Humidity in Your Home

Let’s face it. Today’s modern homes constructed to the current Ontario Building Code, or better, are basically giant plastic bags. Maintaining fresh air on a continuous basis becomes extremely important. That is why we provide our homeowners with two sources of fresh air, windows that open and a fresh air machine that we install, also known as an Energy Recovery Ventilator (ERV) in every new home. While we suggest that homeowners are able to open their windows whenever they wish, it is imperative to remember to run the ERV whenever the windows are closed. That is why we recommend leaving the unit running on “Smart Mode” at all times. This enables homeowners to control the flow of fresh air into their home all year round.

However, this “Giant Plastic Bag” also results in the need to manage humidity levels far more than an old leaky home. We are now more concerned with too much humidity in the home, rather than the home being too dry. Understanding what is happening and having good strategies for dealing with household humidity is essential to your home’s performance.


Controlling your Mechanical System? Like driving your car!
We commonly describe to our customers that operating their mechanical system is a lot like putting your car in drive, or as we would say “Set it and forget it!” This refers to picking a home temperature and leaving it consistent as well as putting your ERV control on Smart Mode. However, just as you must alter how you drive according to changing weather conditions, it is also important to understand that we must alter how the home’s mechanical system is operated based upon weather conditions.


Changing Weather!
Another factor impacting our homes is that our weather is becoming more and more unpredictable. It seems like we can go from fall temperatures to the depths of winter in a matter of a few hours. This can play havoc with the humidity levels within your home from one day to the next. This winter in particular has seen several rapid fluctuations. One day it is plus 5 Celsius and overnight it can drop to minus 10 or even lower.

When this occurs, it is very common for your home to take some time to adjust and homeowners often panic when they see a high humidity reading. I hope that this blog will help to give you a better understanding of what is happening within your home and how to manage it more effectively.


What is “Relative Humidity”?
Relative humidity is a way of describing how much humidity there is in the air, compared to how much there could be. When the temperature is warm, more water vapour can be in the air than when it is cold. If the actual amount of vapour is compared to the total amount there could be, as a fraction, then the resulting number tells if the air feels dry or moist. The value is usually written in percent, where 0% means that the air is totally dry, and 100% means that it is so moist that mist or dew is about to form. When the temperature is lowered a lot, the relative humidity increases and the water vapour can turn into condensation or precipitation, as dew, rain or snow (etc.). (Source Wikipedia).

Think of a glass of ice water in a warm room. You end up with water on the surface and someone invented coasters and napkins to manage this condensation. That is a great way of showing that relative humidity can also vary within the same room. The rest of the room is not raining water, only at the colder surface area of the glass.

The same is true for windows. If you were to take a humidity gauge that can be aimed at a surface, you might find that the interior wall of a room is showing 33% relative humidity, while the window surface is much higher, maybe 47% if it is a cold winter day. The colder the outside temperature, the colder the glass temperature. If the surface of the glass gets cold enough it can result in water condensing on the windows.


Water Condensation on Windows, is it good or bad?
Actually, it can be both. If it is a cold winter’s day, a small 1” band of condensation across the bottom of a window, shows that you have humidity present in your home and that would be a good indication if it is a really cold day. A home that is over dry creates a different set of problems. However, if that same window has 4-5” of condensation and begins dripping is a different matter and should be addressed, as it is a good indication your humidity levels are too high. One of the greatest benefits of the warm edge spacer between the glass panes is in keeping the glass warm enough so that condensation is much less likely to occur. The benefit to you the homeowner is that there is less chance of having moisture damage. That is also why we are introducing triple glazed windows to our customers.


Preventing mold growth in your home
While there are health risks to living in a home that is over dry, that is seldom the circumstance with today’s tighter homes, especially when they are using an ERV for ventilation. As previously noted, we are more concerned with excess moisture in the home. The Ontario Building Code recognizes that a good range for humidity levels within the home would be between 35-50%, with 35% being more optimal in the winter time and 50% more common in the summer. During an extreme cold snap, the home may need to have the humidity reduced to 30% or even 25% for a few days. During a hot summer heat wave, that humidity level may climb up into the 55% range. That might feel a bit clammy and you may wish to reduce your humidity levels. However, if the home begins to go above 60% relative humidity and stay there then you have conditions for mould and this needs to be avoided all year long. It only takes a few days for mold to begin to grow, so if excess humidity is noted, then it is important for measures to be taken quickly to get the relative humidity back into the normal range.


