubic feet) * 0.5 = 362.5m3/h (twelve thousand eight hundred cubic feet per hour).
In the first two years, I actually ran my ventilation system at a 0.7 air change rate to remove moisture. For the past four years, I’ve set it to 0.3 air changes during the day and 0.4 when all four residents are home. We’ve never had mold, and we didn’t have to use the windows for ventilation. With the F7 filter in the supply air, my 500m3/h (eighteen thousand cubic feet per hour) controlled residential ventilation system only achieves a maximum of 0.7 air changes in supply. The exhaust could handle about 0.85.

Nixwill2 schrieb:

This is very interesting, I wasn’t aware that not every room gets both supply and exhaust air! So, in the living room there is only supply air, and the exhaust air could be in the kitchen. Then another supply vent in the guest room, with the matching exhaust only in the guest bathroom? Is that how it works if you look at one floor? Does supply and exhaust air exchange still work if the room doors are closed?

No, otherwise you wouldn’t get good air circulation in rooms. Place the supply valves as far away as possible from the room doors and use corridors as exhaust air channels, for example, by extracting air in the bathroom.
You can also adjust exhaust valves so that, for example, only part of the air is extracted in the basement, and the rest is drawn up to the ground floor and removed there.

Room doors can be closed if they are not airtight. A gap of 0.5 to 1 cm (0.2 to 0.4 inches) between the floor and door panel is sufficient.

Nixwill228 Nov 2022 16:43

#41

I’m honestly not sure what to do now. The two systems offered by the house builder seem too small for the entire house. They don’t allow any other system (we’ll find out for sure next week during our appointment with them), which basically means I might have to leave out the basement...

I don’t understand this. I don’t consider our house that large. Could it really be that around 150m² (1600 ft²) is the maximum size these two manufacturers can handle...

What would you recommend? Leaving out the basement, meaning no ventilation in the basement?

Dogma28 Nov 2022 21:32

#42

Nixwill2 schrieb:

I’m honestly not sure what to do now. The two systems offered by the house provider seem too small for the entire house. They don’t allow a different system (we’ll find out for sure next week --> appointment with them), which can only mean I’d have to leave out the basement...

I don’t understand. I don’t consider our house very big. Could it really be that around 150m² (1600 sq ft) is the maximum for these two manufacturers...

What would you recommend? Skip the basement ventilation, so no ventilation down there?

What they allow is secondary at this point since you are the one paying. The differences are mostly in how the manufacturers commission the systems, but fundamentally they’re all the same.
I wouldn’t leave out the basement if you’re building new anyway. That’s the best time to hide the ventilation ductwork.
What concessions would they make if you source the mechanical ventilation with heat recovery system yourself?

P.S. Our house is only 140m² (1500 sq ft) plus a warm roof with 40m² (430 sq ft) area, and our Helios mechanical ventilation system with heat recovery is a size 500, which runs at about 50% or 70% capacity depending on the time of day.

ᐅ Controlled residential ventilation & heat pumps: Viessmann vs. Vaillant vs. Zehnder?

Reaktionen