Turning A Window Air Conditioning Unit Into Whole-House AC

Although air conditioning units are generally subdivided into a number of categories, including window, split and whole house/building units, they still work the same, with the compressor, condenser and expansion stages.

Extending the wiring for the AC unit’s controller board (Credit: HowToLou)

In the case of widely available window AC units you can indeed use them as designed in a window, or as [HowToLou] is in the process of demonstrating, as a whole-house AC unit. The main thing to keep an eye out for here is the rated capacity of the window AC unit (in British Thermal Units, square meters/feet). In this case [Lou] used a pretty beefy $600, 24,000 BTU window unit that should be good for about 1200 sqf (~111 m2) .

Most of the modifications are pretty straightforward, with the control board needing to have its wiring extended, as well as the AC unit’s air intake and exhaust on the indoors side. The unit is then placed outside on a stable foundation and inserted into a suitably sized hole in the side of the building, with the controller’s cable running to it from indoors. For the next step, [Lou] intends to connect the air channels on the AC unit to the house’s furnace ducts, to complete the whole-house AC installation.

Compared to a regular whole-house AC unit, this DIY approach has the advantage of anyone being able to just buy and install a window AC unit, whereas whole-house AC tends to require a licensed installer and a lot of additional costs. How well [Lou]’s DIY approach ends up working will hopefully be revealed in a Part 2.

108 thoughts on “Turning A Window Air Conditioning Unit Into Whole-House AC

      1. It absolutely is not. I am currently living in an apartment which is furnished with a single through-wall air conditioner in the living room. It does *not* adequately cool the bedrooms at the other end of the apartment. I’ve set up some fans to blow air from the living room toward the bedrooms, and all together the arrangement is keeping the bedrooms at a barely tolerable temperature, but it is no substitute for central air.

        1. This akin to the question : “How long is a piece of string ?” Meaning –> many possibilities.

          I have a 2.5 ton window unit. 1800 sf house in Texas. 5 years. Obviously area near unit 61°F, and areas furthest from 73°F.

          Insulated house, and failed home HVAC system, central air fan still in “ON” position. All good for me.

          1. At 1800 sf and using the central a/c to keep air moving, you seem to have a Great idea going, in the early mornings, I’d recommend turning down the temperature to allow the furnishings to help store cool for higher afternoons higher temperatures! Keeping rooms dark and venting attic helps too!

        2. Correct…my old apartment (now in a house before the housing craziness) had one of those “hotel ac units” and it was horrible….our 1 bedroom was on the “other side of the wall” so luckily they put a hole in the wall (and a grate lol) for a semi vent….ended up buying the biggest small (lol) fans I could find to find in the 🕳 to help pull the AC to that bedroom. Even set to 75 the bedroom was lucky to hit 78…..so at night we would drop the temp to like 72 to be comfortable.

        3. You dont have duct work in the house like OP did. Place the window unit in a window by a return and let the house fan circulate would be more efficient.

          Reading comprehension is important;.

          1. With your mastered reading comprehension did you notice that the original comment in this thread was not about using the ductwork of the house but “Install window AC in window, leave room door open.”?

        4. Yup. I had this exact problem in my last apartment. A window AC in the “office” would lead to the bedroom being uncomfortably warm even with fans moving air between rooms, and the “office” being extremely cold. Running the furnace in “fan only” mode didn’t help – in fact it seemed like it would allow heat to enter the ducts and would warm up the apartment.

          A window AC in the bedroom would lead to the “office” being sweltering and me not sleeping due to the noise.

          Had to put in a portable AC unit in the kitchen area (casement window, bleh), inefficient as hell but did an OK job when operating in tandem with a window unit at the other end of the apartment.

          1. Probably not enough total cooling power then. Cooling one room well and one room badly is a lot easier than cooling every room and all the ductwork. But all the other rooms except for the office and bedroom were probably more comfortable with the central vents blowing than otherwise. If not, the ductwork needs better insulation because it’s probably leaking a lot of heat the other way in the winter when the furnace is going.