Why Triple Glazed Windows?
Triple glazed windows come standard with our Net Zero Ready homes. One of the biggest advantages of using triple glazed windows is that the triple glazing will keep the surface of the window warmer and allow for a higher winter time humidity level within the home. This becomes a great advantage on really cold days as the homeowner is able to maintain a much higher (40%) relative humidity in the home without having the same type of condensation issues of a double glazed window. This helps to keep the home healthier and more comfortable.


Controlling Winter Humidity
As I noted above, in the winter time, there may be days where the outdoor temperature plunges dramatically. When this occurs, the window glass will also get much colder relative to the rest of the home. In this case it may take the home a few days to adapt to the colder temperature. Under this condition, it can be common to have an excess build up of water vapour on the windows, even resulting in pooling.

Should this occur, it is best to wipe up any standing water and then deal with lowering the home’s relative humidity to manage the levels and reduce the condensation on the windows.

It might take several hours depending on how rapid the change in temperature was and how cold it is outside. Here is an example: If we were able to transport outside air (using your ERV) that is 10﮲C and at a relative humidity of 80%, into a room that was at 20﮲C, the relative humidity would fall to around 40% as the air warms up in the room. If you bring enough outside cold air into the home then you can reduce the overall humidity of the air in the home.

This can be done by opening a window for an extended period of time but this will make the home colder, you will not be comfortable and it will cost more to reheat that air. That is why we recommend using your ERV on MAX for a high humidity winter time event.


Controlling Humidity using your ERV
A simple, more effective way to reduce your indoor relative humidity levels is to use your ERV. Often times we find that customers are afraid to use their ERV control because they might not be confident in getting to the answer they need. So here are three simple steps to control humidity using your ERV that everyone can do.

First: Select Smart Mode by pushing the “Smart” button on the bottom right of the ERV Platinum control. This is always located in an open area of the main floor.

Second: On the ERV Platinum control there is an up arrow and a down arrow. If you press and hold the up arrow for about 8 seconds it will display the relative indoor humidity. If it is higher than it should be, then you know you need to take action. The relative humidity can be displayed by holding the up arrow for 8 seconds.

Third: Rather than trying to remember how to change the settings on the platinum control, an easier way to do this is leave the principal ERV control on Smart Mode, and run the bathroom control for an hour or longer. This way it will revert back to the Smart Mode setting without having to change the main control setting. If you still need more dehumidification, then repeat running  the bathroom control.

If you would like to know more about using your ERV for ventilation and dehumidification, then watch the video below as it demonstrates how to use the ERV control.  


Controlling Shoulder Season Humidity (Spring and Fall)
This circumstance can be a bit more challenging to manage because on some days the home can fluctuate from needing heating at night to calling for cooling in the afternoon. This makes for a situation that can be very difficult to manage. If the outdoor temperature is 10C or less then the same dehumidification through ventilation strategy of using your ERV will still be effective. However, once the outdoor temperature is between 10C to 20C, the home is losing less heat, but not requiring cooling, so the system becomes somewhat less effective. On a cool dry day, this is less of an issue, but if it is a cool humid day, then the home can become somewhat clammy as the outdoor air is more humid than the indoor air, but too close in temperature to provide adequate dehumidification. This weather does not usually last for extender periods, rather it tends to occur for a few days at a time during the shoulder season until the clear, dry air of a high pressure front pushes out the damp air from the area.

During this type of cool weather, high humidity event, it may be necessary to supplement dehumidification to keep the home from climbing into the danger zone. In this case running a dehumidifier in the basement for a few days might be a perfectly acceptable option. Note that this will always be a more expensive way of controlling humidity, so it should not be the first choice, but rather a last choice when other options will not work due to outdoor conditions.


