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Air Conditioning Load on Glassed in Lanai
We recently had our ~300 sq ft. south-facing lanai enclosed with single pain / non-insulated glass on our ~1900 sq ft home. The wife wants "open living" (i.e. to keep the doors to the lanai open) and thought we could do it after we blew insultation into the lanai.
I'm concerned that not only are the new windows and door not double-paned (i.e. no insultation) but also the added space will strain our AC unit In fact, when I saw the price of a mini-split I figured we might be able to extend the existing ductwork into the lanai after insulating, but I was told from multiple contractors that this would strain the AC and is not to code. Questions: even if we blew insultation, how much cool air would we be bleeding from the single-pain glass? With this leakage and new 300 sq feet to cool, how much of a load/strain would leaving the doors to the lanai open place on our AC unit and is that comparable to having the ducts directly into it? My idea of "open living" is not keeping the doors open, but rather using the lanai occasionally with the doors open (i.e. air conditioning from the home) but mostly using it later at night with windows open for a breeze to naturally cool it, but I supposed we're going to have to minimally both blow insulation and get a mini-split if my wife wants to keep the doors open all the time, correct? |
You definitely need to add insulation to the ceiling, as much as possible. Attaching ductwork to the existing HVAC system is not a good idea, and it most likely would violate the building code. Some contractors won't even do it. Adding a mini-split system is a good option but, I would first try leaving the doors open to the lanai and see how comfortable it makes the lanai. If you don't have a ceiling fan in the lanai, you should install one to circulate the conditioned air. If the lanai is mostly glass, single pane was not a good idea. You may also encounter condensation on the inside of the glass in the winter. A rule of thumb is that, in a typical house, you lose about two-thirds of energy through the roof, and about one-third through the windows. If the lanai is mostly single pane glass, you are losing even more energy through the windows.
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I cannot answer your question, but I can provide some advice. We also enclosed our lanai, and went to add AC. I ended up contacting an Engineering company to produce a ~20 page report for the county at a cost of $250. The report gave me the exact size of the AC required, however, I came up with the exact same number when i was researching mini-split systems, several of the sites have a way to fill in the room info to get the size requirements. As to whether this will strain your existing system I have no idea. I am going to send you a PM also.
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Easy solution for a fraction of the price. Go to Amazon and buy one of the BLACK+DECKER 8,000 BTU Portable Air Conditioner for Rooms up to 350 Sq. with Remote Control, White
Visit the BLACK+DECKER Store 4.1 4.1 out of 5 stars 49,772 ratings for less than $400. Problem solved when extra cooling is needed. |
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I took that to mean no portable units. But maybe my interpretation is wrong. Not that that matters, as it would be inconspicuous. |
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Week 2 The crew brought a 10,000btu portable for our bedroom, vented through window with a special kit. Bedroom was 14x18, closing both doors running 24/7. Inside temp of house around 84 at night. Bedroom temp 79 Some nights it was cooler sleeping in the screened lanai with a breeze, than the portable ac in the bedroom. Running portable AC for 3 weeks 1 day, Our Seco billing was $161 more than our July bill with a functioning AC. Bedroom faced south east. It was a long 5 weeks |
We enclosed our lanai years ago and when we did, we were told if we added AC or Heat it would be considered another room, increasing the tax.
I don't know how your house is structured, but our lanai was built under our roof line, so it was already insulted, plus there was already a fan in place. Now our lanai faces west, and we have two sets of sliding doors the one we added to enclose the lanai and the one that came with the house leading to the lanai. When we are not using the space, the double doors add insulation and when we are going to use the space, we just open the sliding doors to the house, and the lanai temperature with the fan quickly becomes the same as the rest of the house. |
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We glasses in our lanai, 400 sq ft. BUT IT faces north
The sliding door is open all the time. 2 ceiling fans, we tried the stand alone air for a while and finally put in a split, the problem with it is it drips if we try to get it to cool to match. We also put in the honeycomb shades which do help. Good luck. |
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We expanded our lanai from 180 to 320 sqft. Enclosed the lanai and added a 12K BTU mini split. The AC in the house died at the hottest time of the summer. If it weren't for the min-split, we would have moved to a hotel. With a couple of fans, it supported cooling the central area of the house. The contractor added one of the stand-alone AC units for our bedroom, and we survived the 5-week period to get the AC fixed. If it weren't for the mini split, we would have been in dire straits. Having the completely separate AC unit was a godsend.
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Somewhat unrelated, but 5 weeks for 2 of you to get AC fixed?!!! I hope you looked around for better service. If so, then that timespan is really unsettling. There's always something that can be fixed via readily available parts. Maybe you were convinced by them you had to replace the whole system. Mine has been completely refurbished, one part at a time as they failed.
My glassed in lanai is open to the house and has AC running to it. Even with double paned windows, I usually have to run a fan to feel cool in there. If you want to avoid various extra costs, I would just have fans to cool you off in there and keep it closed off to the house if your wife can stand it! |
Do yourself a favor. Insulate and put in the mini-split you won't regret it. We've tried all the other options, 1. leave the slider open, place a fan in the doorway (still too hot) 2. portable ac (still too hot).