  1. As an HVACR conntractor this is the stuff of my nightmares. Wrong in sooooooooo many ways. He already has a furnace so all he needs is an A-coil and plenum for the inside and the outdoor condensor unit. The unit looks to have a 120 volt USA plug on it so I doubt that it’s 24000 btu as stated in the article. The video and comments do not state the size of the unit. In the industry these are refered to as window shakers and are meant to cool one room not a whole shop. If I were to get a no cooling call and show up to see this the response is “We don’t work on those.” And your still getting charged for the service call. As a side note I did go to a garage sale one time and the lady had a shaker unit laying on the garage floor. The inside part (cold air) was pointed at her legs and the outside part (hot air) was pointed at the customers. It kept her cool although I thought it was a serious waste of energy.

    1. I worked at a place once that was in a historical brick building and the exec offices were inside the place as well as the shop, and they framed the offices in, and vented window rattlers into the shop. Nice for the execs, not so nice for everybody else…

    2. “the response is “We don’t work on those.” And your still getting charged for the service call”

      Typical d-bag hvac miscreant response.
      You wouldn’t get chit from me tough guy.
      oh, take that back – you would get chit… as in a big steaming pile on your truck,
      courtesy my cornhole.
      Take your attitude and crawl back under your rock.

        1. Reading the reddit groups for a lot of the “trades” (hvac, electric, construction, etc), plenty of those guys are more concerned about making a fast buck then quality workmanship. These are the same muppets that can’t be trusted to use a bathroom properly (ie. which is why a lot of job sites refuse to allow the “trades” to use customer facilities – case in point, building owner allowed hvac to use new bathrooms – didn’t take long – feces spread all over the floor, toilets stopped up with soda cans – freakin’ turd show !).

          And these same dimwits would charge a customer 100x more for a part you can get at the orange big box store – and put it in shoddily so it fails a week later…. smh…

          I have *zero* respect for these guys. I had to interview 5 contractors before I settled on the “right” guy (whose truck was spotless, tools and equipment in neat orderly spots, the guy knew what a “manual J”/heat loss calculation was – had the program on his laptop, knew what brazing vs soldering was…definitely a keeper). Unfortunately that guy was the exception, not the rule.

          1. This is why I do everything myself. I’ve hired no contractors, for anything, ever.
            Everything here works great and is well built, and I’ve gained a healthy savings account and a lot of knowledge for free.
            The internet has made this a doddle.

          2. The trades are _all_ a shit show in the USA.

            25% drunks, 25% tweaks, 25% stoners and 25% pill heads. Plus some multis.

            Hire stoner tradesmen directly and don’t lose the number once you find a good one. Never hire or patronize anyone with a religious symbol of any kind on their placards or signs (fish in particular means ‘am thief’).

            Also be aware that some trades are particularly unskilled. There is no reason to ever hire a ‘union painter’, just hire anybody, they will do a _better_ job.

            The tradesmen are only half the problem, the other half is the contractors. Try to avoid hiring one, at all.

            Buy your own supplies, if the tradesman doesn’t like that, show him the door. No money up front (buy supplies yourself, remember). Money only on completed milestones.

            There are tradesmen who will tell you ‘nobody will agree to those terms’. What they really mean to say is ‘nobody as crooked as me will agree to those terms’. Know you dodged a bullet when those thieves stomp out the door.

          1. Contraction of “you all”, which is perfectly proper. Used to clarify when you mean the plural when saying “you”. It’s the kind of word that gets added to any language that doesn’t make that distinction in the first place.

      1. As a former field guy, I gotta say I hate this attitude. My time, my knowledge and my experience is valuable, and if a customer calls me out, they are buying that. I always let them know that upfront, and they always have the option to say no, but the moment they pull the trigger and call me out, the customer is on the clock. If it’s something stupid, the customer is paying for a bit of education. And I’m not going to feel bad about that.

        1. You’re absolutely correct. Its the same as I am an auto technician by trade and everyone wants a dignosis of their vehicle issues most times without seeing it. This is as valuable as taking it for a free code scan at Auto Zone. I can give you a dozen hypothetical repairs but a proper diagnosis always helps. Had my secondary heat exchanger go bad on my furnace. Paid for them to confirm what I had assumed and replaced both primary and secondary myself for half the cost.

      2. Yeah change the complete design of a unit. So much so that it couldn’t even pass code and a contractor is supposedly to take the responsibility and liability to work on a unit thats design was changed without the manufacturers stamp of approval. Then get mad at contractors because they won’t work on it, or take the liability. Make sense to get mad at the contractor for telling you how it is! So many code violations here its pathetic and they shouldn’t charge you for wasting their time, laughable!

