IDEAL House – New Zealand

Project Goals: Certified Passive House, Positive Energy & 8/10 Homestar design. Proudly supported by IDEAL Electrical Suppliers.

Heat exchanged ventilation


With consent hopefully days away, we finalise the details for the ventilation system. We’re using a Passiv Haus certified system from Germany, called Zhender.

The Zhender system will bring in fresh air from outside, and pass it through a heat exchanger venting warm/humid air to the inside – but keeping the energy in the home. This is a balanced system, and quite different from the common Positive Pressure systems which often force air in from your attic into the home, and force the warm air outside. The system we have chosen has hard ducting, not the flexible type which can trap dust and dirt, and are impossible to clean, and has a retail value of around $14,000+GST, plus another couple of thousand for professional installation and commissioning. In fact, you can’t buy these “out of a box”, as the airflow has to be properly balanced. In some respects, it’s the heart of the home and will ensure excellent air quality, which we’ll be monitoring with CO2 and humidity sensors thanks to the assistance from the University of Auckland.

Click here for the designs which show where the system extracts the air (bathrooms, laundries, kitchen) and where it feeds it back in again. Being completely sealed from the outside, we maintain our air-tightness.

Other documents on the system you can download:

ComfoAir CA550 (note we’re installing the slightly smaller ComfoAir 350).

Spec Sheet – ComfoPipe


Spec Sheet – Flat 51 Manifold

Spec Sheet – Flat-51 Ducting

Spec Sheet CK300 Duct

Zehnder ComfoAir_brochure

6 thoughts on “Heat exchanged ventilation

  1. Good start! Couple of questions, though: with the ceiling void, you’ll have to work against stack effects. How is it ensured that e.g. the air that gets sucked out from the ensuite on the top level comes from the rooms on the same level – not from below (which could leave the rooms on the top level insufficiently extracted)? What transfer openings are used? Why are some rooms within the thermal envelope not part of the ventilation system? Entry, corridors and store seem to lack any designation. According to PH requirements, all rooms within the thermal envelope need to either be extract, supply or transfer spaces.
    Speaking of the thermal envelope: where are its limitation on the upstairs floor, e.g. is the plant room within or outside of it? If it is within: where then is the boundary of the thermal envelope?
    A good exercise is to have plans and sections that make the thermal boundaries crystal clear, as everything within the boundaries needs to be conditioned, and where ever there is a boundary needs to have three functional layers that need to be continuous and clearly identifiable.

  2. Can you please estimate how much it will cost to run this system? I mean, assuming you’re paying about 24 cents for electricity (I know that your electricity will actually be free). Or how about, how many units of electricity does it use a day/month? Thanks.

    • Hi, we’ll be paying about 35c per kW, and selling back around 17.5c. The Zhender will use about $75 to run for the year, and recycles most of the energy in the home (fridge, dryer, appliances, and just body heat).

  3. Can I ask how much the unit costs? It seems every heat exchange ventilation company requires a visit before giving you a quote (no doubt to do with the specifics of the house), but I’m interested in just a ball part figure, especially as I’ve never heard of Zhender before. We’ve looked into a SmartVent system which was quoted around $4,500. Thanks

    • Hi Chris, I would say you would be looking around $12,000 plus GST, and installation/commissioning another couple of thousand on top of that. Money well spent though, good heat recovery ventilation would be one of the first things I’d design into any new house. Worth reducing the overall house size by say 5-6m3 to pay for it.

      • Thanks for the reply. Yes I agree they’re great inventions and it seems in many parts of Europe they’re more or less standard – it’s a pity we’re so far behind here in NZ. We were hoping to retrofit one into our old villa but it looks like the price will hold us back. Definitely something we’ll invest in for a future home.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s