When Can Low-E Be A Problem?

To all the glass experts and fenestration experts out there...PLEASE READ! 

Only a 3 minute read!

When can Low-e be a problem?

I have always stood by the fact that Low-e glass is the single most important option in a window. Whether replacing the window or just the glass in any region. 

Within the last few years I have found a problem with it. Not a big enough problem that I still wouldn’t recommend it...but a problem nonetheless. 

I mostly replace glass for a living, and within the last few years something has come to my attention. Low-e glass can reflect off of a window and melt vinyl siding on houses, burn holes into patio furniture, or even in some cases start fires. 

I have been replacing glass in a certain subdivision in central Michigan for about 13 years. I received a call about 6 years ago that the reflection off of a window on a house was melting the siding on a neighbors house. 

My original thoughts were that someone must have been mistaken. 

Until I saw it for myself. 

What happened was the sun reflected off of a window onto a house close by, and the Low-e in the window was doing its job and reflecting the heat instead of going into the home. The concentration of heat off of that window went across the house throughout each day with a high enough temperature to actually melt the siding leaving a path of melted vinyl behind. 

I had a laser temperature gun with me so I took the temperature of the siding where the sun spot was. The temperature at that time read 139 degrees Fahrenheit. The siding without the sun spot was at 82 degrees Fahrenheit. If I remember correctly it was about 72 degrees that day. 

Whose fault would this be? 

The builder? The siding company? The window manufacturer? Either of the two homeowners? 

Did the builder put the houses too close together and at the wrong angle? 

Is the siding made too thin or too dark where it cannot absorb heat over a certain temperature without melting? 

Is the window manufacturer at fault for having the Low-e perform too well where it is causing problems?

I have been asked these questions over the last few years. 

In this subdivision alone there are at least 15 cases of siding melting from nearby windows. In one case I went to a house where there were holes burned into the patio furniture on their own deck. It was their kitchen window with Low-e (all windows that I speak of have Low-e in them) that was reflecting down to create burn marks as you would see if a cigarette was left to burn out on the cushion of this chair. There were about a dozen burn holes. 

I was sent there by the window manufacturer to replace the glass. Before I started to replace the glass I put my hand into the reflection and felt the heat beaming down off of the window. It was very hot. I changed the glass in this kitchen window to grey tint with Low-e. Afterward I felt a major difference in temperature. The reflection (faint now) was not hot anymore. The glass must have been absorbing most of the heat instead of reflecting it onto the furniture. 

In my opinion this is the solution in cases like this. I have since changed other windows to tint/Low-e that were causing this problem and it has helped in every case. (Not solar grey tint as this reflects similar to a mirror.) 

I have done some reading online and read where there has been a few cases where this reflection has started a fire in the right circumstances. 

Has anyone out there had to deal with this same problem?