Passive House Cooktop & Range Hood Exhaust
The Cost to Install
The major difference between an electric induction cooktop and a natural gas cooktop is the cost of the ventilation system.
Natural Gas Cooktops
Oh the glory of the flame! There is no question that there is something undeniable about cooking on an open flame and so we are not saying you can't put a gas cooktop into a high performance home or building. However, be forewarned, it is not a cheap endeavor and here is why.
First, the combustion process from a gas cooktop will produce significantly more particulate matter including carbon monoxide, nitrogen dioxide, carbon dioxide, acetaldehyde and formaldehyde. These pollutants must be exhausted directly to the exterior of the home by a range hood. When exhausting that much air out of a home, this changes the internal air pressure balance where more air is being exhausted than supplied into the home. The problem with that is what is called infiltration. These homes are airtight, but not 100% airtight and so the risk is that in the winter, cold outdoor air will be drawn into the exterior walls and roof of the house where it will hit warm interior surfaces and condense into water. Water, walls, roofs. Not a good mix, dry is good.
So, to counteract the risk of infiltration, the Building Code requires what is called make-up air ventilation. This additional fresh air is intended to offset the range hood exhaust air ultimately providing consistent internal air pressure balance.
So what does all of this mean? Well, here is a list of the parts required to make this system work.
Gas Cooktop Exhaust Ventilation System Parts List
1. Insulated exhaust duct connected to range hood
2. Motorized damper electrically activated by range hood
3. Tape for interior envelope penetration
4. Tape for exterior envelope penetration
5. Exterior wall cap
6. Metal flashing at head and sill of wall cap
Gas Cooktop Make-Up Air Ventilation System Parts List
1. Bulkhead or dropped ceiling with grille to conceal system
2. Insulated intake duct
3. Motorized damper electrically activated by range hood
4. Force flow electric resistance heater to heat up cold incoming air
5. Tape for interior envelope penetration
6. Tape for exterior envelope penetration,
7. Exterior wall cap
8. Metal flashing at head and sill of wall cap
That's a lot of parts that have to be installed and coordinated by numerous trades. The real kicker is that every time you turn on the range hood, you are literally dumping air, or energy, out of the house that you just paid to heat. On top of that, the make-up air has to be heated while it is sucked into the house to keep the temperature of the house consistent. That's a double whammy of additional ongoing operating costs every time the fan is turned on.
So to summarize, gas cooktops are possible in high performance homes. We have done them, and will most likely do them in the future as we appreciate that the cooking with gas is a nice experience. That being said, when considering the pollutants created, the initial construction and ongoing operating costs, we suggest considering electric induction cooktops for a number of reasons.
Electric Induction Cooktops
More Energy Efficient - Yes
Fewer Pollutants - Yes
Cheaper to Install - Yes
Cheaper to Operate - Yes
With electric induction cooktops, air-borne pollutants are reduced which allows for a much simpler approach to exhausting the pollutants created.
Number one, we still include a range hood but rather than connecting it to a duct that exhausts directly to the exterior, we use a re-circulating range hood with a charcoal filter. The filter removes any immediate pollutants and the remaining air is exhausted through the homes ventilation system (HRV/ERV). An exhaust diffuser is located above, and no less than 6'-0" away from the cooktop to prevent any fats or greases from being sucked into the system.
The advantage of this approach is that the internal air pressure balance inside the home is not altered, therefore, all of those additional ducts, dampers, heaters, wall caps, etc. that are required in the natural gas based system are no longer needed.
Electric Induction Cooktop Parts List
Every high performance house has a cooktop, range hood, and a ventilation system so it doesn't cost you an additional dime for this system to work brilliantly.
When cooking, simply hit the boost switch and the flow rate of the kitchen exhaust diffuser is increased from a continuous 27 CFM to 35 CFM (46-60m3/h). Additionally, the entire house ventilation flow rate is also increased which aids in flushing the entire home. That may not seem like a lot of air but in reality, a high performance home will completely flush all of the air throughout the house at least 8 times in a 24 hour period without even hitting boost. Now that's fresh air!
Admittedly, and it needs to be said that this approach is not as fast at exhausting pollutants as a ducted range hood which is typically a minimum of 150-200 CFM (254-340m3/h), however, because the number of pollutants created are reduced and there is a direct path for the polluted air to be constantly exhausted from the home, this approach is 100% guaranteed to work no matter who is living in the household.
We bring this up because with a ducted range hood, regardless of the cooktop type, the homeowner still has to remember to turn on the range hood! This may seem obvious but the statistics showing how many people can't be bothered to turn on the range hood because they either don't care or simply don't want to listen to the noisy fan are quite surprising.
If you are considering or in the process of designing a high performance home we will recommend an electric induction cooktop with a recirculating range hood and continuous ventilation system due to its considerably lower cost and reduced indoor air pollutants.
Regardless, we understand that everyone has a preferred method of cooking and all that we can do is to inform you of the potential advantages and disadvantages of either approach.
Our job is to make sure whatever your choice, the system is designed and installed correctly to ensure that you have fresh air, 24.7.365!
Certified Passive House Designer
NIDO Design Inc.
High Performance Modern Home Design - Prefab - Build
Kelowna, British Columbia, Canada
1. Energy Impacts of Effective Range Hood Use for all U.S. Residential Cooking. Jennifer M. Logue and Brett C. Singer. Environmental Energy Technologies Division June 2014
2. Ultrafine particles and nitrogen oxides generated by gas and electric cooking. M Dennekamp, S Howarth, C Dick, J Cherrie, K Donaldson, and A Seaton. 2001
3. BSI-070: First Deal with the Manure and Then Don't Suck. Joseph Lstiburek. 2014
5. Uncut and Hoodwinked: The unintended consequences of monster-size range hoods. Robert Bean. 2013
6. How to Provide Makeup Air for Range Hoods. Martin Holladay, Green Building Advisor.com, 2015