Controlling Summer Humidity
In the summer time, the ERV will reduce the amount of humidity entering the home as it exchanges inside air for fresh outside air, however it can still add humidity to the home. In very high humidity events, it might be beneficial to put the ERV on recirculation mode during the daytime when the temperature is hottest and back on smart mode when the sun goes down and the need for fresh air is the greatest. In addition, maintaining a temperature in the 21-23 C range will have air in the home that is able to hold a higher level of humidity than if you were to try to over cool the home down to 18-19C, which can result in a cold and clammy feeling on your skin.

However, during the summertime, the best form of dehumidification will come from your Air Source Heat Pump working in Air Conditioner (AC) mode. In this case we want the AC to have long run times. When the system runs on short run times (under 15 minutes), it will short cycle, by satisfying the temperature call at the thermostat, but not supplying enough dehumidification. It takes significantly longer run times to actually provide significant ventilation. Because we are providing a system designed to operate very efficiently in this situation, it is a good thing if the AC runs for longer than 15 minutes or longer when it turns on. This will control the humidity and provide for a more comfortable living environment.


Do I need a Humidifier?
Depending on how you live in your home, there may be a need to add humidity. During the wintertime, the ERV is pulling very dry air into your home at the same time as it is exhausting stale moist air from the home. While this is not likely that using your ERV will over dry your home there is still the possibility of over-drying occurring, particularly if you don’t cook (boil water) or shower enough to add moisture to your home.

If you notice that your hardwood or trim is starting to pull apart, or that your skin is dry and itchy or you are starting to get nose bleeds, this is a very good indication that your home is too dry. Indoor plants are a good way to help balance the humidity in your home, but not if you turn it into a green house.

While we recommend against adding a humidifier, if your home is continuously below the recommended humidity level and the options mentioned above have not worked, then you may need to consider adding a humidifier.


What does this all mean to you, The Homeowner?
It is important to remember that this is meant to be a guideline and that each home will act in its own unique way and that you will need to get to know your home and learn how to manage its operation.

There are multiple variables that could impact on how your home is acting and often homes will act differently from one neighbour to another. Your home could operate very differently than your neighbours. Items such as size, number of occupants, how the home is used, orientation of the home on the lot, number and size of the windows, type of home, finished basement and age of the home can all impact upon how it reacts. And it is important to understand that it can vary throughout the year. That is why it is important to understand controlling humidity. It is also good to understand that relative humidity levels will react with natural products such as wood. A home that is over dry can lead to cracks between wood trim or floor boards. A home that is too humid can result in hardwood that is cupping.

One final thought! No different than how we must change the oil and filters on our vehicle every 5,000 km in order to keep it working as it was intended, it is also important that you as the homeowner will need to maintain the home’s HVAC system so that it operates as intended. We recommend the following maintenance for your HVAC system:

  • Change your furnace filter monthly while construction is in the area. Use a filter with a cardboard frame and a pleated filter. This is stronger and has more surface area for collecting particulate.
  • Wash your ERV foam filters at the start of each season.
  • Vacuum your ERV core once a year or twice a year if needed.
  • Keep your outdoor intakes and exhausts free from dust and debris. Check these at the start of each season.
  • It is also important to ensure your Exterior ERV hoods are not blocked after any large snowfall.

A well maintained HVAC system plays a key role in helping you maintain your home’s humidity at the optimal levels and help to provide you with a healthy, safe and comfortable living environment.


