Blog Post

6 Ways to Ventilate Your Home (and Which is Best)

How a green home really “breathes.”

Should a green home require a piece of ventilation equipment like our  Zehnder HRV?

Photo: Alex Wilson
One of the features in our new house that I’m most excited about barely raises an eyebrow with some of our visitors: the ventilation system. I believe we have the highest-efficiency heat-recovery ventilator (HRV) on the market—or at least it’s right up there near the top.

Why ventilate?

For centuries homes weren’t ventilated, and they did all right, didn’t they? Why do we need to go to all this effort (and often considerable expense) to ventilate houses today?

There are several reasons that ventilation is more important today than it was long ago. Most importantly, houses 100 years ago were really leaky. Usually they didn’t have insulation in the walls, so fresh air could pretty easily enter through all the gaps, cracks, and holes in the building envelope.

Also, the building materials used 100 years ago were mostly natural products that didn’t result in significant offgassing of volatile organic compounds (VOCs), formaldehyde, flame retardants, and other chemicals that are so prevalent in today’s building materials, furnishings, and belongings.


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Ventilation options

Ventilation can take many different forms. Very generally, systems can be categorized into about a half-dozen generic types:

A ventilation system schematic from the Building Science Corporation fact sheet on balanced ventilation.

Image: Building Science Corp.

  • No ventilation. This is almost certainly the most common option in American homes. There is no mechanical system to remove stale indoor air (and moisture) or bring in fresh outside air. In the distant past, when buildings weren’t insulated, this strategy worked reasonably well—relying on the natural leakiness of the house. It’s worth noting, though, that even a leaky house doesn’t ensure good ventilation. For this strategy to work there has to be either a breeze outside or a significant difference in temperature between outdoor and indoors. Either of these conditions creates a pressure difference between indoors and out, driving that ventilation. On calm days in the spring and summer, there might be very little air exchange even in a really leaky house.
  • Natural ventilation. In this rather uncommon strategy, specific design features are incorporated to bring in fresh air and get rid of stale air. One approach is to create a solar chimney in which air is heated by the sun, becomes more buoyant, and rises up and out through vents near the top of the building; this lowers the pressure in the house, which draws fresh air in through specially placed inlet ports. The rest of this blog post will focus on mechanical ventilation.
  • Exhaust-only mechanical ventilation. This is a relatively common strategy in which small exhaust fans, usually in bathrooms, operate either continuously or intermittently to exhaust stale air and moisture generated in those rooms. This strategy creates a modest negative pressure in the house, and that pulls in fresh air either through cracks and other air-leakage sites or through strategically placed intentional make-up air inlets. An advantage of this strategy is simplicity and low cost. A disadvantage is that the negative pressure can pull in radon and other soil gases that we don’t want in houses.
  • Supply-only ventilation. As the name implies, a fan brings in fresh air, and stale air escapes through cracks and air-leakage sites in the house. The air supply may be delivered to one location, dispersed through ducts, or supplied to the ducted distribution system of a forced-air heating system for dispersal. A supply-only ventilation system pressurizes a house, which can be a good thing in keeping radon and other contaminants from entering the house, but it risks forcing moisture-laden air into wall and ceiling cavities where condensation and moisture problems can occur.
  • Balanced ventilation. Much better ventilation is provided through a balanced system in which separate fans drive both inlet and exhaust airflow. This allows us to control where the fresh air comes from, where that fresh air is delivered, and from where exhaust air is drawn. Balanced ventilation systems can be either point-source or ducted. With ducted systems, it makes sense to deliver fresh air to spaces that are most lived in (living room, bedrooms, etc.) and exhaust indoor air from places where moisture or pollutants are generated (bathrooms, kitchen, hobby room).
  • Balanced ventilation with heat recovery. If there are separate fans to introduce fresh air and exhaust indoor air, it makes a lot of sense to locate these fans together and include an air-to-air heat exchanger so that the outgoing house air will precondition the incoming outdoor air. This air-to-air heat exchanger—more commonly referred to today as a heat-recovery ventilator or HRV—is the way to go in colder climates. A slightly different version, known as an energy-recovery ventilator (ERV), doesn’t transfer moisture (often an advantage when a house would get too dry in the winter or too humid in the summer).

