You need to get several more bids. Those prices are way to high. I had double pane, tinted windows installed for $8k.

Keep shopping. Double paned glass is way overpriced. Typical COST to the dealer/installer should be no higher than $300-$400. Add $100 per unit for labor and you get an idea of cost. Not knowing the size of your lanai, it’s hard to determine a fair profit margin. 40-50% is the norm.

We just did ours and single pane was enough. Also just added the mini-split after 1 year. Waited to see if we really wanted/needed it. Answer is ‘yes’.

Cardinal glass company in Ocala the largest manufacture of windows in US

They make a solar glass #320 that is amazing, look them up online

I did mine with that 320 double glazed it was under $10 a sq ft for the glass without labor.
So any installer has a low cost supplier nearby

So about $3,000 for 3 walls of a 12x20 never needed AC left the sliders out.

So $18,000 is an outrageous rip off:ohdear:

Do not use aluminum frames they transmit heat & cold.

Wood or vinyl for frames is better.

Be sure they have ARC approval & building permits.

We ordered our double pain windows in October . Just got them installed March 1. I agree if I had known how long the wait would have been I would have waited. They have to take off the screens to rough in frames for measurements. Room virtually unusable. Love it now, custom windows did a great job. Like others going to wait to see about mini split but definitely getting it insulated.

The only way I would pay half up front for a custom product would be if they can guarantee delivery within 60 days, and I could use a credit card. If they didn't deliver, I would dispute the credit card charge. There is no logical reason that the contractor needs the money that far in advance. They may have a materials backlog, but the fabricator is not going to spend more than a few weeks to fabricate the windows.

We enclosed ours with dual pane. More for sound proofing than anything else. We didn't add a mini-split, but we did have insulation put in. That made a big difference. We leave our lanai doors open all day and that takes care of the temp.

We debated this question for a while and went with double pane for about the price you quoted (and insulated the ceiling). We are so very thankful that we chose double pane. If the doors are left open all the time, the temperature seldom deviates more than 3 degrees F from that of the house. It has made the lanai a four season room that we spend lots of time in. We viewed that we always have the option to add a mini-split, but I doubt now that we'll ever do that. Not that it was a big deal for us, but it also does a good job insulating against noise.

We had Windows of Central Florida do the work in late 2019, and were pleased with their quality and timeliness.

We have acrylic sliders in our lanai, solar shades and a mini-split ( a/c and heat). Love it and have had it for over 10 years. The lanai is East facing.

I would get a couple more quotes that's a TAD high keep ion mind you also have to add HVAC .

3 years ago we had double pane glass and solar shades installed on a southern exposure lanai...we have two ceiling fans in the lanai, one pushes down, the other draws up. We also have an 11 foot opening when the sliders are fully open. We haven't had the need for a split, the a/c unit in the house had plenty of capacity and there has been no noticeable increase in electricity.

Maybe three times now in the dead of winter we've used a small space heater in the morning just to take a slight chill off (at night we leave the sliders open, but draw the vertical shades, basically for privacy)

converting the lanai to a four season room, that no longer gets soaked when it rains was one of the best things that we did

I ordered my double pane windows in September, and they didn't come in until 4 months later. A lesson in patience, for sure. I currently have a 3 month wait going for them to remake the screen, which was wrong.

We had our lanai closed with 5 simonton perfextion platinum weries windows, 5 sliders double pane low 2, coil and siding under windows with foam insullation, door, deadbolt, insulate attic with R 38 above attic, plus I had to have a larger window installed in our master bedroom to meet requirements. I'm VERY happy and have just opened the sliders and not have had to add A/C (AM sun) We used Windows of Central Florida 352 217 8151. They were on time, great technical work, everything cleaned up each day. The inspector said "I never have a problem with them". Total cost including window was $13,995.00

Our lanai faces west/northwest. It is 16x28. We have single pain, tinted sliders by Custom Windows. No screens, as we open into our birdcage. Service was good. Cost about $9200 in 2017. Single pane is hurricane rated for a cat 1. Light enough to remove if we think we need to for higher winds but that is rare here, so far. Don’t think anything would withstand a cat 4 or 5, so I’d be interested in what category a salesman states a double pane would withstand. Stating “hurricane” protected is nowhere specific enough to substantiate the cost. We did do a Massey split Heat/ac Mitsubishi unit. Had the lanai ceiling insulated by Solar Guys & added electric roll down shades by Shade Bros. Good decisions all. Keeps house cool & clean. Added about 500 sq ft more of living space. By getting single pane it paid for the ac unit.

Good luck with your decision

The price I cannot comment on. We had double pane windows put into our previous home. It was up north and the extra insulation factor was important. Here insulation is also important. Insulation slows down the flow of heat. Here it will slow heat coming in
as opposed to heat loss.

The double pane windows we purchased were double thick glass so essentially 4x as thick. Due to the weight I assume part of the cost is hardware, framing etc to take the extra weight. Also, the windows we purchased had built in UV filtration. How effective that is, what it is worth in terms of value I don't know but our windows had a blueish tint to them. Not at all obvious from the inside looking out but it was obvious compared to neighbors windows.

The sound deadening is dramatic. Perhaps a major reason to do it. Our windows stood up to snowball, ball etc from DENNIS THE MENACE the brat next door.