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If a passive house is designed well is it worth the extra cost for Low E (High solar gain) coatings?

Joe Van Kuren Published: June 7, 2019, 8:37 p.m.Last updated: June 13, 2019, 11:21 a.m.

Assuming the windows are appropriately facing south and the entire design is sound with thermal mass and good overhangs would double or triple glaze Argon filled windows be appropriate without the Low E coating?  The Low E coating does reduce the solar gain even if you choose a coating designed for the northern climate.  (I am in Ontario 44 degrees north).  My application would have 5x5 ft fixed windows with 5x2 foot awning style windows below and above for ventilation.

Responses (1)

Mike Reynolds
Mike Reynolds June 13, 2019, 11:05 a.m. Reply

 

Hi Joe,

Low-E coatings are something we always recommend whether you’re installing double or triple glazed windows. So when you talk about having a Passive House well-designed, Low-E coatings would be a big part of that solution, so no, we wouldn’t recommend omitting them as a way to save a bit of cost. They will help reflect heat back in during the winter and help reflect heat back out in the summer. So it will save on heating and cooling costs, and if you don’t use air conditioning then it will lead to greater interior thermal comfort. 

We employed a very comprehensive passive heating and cooling strategy in our LEED V4 platinum Edelweiss House, and we had different coatings on the north windows compared to the south. The south windows were a lower R-value, so they do lose more heat in the night, but the Low-E coating was chosen and applied in a way that they would gain far more heat in the day than they lost, so in the end they offer a net heat gain. north windows will offer virtually no passive heat gain, so you want the highest R-value windows possible to reduce heat loss. 

Of course increasing your southern exposure for passive heat gain needs to include a passive cooling strategy such as overhangs or sun shades to prevent overheating in summer. And depending on the proximity to your house, you may also be able to count on mature deciduous trees as shading as we did with the Edelweiss House, that is a great part of a passive heating and cooling design as the leaves shade you in summer but allow the sun to warm your house starting in the fall. 

We have a few pages that may be of value to you, such as our pages on designing for thermal comfort, choosing the right windows, everything you need to know about Passive House,  and this first episode of our Passive solar home design video series.

 

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