I’m a firm believer that all homes should have mechanical ventilation. With better-insulated, tighter homes, that ventilation is all the more important. But even in a very leaky house, one can’t count on bringing in much fresh air or calm days in the spring and fall when there isn’t a pressure differential across the building envelope.

If budgets allow, going with balanced ventilation is strongly recommended, and if you’re doing that in a relatively cold climate, like ours, then providing heat recovery is a no-brainer. Mechanical ventilation always takes energy; with heat recovery the energy penalty of fresh air is minimized.

Alex is founder of BuildingGreen, Inc. In 2012 he founded the Resilient Design Institute.

Published February 5, 2014

(2014, February 5). 6 Ways to Ventilate Your Home (and Which is Best). Retrieved from

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June 20, 2022 - 9:57 am

Balanced ventelation  means balanced intake vs exhaust. Thg only reason radon might enter into a home is if your mechanical ventelation exceeds your mechanical fresh air intake thereby creating a "negative pressure or vacuum" in the house sucking gases up through your floor drains. That is why you need it balanced....equal pressure ..maybe a touch more pressure to accomadate exhaust fans for the kitchen and bathrooms.........

November 8, 2020 - 6:30 am

Building an adobe home using lime floors. The architect and numerous articles recommended against a vapor barrier in the floor because studies have show the barriers push the vapor outward to the walls and can cause mold problems at the base of the walls. "Breathability" was the watch word. Built up floors with 2 feet gravel for capillary break, geomembrane, compacted fill, insulation, then 4" Natural Hydraulic lime slab. Still getting lots of moisture vapor through the floors. Seems like a bad idea to put a concrete type sealer of the lime floor before applying the final finish. Any recommendations on how to reduce moisutre vapor coming up through the floors or is this a venting issue to resolve?

September 6, 2020 - 12:35 pm

Hi! I'm building a new home office and need to figure in heat and ventilation. I do solder as well as use some glues and other not so nice chemicals (not very often) I believe we are leaning toward a high efficiently mini split for the heat. We have propane here. I don't need ac in this space as it's very cool in being in the basement, sometimes much too cool! What would I need to be sure I'm getting proper ventilation and good air quality in this space? I have 1-2 employees and my toddler who are frequently in this space. I planned to do some type of ventilation directly at the solder/glue station. Do I need more? Any suggestions are appreciated because I know nothing about this!

February 19, 2020 - 3:45 pm

B. Perry: I think an HRV would work much better than the Humidex unit you describe. The Humidex does not appear to actually exchange indoor air with fresh outdoor air. I would also suggest that you consider replacing the windows where condensation occurs, or adding storm windows—especially if the windows you describe are single-glazed. If you are getting the level of condensation you describe on insulated (double-glazed) windows, then I think you should have a weatherization expert, energy auditor, or building science expert take a look at your house; you may have a significant moisture source that you are not aware of. As starters, ventilation should always be used when showering, and avoid drying firewood in your basement. A balanced ventilation system, such as a properly commissioned HRV, should not contribute to a radon-entry problem, though use of a heavy-duty kitchen range hood fan could still result in negative pressure when that fan is operating. I hope this is useful.

February 19, 2020 - 12:56 pm

My house, in Canada that was built in the 90's did not include an air exchanger or HRV but did come with a Humidex ventilation system installed in one of the rooms in the basement.

The Humidex does not work very well.  My windows sweat pretty bad during the winter months and black mold grows on the bottom of the windows where the water gathers.  The Humidex also does not work well in reducing humidity in the house when the outside humidity is high.  Also since the Humidex creates a negative pressure in my home it may pull more radon gas into my home since the interactive map for radon gas in my area says my home's location is a medium risk for potential radon gas.

So I am thinking of replacing my Humidex with an HRV or ERV to help with the moisture, but I am not sure if these balanced ventilation systems will increase or decrease the chances of radon gas being pulled into my home. .... Can you please explain?


B. Perry

October 22, 2019 - 8:59 am

Mrs Ooi, I would highly recommend a second opinion on this. If the house is airtight (and it should be), there will not be fresh air coming in without windows open. Good luck!

October 21, 2019 - 3:47 pm

You're right but when I asked him about this, he says that his own house doesn't smell and the air is fresh. Therefore the ventilation systems is not useful. He also stated that because MHRV produces a fixed temperature, it might be too hot to sleep in but comfortable in the living spaces and vice-versa. Is that true? Thanks

October 21, 2019 - 9:05 am

Mrs Ooi, this is not my area of expertise, but I am skeptical that a house can be properly ventilated in winter with "cross ventilation" unless the windows are open! Where is the fresh air coming from?

