Until now we have made due with single pane windows because we have had a wood stove to off set the drafts. It has become increasingly difficult to deal with the rigors of maintaining the stove, so we hope to improve our comfort while resorting to fuel oil as our only heat source.

Our tiny cottage is located in central Massachusetts. The south side of the house is nestled under 50 year old sugar maples which cool the house in the summer and allow in bone-baking heat from the winter sun through a wall of windows. We would surely hate to lose the solar heat gain and so thought to put high solar heat gain windows on the east and on the south. From reading forums on the internet it looks as though Cardinal glass offers low-e windows that will suit in the form of LoE-180. We will put the more conventional LoE2-272 glass in north- and west-facing windows. We will order the glass through Marvin since we aren�t comfortable using a local shop because are not knowledgable about windows.

Though the i81 coating seems to slightly reduce visible light and solar heat gain, the marketing would have us believe that it will greatly reduce precious heat loss. It is a very new coating and we are usually not ones to buy anything that is not tried and true, but we�d hate to miss out on a great efficiency. But then, we have been used to a great deal of light and warmth from the sun through clear glass and worry that the coating will impart a darkness.

We understand that it is not possible to put the Low-E 180 coating on side #3 (where it belongs) AND put the i81 coating on side #4. The Cardinal chart shows that they would put the 180 coating on surface #2 with the i81 coating: The VT would drop from 79% to 71%, Reflectance would increase from 15% to 22%, SHGC drops from .69 to .59, and IP increases from .26 to .24

Has anyone any experience with this coating? The only reference I could find to it is a caveat written for a Passivhaus presentation which cautioned people but there was no further explanation as why the need for caution. It might have had to do with the loss of solar heat gain and nothing really to do with the coating.

Out cottage is 820 s.f. with 16 windows so there is a lot of exposure for good and bad for us. Skip the i81? go for it?

Any advice is welcome.

Regards, Deb

Very nice to see a customer so well informed.

Given the exposures and shadings as you have detailed them, I am not sure the i81 is such a great addition to the 180 glass package.

Something that is not often discussed with the hard coat low-e is the drop in condensation resistance when compared to the standard soft coat, dual pane low-e.

If you have any condensation issues now, I would be leery of the hard coat low-e option.

Being totally clueless about how to calculate such things, we are trying to figure out if the solar heat gain will off set the price of heat loss without the i81 coating. Any idea how to get a rough idea about that?

Given that you are going to be tightening up the home, winter condensation issues will be more likely per the reduction in air changes and leaks. I would be cautious with the hard coat low-e option and probably stay with the 180 on the exposed sides as originally thought of.