Mini-split, roll down shades and insulation is the way to go. We used Sun Kool, but Munn's is a good option as well. |
Our lanai is 12x15, under the roofline, and faces east, so we get the morning sun. When we glassed it in, we researched cooling options. Of course the HVAC people tried to talk us into a split for $5,000. We asked about tapping into the existing ductwork and were given the song and dance about inadequate insulation and code violation. We insisted that they double check. They ended up doing exactly what we wanted. They tapped off our existing AC, blew extra insulation into the lanai attic, and we now have a comfortable room we use 365 days a year. The total cost for everything was $850. That was pre-Covid about 8 years ago, so things may have changed by now, but you should definitely push back on your HVAC company. You don’t ask, you don’t get.
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We just added a glassed in Cat 5 room to our west-facing lanai - about 220 square feet. Our situation is different though as it's insulated, low E, Argon glass. We raised the floor, removed the existing sliders and insulated the attic. We thought we'd need a mini split (around $6,500) but were able to get by with adding duct work to our existing 2.5 ton AC unit (around $1,800). Our room was finished a couple of days before we left for the summer but we monitor it (and other rooms) with ecobee Smart Sensors - the lanai's temp is the same as the rest of the house.
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Ac load for lani
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Also if you open the sliders to the house put the fans in the lani in winter mode so they pull air instead of pushing the air down |
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Some misinformation here:
1) you can install a mini split without increasing your property taxes 1 cent. 2) you don’t need a huge report done if you do the lanai correctly: double pane insulated glass, insulation in the attic and good solar reducing blinds. We built out our 33 x 12’ lanai using double pane egas windows, raised flooring, used the same tile as the house, electricity in the floors and columns, 97% solar blocking shades, and insulated attic. Our sliders give us 16’ of opening into the lanai so leaving the sliders open, we tried living for 1 year without a mini split and it got to uncomfortable out there, we use it every day. So we put in a Mitsubishi mini split but they call it a dehumidifier so we aren’t taxed. We got the more expensive unit that installed in the ceiling so you don’t see that huge box ($1000 more but worth it). We also use the Cielo thermostat (threw away the remote) so I can program the heating and cooling cycles similar to the ecobee. Being perfectly comfortable out there in any weather conditions, our electric bill has gone down because the mini split relieves the main hvac system from working overtime to heat/cool the increase of 350 sq feet. When we got bids from multiple hvac people, they quoted us units that would heat/cool the additional sq ft. I also got bids to use our existing hvac to pipe vents into the lanai. Every vendor said that would overwork the existing unit because all of our hvac units in the villages are under sized so they get rid of the humidity. I looked at zoning with a new hvac system which was more expensive than a mini split. There are 5 rules that the county has to see if you will pay taxes on your build. For me to get taxed, I would old have to take out my sliders. Since mine open up completely, I’m going to leave them there. I kept 3 boxes of tile so if I decide to remove the sliders, I have tile to replace the tracks. |
Open Living
I live in a patio villa and have an enclosed lanai and for 21 years I have left my living room door open so the air can get into the lanai. It gave me another room for living space without getting a splitter and my A/C lasted 21 years with no problems. Chuck Farrell serviced my A/C and there was never a problem.
I'm concerned that not only are the new windows and door not double-paned (i.e. no insultation) but also the added space will strain our AC unit In fact, when I saw the price of a mini-split I figured we might be able to extend the existing ductwork into the lanai after insulating, but I was told from multiple contractors that this would strain the AC and is not to code. Questions: even if we blew insultation, how much cool air would we be bleeding from the single-pain glass? With this leakage and new 300 sq feet to cool, how much of a load/strain would leaving the doors to the lanai open place on our AC unit and is that comparable to having the ducts directly into it? My idea of "open living" is not keeping the doors open, but rather using the lanai occasionally with the doors open (i.e. air conditioning from the home) but mostly using it later at night with windows open for a breeze to naturally cool it, but I supposed we're going to have to minimally both blow insulation and get a mini-split if my wife wants to keep the doors open all the time, correct?[/QUOTE] |
I would agree that most HVAC systems "may" be a little undersized here in the Villages so they run a little longer to help manage the humidity. But, in reality, HVAC systems that are your main home system usually come in 2, 2.5, 3, 3.5, 4 and 5 ton units so depending on the size of your home and the amount of insulation and the quality of the windows and doors in your lanai you may or may not have extra capacity to extend the existing ducts to the lanai. This is why some people say it works and others, not. The mini-splits many install for their lanai are variable speed inverter systems which are why they are so efficient. They are the best in managing the humidity. You can also get this technology for your home main unit as well.
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We insulated our glassed in lanai and insulated it. Best thing we ever did. Keep the sliders open all the time.
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Thanks for all the helpful information - especially the consideration of having the mini-split as a backup AC (although as we're in a brand new home, I'm hoping we won't ever need that)!
