Windows for the Flatrock Passive House.

It has been a while since I last posted.  My excuse....It has been very busy! In this post I figured that it would be a good time to talk about one of the things about a passive house that I still haven't discussed:  Windows.

There are so many window manufacturers, so many different types of windows, so many different types of glass inserts, and so many industry claims.  I was told by by designer, Mike Anderson, that we needed a triple glazed window with a high solar heat gain coefficient.  Where would I find this in Newfoundland?  There are several window manufacturers here but none of them have windows that have the data necessary to modelling in the PHPP software.  Mike suggested Peter Kohler Windows.  I said really?  He said, that a few years back, they did the necessary testing to provide parameters that can be used to properly model heat loss and gain through windows for the PHPP software!.    Such parameters are a measure of the heat transfer through the glass, heat transfer through the frame from inside to outside, heat transfer from the frame to the structure of the house, etc.    Given that each window is like subtracting R-value from the walls, the energy loss/gained through those windows can be quite significant.  In fact once the R-value of the walls goes beyond R20, the major source of heat loss is through windows in the home.

Kohler Energlas Plus windows have a center of glass R-value of 5.6 (metric U-value = 1.0 W/m.m.K.  This is pretty respectable given that most double pane windows with clear glass have a center of glass R-value of about 2 (U-value = 2.83 W/m.m.K).  With respect to thermal loss, a plain Jane window will have power losses on the order of 50% while the Kohler Energlas Plus windows will have power losses on the order of 17%.  Taking the ratio of U-values illustrates that the energy loss for the Plain Jane window is 283% higher than the Energlas Plus window.  To put this in perspective, consider a 1 square meter window (1 m.m) and a 22 degree C (equivalent to Kelvins with respect to difference, K) temperature difference between the inside and outside temperatures.  I chose 22 Celsius since the mean exterior temperature during winter in St. Johns is about 0 C and people often find 22 Celsius a comfortable temperature.  The Plain Jane window looses energy at a rate equivalent of a 62 W light bulb which heats the air in the house and then it literally goes right out the window!  Under the same thermal conditions, the Energlass Plus window only looses 22W!  thats a difference of 40 W!   That same 62 W bulb will now only loose 22 W and the 40 W left over is actually heating the space!  Although the argument is oversimplified, it it does illustrate how passive gains can contribute significantly to interior heating if windows are efficient.  The fact of the matter is that window are typically the weak part of the envelope.  They are equivalent to leaving lights on in your house indefinitely.  Many homes have too many fenestrations.  It is not uncommon for houses to have 19-20 windows.  Imagine if they were each 1 square meter under the same thermal conditions above...1240 W would be going right out the windows! So the 1240 W of your total heat load wouldn't even contribute to would only keep the temperature constant.  Compared to the same situation with triple glazed Energlas Plus windows,  440 W would be lost, while 800 W can contribute to warming.  This is a huge savings.

Kohler vinyl windows are currently listed on the PHIUS site with parameters for PHPP.  There are very few north american window manufactures that have gone down this road so people often pay a premium price to import european windows....this can be a very very expensive venture.  The nice thing about Kohler windows is that, in Atlantic Canada, they are manufactured in Nova Scotia by KohlTech.  Having a manufacturer close to home is good and having dealers in St. John's is even better.  I placed my order with "The Window Shop" ( and they were good to deal with.  Ordering can be confusing with all the options but I just followed my designer's recommendations: Energlas Plus Supreme Casement series of windows ( .

As for doors, they are often more leaky than windows. Steel doors are no exception.  They often warp and leave a gap at the top or bottom.  I opted to upgrade to fiberglass.  In addition, they have a multi point handle set which latches the door at three positions on the door frame to ensure a tightly closed door every time you close it (  Looking through the upgrades I realized that most vinyl doors have a frame that is vinyl clad on wood.  KohlTech has a cellular PVC option which is solid vinyl which is guaranteed never to rot!  Given that I am going to longevity with this house, it seemed like the natural choice.

The order was sizeable, but I went forward with a budget in mind and was willing to take money from other house budgets to maximize the weakest part of the envelope.  Surprisingly, the order came in below budget! by about 25%! I was pleased to say the least.


  1. Great detail there buddy ! It seems that you have all your ducks in a row.

  2. interesting choice for the windows , im also considering the koler windows . would like to know if you choose a HRV yet?

    1. Hi, the Koehler windows are a very cost effective option. As for the ventilation unit, I will be using the x24erv ecm manufactured by Venmar. It has ratings that can be used in phpp according to the PHIUS white papers on using ratings from HVI. From my research, this unit has a rating similar to the zehnder comfoair 350 erv.

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