      3. So you expect someone to work for free?
        Ever hear of a service call fee? His gas, his time but you expect freebies for being ignorant?
        I’m a hvac technician and he’s absolutely correct. Service call fee is charged when we come to a home that has called us for service. No we don’t work on window shakers due to the fact it costs more to repair them than it does to replace them.
        So for the time and gas it takes to come out to a home, yes we get paid.
        I wouldn’t expect someone like you to understand this. As matter of fact, someone like you is who I tell to go to hell and freeze in winter and cook in summer. I have zero sympathy for entitled morons.

        1. Okay, here’s the thing about that: a technician has a responsibility to make a reasonable determination over the phone that a job is something he can do, before committing a customer to a service call. If a customer does not misrepresent what kind of equipment he needs work done on, and the technician cannot determine over the phone that this is not a job he is able and willing to do, it’s on HIM. And I’m speaking as a former service technician. If I advertise that I fix air conditioners, and don’t mention that I don’t do window units, and I don’t ask if this is a window unit, and I come to your house, guess what? I just wasted my time, not the customer’s money. Now, if the customer, who modified a window unit to cool a whole house, tells me that it’s a central A/C, and I show up and see THIS, yeah, he’s going to pay for my trip.

      4. Your inconsiderate. It costs a lot to put a truck and service man on the road. Not to mention insurance, etc! Should a serviceman or small business owner be a charity for every uneducated ac equipped so and so. ON THE OTHER HAND—-A few questions by whomever took the call in the furst place would have been appropriate.

      5. Yeah this is prolly not 24000 btu on 115v, but still the attitude is ridiculous. Hvac guys are leeches. They offer “tune ups” for $59, then find $1500 in “problems” and scare little old ladies into paying.

    3. But then you have to hack the unit itself, detaching the existing evaporator coil, and running long pipes between the external unit and new internal coil. So you need to drain the refrigerant, re-fill and re-pressure it, etc, etc – not the stuff of typical DIY.

      1. But obviously the actual problem is that regular customers can’t just buy and install themselves, split aircon units. Why do you need to be licensed? makes no sense.

        1. While working for a large HVAC manufacturer for almost a decade, I used to ask this question to the Engineering team frequently. Mostly because the cost you pay for an HVAC install is often orders of magnitude greater than the cost to manufacture the damn things. For the most part, it’s regulations that are keeping most consumers out of space. Maybe for good reason given theirs often huge electrical and gaseous risks involved, but that doesn’t mean some of that stuff couldn’t be abstracted away. Line sets are the first hurdle since they have to be connected between the cools and compressors. I used to recommend a system similar to quick connects in air compressors but a little more solid like you might find on a gas pump. The second hurdle came from the electrical requirements and my first thought was the turn lock styles for RVs and generators. Finally, there’s the ductwork both incoming and outgoing. Getting those initial boxes to fit various air handlers and furnaces is where the magic in metal working begins to shine. Branching off plenums is quickly diving into “certain level of expertise” needed to not waste a lot of energy and refrigerant. In the end, there are simply too many pieces that could have dire consequences of done incorrectly. Not that an amateur couldn’t do it, just that it’s unlikely to ever be as easy as buying a window unit from a box store and cracking the window enough to hold it up.

          1. In some US States homeowners can do all their own HVAC, plumbing, electrical, concrete, carpentry, drywall etc. on their own residence. Inspection requirements vary. In Idaho we can do all of that, major carpentry (like building a new addition or converting a garage to living space) requires a building permit and inspection. HVAC? If you are smart enough to figure out how to do it, go for it.

            I did my own mini split install. They’re easy since they all come with the refrigerant already in the outside unit. It’s not difficult to cut and flare the lines if you want the 16 or 25 foot standard lengths shorter. A vacuum pump and hoses+gauge can always be resold. Or if you don’t want to buy a vacuum pump and can live with dealing with two stock line lengths, get a Mr. Cool DIY or one of the others with sealed lines that don’t need vacuumed.

            If you can read and understand books and are smart enough to figure out the difference between YouTubers who know and don’t know what they’re doing, it’s not difficult to learn how to build or repair anything in a house.

