" . . . instead we were told that Energy efficient, dual pane, low-E, vinyl windows that were impact resistant would be installed."

What documentation (in writing) do you have that states this?

Mark, there is a signed feature sheet in our purchase agreement that states these exact things. Elsewhere in the Agreement it states that the sliders will be PGT and the windows CGI. CGI Sentiniel are dual pane impact; Sparta a 0.31” monolithic laminated panel consisting of two pieces of glass and a sheet of vinyl, fused together.

The builder installed Sparta. Both are aluminum framed (which if insulated glass was used (“dual pane”) wouldnt be an issue but with only one pane of glass, is problematic because it conducts moisture, especially during the winter months.

Allegedly CGI had developed a vinyl dual pane impact window but when PGT bought them out they wouldnt let them take it to market because it would compete against an established PGT product line. Point being that maybe they intended at the start to install dual pane but when they decided not to produce them they chose the less expensive alterntative.

It would never make sense to replace new windows. Not financially, not environmentally.

I don't know how far you are from the coast but anywhere in that area, temperature differential between inside and outside is not that high. So insulation doesn't matter that much.

This is a point that many don't grasp but you certainly might.

Right this moment, Orlando is 76 degrees (Daytona is 79). For the next week, it is not forecast to be above 90 or below 75. Indoor temp 75 degrees means there is almost no differential. Highs above 100 are rare - maybe 20 times in recorded history. Even at 100, the differential is only 25 degrees.

As far as lows, 27 is the lowest recorded in the last decade. And of course that was for 1 hour, 1 time. Typical winter lows are 50. Again 25 degree differential (or less) from indoor temp. And that is again for a few hours. And that is only Jan, but Feb it is warmer.

Your primary concern is air infiltration to limit humidity transfer into the house. Secondary concern is minimizing solar heat gain. Those windows are probably not great at that but that is significantly more important than the u value. The other issue is layout and design - ie minimizing East and West facing windows and having appropriate overhangs on South windows. Again - way more important than u value of a window in Florida.

If you are worried about future energy costs - install solar. For less than the cost of new windows, you can probably just pay a monthly connection fee most months.

I agree with millworkman that the windows have laminated glass; they are not double-pane or dual-pane windows. You didn't get what you bargained for. It's up to you to decide what is an acceptable compromise.

Does the manufacturer have a stated R value for these windows? How does that compare to similar dual pane windows. I suspect these are better than standard single pane windows but by how much?

Based on the information that you provided, what you have is a laminated glass unit consisting of two 1/8" lites, one of them with a LowE coating, bonded to a .090" interlayer, resulting in a .31" or 5/16" (not 3/16") mono-laminated impact unit in your windows,

CGI refers to the Sparta as an "affordable" impact window option, despite builder comment about using only premium products. Not saying that it's a bad window, just that it isn't what I suspect most people would consider as a premium product.

While I personally think that quoting from a dictionary is at best unduly patronizing, there are technically two panes of glass with a LowE coating in your windows. However, like millworkman and CRH noted, no one in the glass or window industry is going to refer to a window glazed with a mono-laminated glass unit as dual-pane when part of a window system. That's total B$.

When a LowE coating is in an actual IGU insulating glass unit), or commonly known as a dual-pane, the coating improves both U factor and solar heat gain (SHGC) performance over a noncoated dual pane window. When located inside of a laminated glass unit the coating will still block solar heat gain comparable to when in an IGU, but will have no effect on the U factor. Being inside the IGU totally negates the U factor improvement of the coating resulting in performance no better than not having the coating at all.

Often when installing a mono-lami in an impact window the glass manufacturer will use a surface 4 coating, such as Pilkington's Energy Advantage, or Cardinal's i89, to improve the U factor performance of the laminated unit. Generally using the surface 4 coating will improve the U factor performance to U .5 or so versus the U 1.0 that you are seeing....more than adequate for your climate. Clearly, this is not the path that your builder choose to follow.

Personally, I would push for a little more than the $2400 offered but not because of the dual pane claim, but because you have aluminum and not vinyl (assuming that you have that in writing). Despite dual-pane not being an industry term for a lami unit, arguably there are still two lites in the lami unit, so it could be argued that technically they are correct, even if it is B$ as I said earlier. But vinyl is vinyl and aluminum is still aluminum and that can't be argued.

I also agree with David Cary, that in your climate the U factor performance isn't the biggest concern, but I would rank solar heat gain as primary not secondary. Also, aluminum frame is a lot better at conducting heat than is vinyl, so that's a consideration as well.

I also don't think that you need to change your windows, but I would push the builder for compensation for the contract violation (if you have it in writing and not verbal, but also because the dictionary thing would have totally pi$$ed me off.

Check the limits in your local Small Claims Court. $6500 in my area. Simple and quick.

Your builder is full of it. You have impact-resistant SINGLE PANE windows. They are NOT dual pane which is a GAP-INSULATED window. He needs to replace the single pane sashes with the contract-specified dual pane windows. This is on him for not doing the job right in the first place, not you.