You’ve heard that a passive home doesn’t need a furnace, so what’s the deal with air source heat pumps?
HVAC in a Passive Home
A passive house doesn’t have a furnace, but it does have two essential components for heating and cooling (heat pumps) and air circulation (an ERV or HRV).
The ERV or Energy Recovery Ventilator is what we like to call a fresh air machine. Required in new home builds in North America since 2017, ERVs manage air quality and moisture. (We don’t tend to use HRVs as they don’t handle moisture, but they are an option in very arid climates.)
An air source heat pump handles both heating and cooling year round by pulling heat energy and transferring it. In the winter, the heat pump pulls available heat energy from outside and warms it further; in the summer it pushes heat energy from the home outside. It uses very little energy to do this.
Deciding on the best heat pump arrangement for you new passive home is the focus of this article. In the photo of EkoBuilt’s model home shown here, the mini split unit for the air source heat pump is shown at centre, at the top of the wall in the main living area.
Affordability is key
The mini split single head has a corresponding exterior unit, which is shown on the south-facing aspect of a two-storey EkoBuilt home here.
We find that a single mini split unit per floor works extremely well in all of our passive home designs.
In our experience, a single unit for up to about 2,000 sq ft of open concept floor space is ample to provide the heating and cooling required by one of our homes. We place that unit in the main living area of the home, finding that most people prefer to sleep in cooler conditions.
Only the most extreme heat or cold conditions (e.g. an extreme polar vortex) might cause a need for supplementary heating in bedrooms.
Our own model home provides one example of how to provide supplemental heating to rooms that tend to be used less.
Building code in the province of Ontario requires an approved HVAC design to be in place before a building permit will be issued. That code dictates that every bedroom or secondary room (office/den) in the home needs its own direct source of heat. We satisfy this requirement with electrical baseboard heaters, which we find we never use.
This obviously adds a little to the bottom line for the project for Ontario homeowners, but we still find that this approach is very cost effective.
It’s a very real option for homeowners wanting to ensure a source of supplemental heat in exceptionally cold conditions.
HVAC design for a passive home
A passive home provides the opportunity to drop the reliance on fossil fuels and the larger energy footprint of older homes, instead choosing to make use of air source heat pump technology.
Although most other provinces and states don’t have Ontario’s requirement for an HVAC design before a building permit can be issued, we do recommend having an HVAC design for your passive home early in the process.
Taking the time to create an HVAC design for your new home will make it much easier to get accurate pricing on your home’s build from local contractors.
The HVAC design will also provide a blueprint for where key elements should be placed and make the whole process clearer and easier.
HVAC decisions for your home
We feel it’s important that the homeowner decides on the approach taken to HVAC design.
Our passive weathertight material kit or shell provides the basis of the home, and then HVAC elements are integrated depending on the home’s size, layout, and personal preferences.
Given that a furnace isn’t required, we tend to be looking at ductless systems, but the makers of air source heat pumps do offer ducted systems (Zuba Central from Mitsubishi is one option).
There are options to implement multi-zones systems with an air source heat pump system, controlling temperature differently by zones or rooms. Used correctly, this can create efficiencies, but it’s more complex and costly to implement upfront, and most suited to very large homes.
We tend to end up advising on the following options:
- Single head mini split system** – approx $12.5k for the system, with the option of additional heads at roughly $2 – $3k each.
- Ducted / Ductless ASHP (mini splits) with up to 6 zones – approx $20 to $22k for the system.
- Forced air heat pump system – approx $25k for the system.
**Most EkoBuilt floor plans and homes are perfect with option number 1.
Still not sure what’s best for your new home? No worries.