            In my case it helps that I grew up in three homes my father did major work/rebuilding on, and I helped on the 2nd and 3rd. I was also deeply involved in auto mechanics from the day I could identify and hand my father tools.

            People ask me how I can know so much and am able to do such a wide variety of things. #1. I read a lot about a lot. #2. Life experience. #3. The ability to apply #1. to #2. #4. I watch other people screw up *then I don’t do what they did*.

        2. Because it’s a skilled trade, and in my opinion while probably a little bias is the most skilled trade, a good HVAC tech knows electricity, refrigerant, plumbing, air, and metal. Sure anyone can put in a unit, but was it done right? Ductless units put in by homeowners rarely make it past 5 years without an issue. Cause they use a harbor freight flaring tool. and don’t use a torque wrench.

          1. I would argue under water welding is more skilled. Also fields that have to provide a finished outcome. Havac, plumbing, electrical, all are wamb bamb fields. No one looks at it when you are done. Try coating 1000 sqft without a flaw or hair in the product. Sweating pipes are child’s play in comparison.
            I think ultimately we should have respect for all ideas. People should be able to do things without the okay of the government or hvac association.
            You can charge for the work you do.. why be so arrogant to turn someone away if they have cash?
            Like so you can do another job that is easier?
            That’s not how I treat my clients.

        3. You can, at least here in the US. I helped a friend do his own install a few years back, we installed all the units and piping and wiring up to the electrical box. He had to pull permits and get a licensed electrician to do the wiring, and an HVAC guy to come out and charge the refrigerant, but that ended up being a $$$ pricetag instead of $$$$$ for having it all done by a contractor.

    4. Just because HVAC guys charge like they are God’s gift to this planet. And because they are more arrogant than a Hardwood floor guy (my self).

      I give this 5 stars. 😄
      I will say that if you are spending 600 on a window unit.. might as well she’ll out 1500 for an actual hvac condenser with the fan and the grill large enough for an entire house.
      I did recebtly find out that too powerful a unit won’t remove the humidity from the house because it cools too fast.

      Also side note. Someone did this idea for a one room location insulated with foam and made a walk in freezer. That you can do with a WIndow ac unit and a separate temp gage.

  2. “24000 BTU” is a quantity of heat energy. As an indication of cooling power the number is meaningless without an indication of over how long that energy is pumped. The assumption might be per hour, or 24 kBTU/h, equaling 7 kilowatts of cooling power, pretty optimistic from a window unit. In Arcane Freedom Units that’s 2 tons (of ice melting per day).

    1. Buying an A/C unit, or A/C service, or A/C parts is not the same as a Thermodynamics course discussion at university. One does not buy an evaporator (coil) for a “36 000 BTU per hour” unit.
      In conversation re A/C capacity (verbal and print), “…per hour” is always assumed. Anything else would be considered ‘stilted’, and a sign of one’s almost complete lack of experience concerning things A/C.
      Total agreement with @mayhem (above).
      Being a hacker is nice; can–maybe–save you some money (time is a very questionable, whole ‘nother matter); but be aware that, unless the tradesman is a friend, you won’t get one to perform any service on your ‘hack’. You wouldn’t be able to afford the repair…

      1. AMEN! I wouldn’t touch it. It would cost you more to have me fix it, then you paid for the whole thing. The DIY stuff in this trade is NO GOOD dont DO IT! Improper refrigeration practices lead to poor efficiency and premature failure. Hire a professional.

        1. OOPs! I claim brain cramp.. Paul, you are correct of course, sorry
          Tons of cooling is archaic but to me it only reflects that at the time of development and up till my fathers generation most people that had refrigeration were still sawing ice of the winter frozen lakes for their ice house or getting the same delivered to their ice box. Maybe not as obscure these days as hogshead or stone but I would suggest “freedom units” to me are more like “the size of 10 olympic swimming pools” or an asteroid the width of 200 chickens” as I saw recently in a headline making fun of “freedom units”.
          Tons are slowly going away as are horsepower and BTU (also obscure to many) – where previously given with metric equiv in parentheses but now commonly the other way around, but it will be awhile in the US probably.