October 20, 2019 - 3:57 pm

Thank you for your article. We're planning a new build and have met with the builder/architect. He said that he's not a proponent of using things like Mechanical Ventilation with Heat Recovery (MVHR), ventilation systems etc. His argument is if a house is well designed, well sited with good cross flow ventilation, then all of these systems are negligible. He says that you only need 1 gas fire for winter with the houses he designed.

We went to a house he built for his client. It did have decent cross ventilation and no HRV type systems too. Apparently the while of last winter, they didn't use the 2 heat pumps and only used the lone gas fire in the living and the house was warm. Now these clients are like me ie lived in a freezing house so anything newly built would be far warmer anyway due to increased insulation and double glazing.

He is not the first building designer that I have met in my journey who are not fans of the passive house movement. Moreover, many say that building a passive house in Auckland, New Zealand is an overkill as it's not that cold compared to maybe South Island in New Zealand. I am confused now so any comments please to help clarify things? I don't want to build a new hpuse and find my energy bills higher than my old house and still suffer from the cold in winter.

April 9, 2019 - 8:55 am

What would be my best option for fresh air ventilation in 1 bedroom only in a 3,500 sq ft home? 

February 18, 2019 - 8:11 pm

Sorry to hear you are cold! Especially THIS winter!

Is the fan your attic powered and is it continuously running? If so, the fan is actually depressuring the attic. If this is the case, the warm moist air from your living space is being drawn into the attic to try to equalize that pressure.

Also, the vent should remain open. It’s near impossible to actually stop the natural flow of warm moist air entering your attic from the living space so the vent helps to flush that out.

I’m generalizing as I dont know exactly how things have been set up. Please feel free to message me. I’m happy to help.

January 7, 2019 - 1:56 pm

I insulated my entire house this past fall, I was told by the engineering company I needed an exhaust fan in the attic or they couldn't provide the insulation.  I agreed and now that's its winter...its freezing in my house!!  I went into the attic and turned the fan off and closed the vent, which is in the living room, not the bathroom. It's helped a bit but it's still very chilly.  I thought the insulation was going to save me money!!  Very disappointed in this entire process!!

January 2, 2019 - 11:14 am

I do not see a problem retaining the gable-end peak vents even when you are relying on soffit and ridge vents for your house. This extra venting if you are venting a full unheated attic seems like a good idea. If you have an insulated roof and only a vented airspace under the roof sheathing, relying just on soffit and ridge vents makes more sense.

January 2, 2019 - 11:04 am

I'm not sure about air filtration or air-exchange add-ons to a ducted HRV or fan-coil system, but you might consider a separate, through-the wall (i.e., non-ducted) HRV for your apartment where you can control the location of the air inlet. The Lunos products, distributed by 475 High Performance Building Supply is one option: A system like this might do the trick.

Ideal, in your situation, might be a through-the-wall HRV in which the incoming airflow could be set to be greater than the outgoing airflow—so that you are creating positive pressure in the apartment and, thus, preventing uncontrolled air entry. I don't know if that is an option with these systems, but you may want to ask about that.

December 23, 2018 - 4:21 am

Hi.  I am having a lot of problems with secondhand smoke drifting into my condo unit.  I am very sensitive to the smell of it.  I have read many resources that recommend an HRV or ERV but the condo board has flatly refused stating that there is no place for the ducts.  Is there a smaller system that can be installed to an existing heat pump or fan coil system in a condo unit to pressurize it?  Thank you

August 25, 2018 - 9:38 am

I have been told to close vents in peaks of house and only have roof vents and soffit vents. Is this correct? 

July 16, 2018 - 11:58 am

Hello Scott,

Without learning a little more about how you insulated your 1940 house, it's hard to comment. A solar attic fan can help draw warm air out of an attic, but there need to be air inlets for effective exhaust to occur. When you say that you covered the vents that's a little troubling—especially if you're referring to the soffit vents under the eaves.

Also, relative to the original article, be aware that an attic exhaust fan is not a whole-house ventilation strategy; it is only designed to ventilate some of the hot air from an attic—and it's effectiveness for even doing that is questioned by some building science experts.

