If a passive house is designed well is it worth the extra cost for Low E window coatings?
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.
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.
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, when done right, it can lead to greater interior thermal comfort. We have a page that explains everything you need to know about window selection, have a read here first -
How to choose the best windows for High Performance Homes
There is a lot to it, and it is honestly best left to those who do energy modelling. An example to look at would be our LEED V4 platinum Edelweiss House where we employed a very comprehensive passive heating and cooling strategy in our 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.
And remember that maximising 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 or you'll be spinning your wheels and spending all you heat savings on AC in the summer. That is all explained here in our Passive solar home design video series.