        2. Excuse please. 1 ton of AC is 12000 BTU. That’s what is required to keep 1 tonne of ice from melting in an uninsulated old shack out by ye old lake when it is 80 degrees out and the shack is in the shade of the old oak tree with a hundred yellow ribbons on it.

    2. What kinda doodoo are you trying to say here? First two sentences are #duhhh and you don’t believe a 24k btu window unit produces 24k btu? Are you from Somewhere they stick a label to it no matter what btu it is ?? A 24,000 BTU air conditioner will use more or less energy depending on its seer rating…And lastly, yes it’s 24,000 BTU a second, a minute, an hour, a day, a week,.. thanks for your brilliant dedication to clarity.

  3. Well, this is certainly a hack, no doubt about that. Whether it is a good one or in any way recommendable is certainly open to question. At some level you do what you gotta do I guess.

    1. Definitely a hack. The fan on that window unit will not overcome the static pressure of the ductwork for the entire house. The thing will provide lousy cooling… at best

  4. <>
    You’re moving heat, not creating it. An AC is a one way heat pump.
    Another archaic term is Coefficient of Performance (COP) which is the amount of heat moved divided by energy used. You can expect a COP of three or so, meaning you can move 3 BTU of energy for every BTU of energy consumed by the compressor. A Freedom rule of thumb: it takes about a hp per ton of cooling (12,000BTU/hr). Or 2 hp for this setup.

    1. Oh god why don’t people just use sensible measures. BTU, tons, horsepower…
      Just use kilowatt of input power resulting kilowatt of cooling power to get to the COP.
      Mechanical kilowatts if you wanna drive the whole thing with an internal combustion engine.

      1. At least the dimensions are simple for those alternate units, and besides it’s easy enough to have a computer handle the conversion without needing to look at conversion factors.

        I could give you my car’s fuel economy as being around one zettabarn, which is a perfectly decent metric unit, and it would be unambiguously correct. But fuel economy measurements are conventionally expressed by relating a volume to a distance, rather than canceling out and giving you an area. Wouldn’t you rather mpg in that case?

    1. Yup. If you have access to attic space there are ones with “ceiling casettes”. Mr. Cool recently introduced a DIY version of those, for people who don’t want the inside unit on a wall, or who don;t have a good place for a wall mounted one.

      The gocha there is whether or nor one lives in a US State (or other place) that allows a homeowner to do their own HVAC work on their residence.

    2. Yep, supposed to be pre-charged with quick connectors for the hoses. And they’re often also heat pumps, unlike many window units. It should be much easier to find a hvac person willing to do the final hookup for a nominal fee if your jurisdiction doesn’t allow you to do it yourself, versus a regular aircon or this contraption.

        1. Eh, lots of places you can get a refill and repair done under that. There’s got to be somebody who’s gotten certified who’d like to make a quick buck inspecting and flipping the switch on a ready to go unit.

  5. Unless he’s going to install a relay to turn on the furnace fan, and another to close a set of bypass dampers, this thing is going to ice up it’s evaporator coil in the first hour. The fan in it can’t develop enough pressure to force air through ductwork.

  6. I can see something like this for a small shop or garage where the windows are high ( hence moving the thermostat if it didn’t come with a remote ) and you wanted the air to go to certain spaces , but anything larger than that …. not a good idea , … But still a hack !

  7. HVAC Contractor as well. Looks to me like more work then needs be. If you can’t afford a whole house AC. Would be easier just to go get few more window shakers. We give out loner window units when we have a timely job. Amazing how 2 or 3 window unit do a great job. While we’re installing a several thousand dollar job! Just hoping customer doesn’t figure that out! 😆.

    1. Yep when moms central ac went out that’s what she did….just got window shakers (a couple midea u shape ones which I’ve been told as efficient as a mini split)

      The app just turns them up and down as she moves around the house

  8. I just bought a mini split on sale for $499.00. A window unit of the same size from the same company was $429.00. It took my wife and I just 7 hours to install and it looks great. It even has WiFi connectivity. Why hack a window unit?

    1. The window unit would cool worse and use more electricity than the mini split. I replaced a window AC that was installed where a transom windows was over a door. Covered the hole with plywood on both sides and filled the space with fiberglass insulation. Mounted the mini split inside unit on the inside plywood. The place stays cool AND my electric bill has been lower than last summer with the window AC that ran constantly yet couldn’t keep it cool in here.