May 29, 2018 - 10:23 am

i recently put 1'thick insulation and hardy board on my house.  i covered up the vents that were on there on the north and south side.  i just put on the roof a solar exhaust fan.  will that be enough to suck out all the hot air in the attic?

thanks Scott

April 7, 2017 - 7:24 pm

With a friend, I built a beautiful deck around my house (500m2), in australian hardwoods....I live in Sydney, on the northern beaches area....which has become more tropical, with global warming.

Approximately 100m2 of the deck, is around 8-10" above the ground and approximately 200m2, is just 4-6" above the ground. Obviously there is no air flow....consequently, when the rains come...the decking remains wet on the bottom, then drys on the top....hense, due to the expansion the 140mm wide boards, close the gaps between the boards and start to 'cup' the boards. Over that period i have had a constant battle with the contraction (summer) and expansion (winter). I have run a circular saw blade down the joins, in the worst cupping areas....however some large 'ugly' gaps appear in the worst of a dry summers contractions.

After the joint cutting...the expansion still closes the gaps between the boards, but the cupping 'may' have subsided.....3 years after installation.

There is a creek at the rear of the the ground water level is normally quite high, therefore the surface soil can be quite damp during the wet periods.

I don't have the option to raise the deck off the, I am looking for an external solution.

I am currently looking at installing some kind of mechanical a 6" fan, placed under the deck, with the outlet connnected to my rear fence (open to a reserve).....the inlet open, to hopefully draw some of the damp air and moisture from under the decking.

My question to you/your colleagues is: would a 6" fan (rated at 490m3/hr), be sufficient to draw air from under the decking. My fear is that the fan will just draw air from the gaps in the decking or nearest opening.....rather than from the furthest darkest wetest areas.

I realise that it's difficult to capture all of the peramaters, but any guidance would be much appreciated.

Thanks and regards,


April 28, 2015 - 2:57 pm

We bought a house in Hot Springs, Arkansas, in 2010 that has had a continuing issue of excessive moisture readings and moldy smells, primarily in a west and south facing corner. The house is on a slab. We first thought pressure washing created the problem, then a poorly fabricated flagstone patio was a suspect. Uncaulked windows were also an item of interest. We have had two sessions of mold remediation, pulling built-ins and drywall, etc. Both times mold was treated and or the drywall/insulation, etc. was removed. We also removed the flagstone, installed a French drain and replaced the patio with a concrete surface. We also improved the diversion of water away from the foundation. Additionally we have noticed unexplained high moisture readings in an east wall. We were told the east shrub bed was too high, so we pulled the shrubs, lowered the bed, replaced the shrubs and installed a French drain in the space close to the house. My wife still complains of a moldy smell in that area. The house sits relatively high sloping away and water should be moving away from the foundation. Several "experts" in fixes for our problem have come by, but most can't determine the source of moisture. We wondered if poorly installed vapor barrier in the slab construction is the problem, but the wood floors remain in good shape. The roof is cap vented. I have usually had wind turbines, but generally the homes in this area are capped. We had a wet summer last year and so far, a wet spring. Moisture readings for our suspect areas are about 12% in the drywall. What would you recommend to resolve our problem?

April 30, 2015 - 10:17 am

Here's a quick explanation of what a hygrothermal assessment can tell you about a moisture situation.

April 29, 2015 - 9:36 am

John, I'm sorry to hear about your troubles. Based on my conversation with Peter Yost, our resident building scientist, it sounds like you've done a lot of work that was a good idea anyway, even though it doesn't seem to have solved the particular moisture issue of concern. So that's a great start.

There are building science experts who perform hygrothermal analyses of homes. Most of the specialists who work with moisture control are NOT the same specialists who work with mold remediation. This is how you've ended up in a situation where you've remediated mold twice without actually finding the source of the moisture; unlike the drainage work you've done, that was a waste of your time and money. What you need is a building science expert. Peter is one of a handful of people who consult on this kind of work (he'll be writing to you separately to discuss). I'm working on posting a PDF he put together on what a hygrothermal analysis actually entails; if you hire someone to help you, that person should be familiar with the same principles. I'll post a link to that document later today. It's likely you will need to find a building scientist who can investigate the problem at your home.

As a side note, Peter mentioned that your moisture meter may not have been dialed to the drywall setting for the 12% reading. Drywall is so dense that it is completely saturated at 2% moisture content; after that it just becomes a slurry. It was likely on the setting for wood.