Here's a shocker (well, maybe not considering what I have experience thus far with TV construction): Our home just under 2000 square feet and our Carrier HVAC is only 3 ton. I'm no HVAC expert - which is why I posted on here in the first place - but I checked with ChatGPT and even without adding another 300 square feet of space to cool in our lanai, our brand new home has a significantly undersized HVAC. Here's the details: Our HVAC is a Carrier, Model/Catalog Number: 27SPA636A003. Using ChatGPT, I learned that "27SPA6" = Series and type of unit (in this case, part of Carrier's Performance series) and the next "36" is the key number to determining size. It indicates the BTU rating and "36" typically refers to 36,000 BTUs. If 12,000 BTUs = 1 ton, 36,000 BTUs = 3 tons. So we have a 3 ton system. Following up, ChatGPT offered: "✅ Conclusion: Your Carrier 3-ton unit (27SPA636A003) should adequately cool a home between 1,200 and 1,500 square feet in ZIP 34762, assuming: -Standard 8-foot ceilings -Moderate insulation and window exposure -No major heat loads (e.g., sunroom or uninsulated attic) If your home is larger than 1,500 sq ft, this unit may: -Struggle to maintain target temperatures on hot days -Run continuously, increasing your electric bill -Fail to adequately dehumidify Let me know your exact square footage and house characteristics if you'd like a more tailored answer." I replied that our square footage is 1967 square feet and we are considering adding a sun room (currently without cooling) which would be ~300 more square feet. ChatGPT said: "Thanks — that's very helpful. 📏 Total Space to Potentially Cool: Existing home: 1,967 sq ft Planned sunroom: +300 sq ft Total = ~2,267 sq ft 📍 Location: ZIP 34762 (Okahumpka, FL – hot & humid) 🔍 Analysis: Using Florida’s typical sizing of 400–500 sq ft per ton, here's the breakdown: Cooling Load Estimate Tons Needed 2,267 ÷ 500 = ~4.5 tons 2,267 ÷ 450 = ~5 tons (more conservative) Your current 3-ton unit (Carrier 27SPA636A003) is significantly undersized for this total area, especially with the sunroom added. 🔧 Recommendation: Option Use Case 5-ton unit Ideal for full-home + sunroom cooling in a Florida climate. Dual-zone system (e.g. 3-ton + mini-split for sunroom) If replacing the main unit isn’t ideal. Helps avoid oversizing the main system and improves efficiency. 4-ton unit (only if you don’t cool sunroom) Bare minimum for 1,967 sq ft, but borderline in FL. May underperform during peak heat. ✅ Final Answer: You should upgrade to a 5-ton HVAC system (or add a mini-split to cool the sunroom separately) to adequately and efficiently cool a 2,267 sq ft home in Florida. A 3-ton system will not keep up, especially in July–August, and will wear out faster from overwork. Let me know if you’d like help comparing Carrier 5-ton systems or mini-split options for the sunroom." Can any HVAC experts add color here? Are TV 3 ton HVACs undersized for Florida's hot humid climates? |
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>>>>>>>>>>>>>>>>>>>> How many BTU per square foot? A BTU, or British Thermal Unit, is a rating that measures the energy your AC uses in one hour to remove heat from your indoor air. The BTU of your HVAC system should be based on the square footage of your home, insulation quality, climate zone, and ductwork. Generally, you need 20 BTU for every square foot of space in your home. The chart below can guide your BTU choice: Home Square Footage BTU (British Thermal Unit) Tonnage 600 – 1,000 18,000 1.5 1,000 – 1,300 24,000 2 1,300 – 1,600 30,000 2.5 1,600 – 1,900 36,000 3 1,900 – 2,200 42,000 3.5 2,200 – 2,600 48,000 4 2,600 – 3,200 60,000 5 The larger your home, the higher BTU you’ll need to support your comfort. One of the most accurate ways to measure the right size AC for your home is with a Manual J calculation. So you AC is sized correctly. |
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That stated, I went to the site you referenced and it seems the year of construction (2025) is weighs more heavily than our post code (34762) so it does indeed recommend a 3 ton. |
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Have an Eastern exposure with only sun hitting it until 11 am. A mini split is essential IMHO. You will use the lanai every day with a mini split. |
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We have had two houses and enclosed both. Single pane. Don’t get sucked into double pain unless you have a west facing lanai with unobstructed view. We put insulation in the first house with 280 sq ft lanai. In second home we did not with 500 sq ft. Hardly noticed a difference. We put two mini splits in second lanai. We love it. One thing that is nice the villages weather and temp from late Oct to middle of April is great. Mini splits use was minimal. We use our lanai all the time. It’s well worth the cost to enclose and pit mini splits in. Ask contractor to put in the flush ceiling mounted mini.
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It might be less expensive and less trouble to just replace the wife?
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Being south facing you are also going to need to add rolling shades on all the windows that help block the sun to help keep it cooler. Everyone I know has the split units to keep it cool. The last thing you want to do is put a strain on your house system.
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