    1. Only where the air is dry enough to ensure enough water evaporation, and where freezing isn’t usually a problem. They work great in Tucson but probably not in NY or Mobile, St Louis, or Burmingham where many days are hot and 100% humidity. What cooling you do get in higher humidity areas is also often saturated with moisture making it “clammy”, so now you get to run a dehumidifier…

    2. Swamp coolers aren’t great in most of the places that need cooling. There’s a fine line between having too little water around to afford to spray it into the air, and having too much around so that raising the dew point is unacceptable. In the dryest places, you might emit heat at night and use a lot of thermal mass and insulation and shade in the day to mitigate things. In the wettest places, you might be able to use the water as a heatsink at least – but only if it’s at a cool enough temperature. In the middle, vapor-compression just works where swamp coolers provide little relief if any.

  9. So basically what you are saying is if you don’t want to put it through the window you can buy extra stuff add 8 hrs of work and put it through the wall instead and have the exact same BTU cooling capacity!! Genius
    Show me how to put an outside 2.5 ton unit in my window of my 600 square foot apartment and then you got something going on …

    1. Its not that difficult, they make some “split” units where you actually shut the vertical sliding window down and the unit is half in and half out with a small part at the bottom passing the refrigerant and some power and control wires.

      If you had a small mini split and a board to set it on, then passed the wiring and lines through yourself you’d have almost the same thing.

  10. AC windows units suck too much power and rack up your electrical bill. I had one b4 and compared it to my mini split consumption wise. A mini split would be your best way, with your same concept your doing suggest with a mini split inverter type. 2 ton or 3ton depending on your total sq ft. With WiFi can you can also use a Cassette type of air way they sell for compact areas.

  11. I am cringing at the thumbnail for the video. It shows a wall/window AC unit on the left and then the outside condenser/compressor from a split unit. What he is making is actually a ducted pad mount unit.

    1. That wouldn’t work. The blower motor on a window unit isn’t strong enough to overcome the static pressure of the house’s ductwork. The evap coil would freeze as a result and no cooling for the house

  12. It’s not going to work. Especially in a hot humid climate. I’ve been in HVAC for 30 years. An air conditioner does not make cold air. It removes the heat and humidity from the air. You just can’t simply blow air into a room through a duct. You have to also remove the air from the room in order to remove the heat and humidity. This is done through the return intake where the filter is. If you didn’t leave the doors open to all the rooms it’s not going to work because the blower motor simply isn’t strong enough to push the amount of cfm’s needed to each room and it’s not strong enough to remove enough air from those rooms. Especially those furthest from the return. Air conditioning isn’t a one size fits all when it comes to individual ducts in each room either. Some rooms require larger ducts or multiple ducts and others will require smaller ducts and each requiring different amounts of cfm’s will will change when you modify the plenum needed to come off the air conditioner in order to transition to your existing ductwork. You’re going to end up choking down an already inadequate blower. So don’t waste your time and money. Call a pro and have them repair the existing HVAC system that was designed for the home.

    1. This is a true professional comment. Whether home or auto air conditioning, refrigerator or freezer, they all work the same. None of these things make cold air. In all cases the heat from the area to be cooled must be passed through the evaporater, or A coil in a central air unit, where the heat is absorbed by the refrigerant and then transferred to the condenser to be released. It’s all about removing heat so if you think about it that way, we need to pass as much heat through the evaporater as possible to remove the heat from the area that needs to be cooled. We aren’t distributing cool air, we are transferring heat.

  13. Since this is, hmmmmm 🤔RIDICULOUS. I’ll be happy I have money, own my home, have money, did I say I have enough money? I can run my central HVAC like a normal human being, and stay cool. No BS hacks needed to stay cool in eastern NC…

  14. There is one problem with connecting ANY A/C unit in parallel with existing furnace duct is that air will flow in the reverse direction through the furnace as well as in the normal direction through the duct. This means less air flow through the house.

  15. Umm, yeah no the modifications to this unit , and how it’s installed, would, legally, require a license just as much as purchasing or working on or installing normal whole home AC components.

    Please don’t make misleading/wrong legal claims.

    Also, “lot of additional costs” uh yeah, those seem present here too. At least it’s normal bad info, and not bad legal info?

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