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We just wanted to let Mr. Tarry know that our experience with every single member of his team has been nothing but amazing.  We started looking for a new home 2 years ago and spoke to Amanda Joiner here in Strathroy at the open house.  We left her office that day 2 years ago and we knew DTH was a perfect company for us to trust with our future. Amanda made us feel  comfortable and she was very helpful in every step of the way.  We can’t say enough good things about her.  We bought one of your quick possession homes on Rushby St and could not be happier.  Jason took us through the house for our final inspection, and again he was amazing.  So friendly and informative.  Took his time going over everything and explaining it all and answering questions.  We also met Joe, I believe he is the site supervisor.  Joe, again so friendly and goes out of his way to make sure we where happy. Daryl and Laurie in your customer care centre are phenomenal.  They have been nothing short of amazing.  I’m sure you probably realize that you have an amazing team working for you but sometimes when you hear it from an outsider it means a little more.  So we applaud you Mr. Tarry for assembling such a great group of people to represent DTH.  They are doing an amazing job for you and treating all of your customers like they are family and we appreciate it.  Thank you to all at DTH for making our experience nothing but AMAZING.


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We chose Doug Tarry Limited as the builder for our custom home because of their reputation for quality workmanship. Having our new home built at the same location as our current home we were able to witness first-hand the skill, quality, and pride of workmanship that each tradesman working on our home put into their work. We have had so many positive comments on the design and layout of our home, as well as the quality of the products used within the complete design. We cannot be happier with the finished product, and we highly recommend Doug Tarry Limited to anyone thinking of building a home.

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After purchasing many new builders homes, the Doug Tarry experience was by far the most enjoyable. With the team’s recommendations, ideas and perfectionism, we ended up with a home that far surpasses any of our expectations. When we woke up after the first night in our new home, we both looked at each other and said “this feels like home”. We have never had that feeling after the first night in any of our previous homes. After 6 months we still at times say to each other ” Man I love this house”. Great work Doug and crew.

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Living in Nashville TN for just shy of 3 decades I decided to return to my hometown of St Thomas to semi retire.  I had never considered building a home especially with living at such a distance during a build.  Upon meeting Michelle at the showhouse in Miller’s Pond, visiting the décor centre with amazing choices and learning more about the quality and energy efficiency of Doug Tarry homes I jumped in with both feet during a week visit.  I purchased the lot, set my design choices in motion and left to wrap things up in Nashville leaving my build in the capable hands of Doug and his teams.  I opted for the Glenwood and from the day I moved in I haven’t had one moment of regret.  I’m so happy with every aspect of my home, the quality of the build and fabulous customer service. I love my new neighbourhood and have made some great friends.  Thank you for making my move a much smoother transition than I could hope for. 


Thank you Doug Tarry Homes for our wonderful home. Throughout the planning and building stages we found everyone we dealt with to be extremely knowledgeable and helpful. Any concerns or issues were promptly dealt with in a professional manner. The quality of our home, both inside and outside, is exceptional. (Even after one year we haven’t found a nail pop!) You go the extra mile and it shows. We would not hesitate to recommend Doug Tarry Homes to anyone.

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We greatly appreciate all your sincere efforts in helping us build our dream home. On behalf of our family, thank you once again and I look forward to seeing you around!


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This current home is actually my fifth new home I’ve lived in. I wouldn’t hesitate to build again with Doug Tarry. The standards for the home – insulation, framing, kitchen, plumbing, etc – are very high compared with other builders. This allowed me to put some additional funds into some extras, such as recessed lighting and hardwood flooring. The Doug Tarry group work very much as a team, from the home plan design, interior selections to sod. You are very much supported in the entire building process, and the follow-up for any issues after you move in is excellent.


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I knew our new house was energy efficient but not that much! At the time of construction, we decided to insulate the basement floor instead of me getting a cold storage cellar. We have a very efficient furnace with an ERV unit. It wasn’t that cold in December, but even with all the kids home for 2-3 weeks over Christmas, our gas bill was just under $40! Love it.

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We were into our new house yesterday! What a wonderful surprise to see the welcome gift basket!! We have been so impressed all along with Doug Tarry homes, from the people (you!), the quality of the house, the design, the materials, the basement, the air and temperature of the house, everything!! Liam used to build houses and he has been blown away by everything we’ve seen and experienced with Doug Tarry homes. He’s not easily impressed either and has a keen critical eye and he is over the top happy with everything, as am I. So a big thank you Michele, for everything. You’ve been so patient with us right from the beginning, when we first showed up over a year ago when we first started looking at the area in St Thomas.

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Don and Pat