Dear PoPville – Seperate HVAC for the Basement?

“Dear PoPville,

My husband and I own a rowhouse with a basement apartment, which we rent out. One issue we face is that the house only has one HVAC system, so the thermostat is in our section of the house. If our tenants are too hot (which happens a lot), they text us to turn up the AC. Because of this we miss out on opening our windows on perfect fall days.

We would like to create two separate HVAC systems, especially because we are planning to move out and rent out the entire house next year. Do any of your readers have experience with this and can let us know about how much it cost? Also, any contractor recommendations?”

28 Comment

  • I can’t comment on your specific situation, but can recommend contractors to avoid. J&P Heating and Air took me for a walk around the block to the tune of nearly $3k, and Olympic Aire tried collecting on a surprise bill (in the thousdands of dollars) that was bogous. Good luck, I hate vetting contractors.

  • We had Climate Heating and Air install our furnace. They also do the yearly maintenance on our AC units. I have been satisfied with them, but I have not had them install an AC unit or ductwork (and it sounds like you may need at least some to separate the two portions of the house).

  • You might want to look into a split system–that could be the cheapest and easiest way to do it. It involves no duct work, just a couple of fairly small holes through the exterior wall. Then each room gets a wall-mounted blower that can be turned on as needed–it’s sort of like having individual climate control for each room. You don’t have to turn on the AC to the whole place if only the bedroom is hot; just turn on the blower for the bedroom. I believe they’re a lot more efficient than central HVAC systems and are energy-saving as you only need to turn it on for the area that needs heating or cooling.

    • What you are referring to is a Ductless split system (a traditional split system has ductwork). You can find these online for ~$1500 but they would not have a warranty or any guarentee’s unless installed by a certified dealer or lisenced HVAC contractor. For a bigger name HVAC company to install one of these systems you are looking at probably around $4500-5000 to have it done right. They are just slightly less than a traditional split (excluding duct work price). These units are great for saving space, VERY quiet (you won’t even know when the indoor part is running except by feel), and can be made so that it can be expanded later on by adding additional indoor units. Mitsubishi is by far and away the standard bearer of ductless split systems. Otherwise to install a traditional split system (heat pump or AC/GF) w/ ductowrk you are going to be looking in the $13-20K range.

  • google split ductless AC units – you can setup as many zones as you’d like, often times running 4 zone systems off of one external AC box that sits outside the house. Pretty easy to install. I did my rowhouse myself, it didn’t take much more than a weekend to install a two zone system – one for each floor.

    • Just curious as to where you located the units inside the house. I like the idea of this but don’t so much like the idea of big plastic boxes sticking out of the wall.

      • LG has a system called Art Cool–you can customize the panels. I have no idea what they look like in real life, but it might be worth checking out.

  • Wouldn’t it be cheaper to install a second thermostat in the basement? Is that even doable? You would still have the sharing issue, but at least they wouldn’t need to contact you to make changes.

  • *Separate

  • Give PCK HVAC a call and have them come to give you some recommendations.

    Mirko from PCK is the most trustworty, amazing HCAC person I have found in DC. He really, really, really rocks. He just finished up $2k of fixing our crappy HVAC system and it was amazing.

    I called four other contractors (all the big companies) and none even bothered to return my calls or come look at the work to give me a bid. Mirko came after work hours, worked weekends (both days when necessary), worked hard and got the job done. Highly recommended.

  • I recommend Climate. They’ve been taking care of my furnace and air conditioning for nearly 20 years now and are very reliable. They are installing a new furnace for me next week and provided me with several options – and recommended that I take the lowest price one — very unusual and very consumer friendly.

  • Guys,

    The already have the ducting through the house so there is no utility to mini-splits or ductless ac. Reading comp is key.

    The solution is pretty simple. You have a single zone system, you need a two zone system. I would just go ahead and buy a new system with two zones and not try to use your existing system. It is way oversized for one zone.

    I’d go with a Trane, Carrier or Rheem brand. Don’t know the size of your rowhouse so can’t tie down a specific price but it should be in the 7-10K range depending on how efficient you go.

    • You cant just cut the ductwork in half and put a separate system on it. you would have to replace it all and design a new duct system/layout. You could try to just split it in half and put dampers or an automated zoning system in but still it would be limited due to only having 1 system at the moment. It also never would be close to efficient and you’de prob lose ~30% capacity. The best route is to close off the basement duct and put a ductless split in.

      Also how can you determine the one system they have is oversized for an area you are reccomending adding a 2nd zone for? Seems comprehension is perhaps key….

  • You can convert your single-zone system to a dual-zone using multiple thermostats and motorized dampers. Of course, you still run into the issue of splitting the bill… but this would accomplish the functionality you desire.

    For example, the thermostat controls the damper, and thus, the airflow to the area. If the AC is running and the basement is too warm, a temperature reduction on the basement thermostat will open the damper to the basement more, providing more cool air to the basement.

    • +1
      This is what we have for our English basement. A separate thermostat controls a motorized damper, which directs the airflow to upstairs, downstairs, or both. 1 HVAC system, 1 blower, 1 condenser, 2 zones, but 1 bill.

  • for the cheapest, most practical solution:
    you probably want to separate the basement and house ductwork (wall it off inside) and route the basement ducts to a new HVAC unit. assuming your basement is separately metered? your tenants do not want to share a utility bill, and if the existing unit works ok, you might as well get a few more years out of it.
    for frame of reference, we purchased a new unit recently(not sure the size, but electric heatpump/AC to cover 1000 sq ft) and installed it cost just over $3K.

  • Google Mini Split. These are cheaper and more than adequate for a basement apt. I bought one. They rock! Plus you can install them yourself!

  • A new high end heat pump system for my basement and first floor with new ductwork cost me $9,000. That was a complete install where nothing was before, but the basement was unfinished, so I wasn’t dealing with the cost of dry-wall repairs etc. My upstairs unit was a straight replacement for $7,000.

    I think your cost could vary a lot depending on how much effort it would take to separate your existing ductwork into two zones. If they really have to tear into the walls and reconfigure ductwork, that could drive the cost up really quickly.

    Those ductless units may be the best way to go for a basement, but as another poster mentioned, when you cut off the basement ducts from the existing system – one way or another – you’re going to have a system that may be overpowered for the upstairs zone.

  • I live in an english basement apartment where the temperature is controlled upstairs in the main house. My landlords but a window AC unit on a small side window right by the entrance to my apartment and also provide a space heater during the winter. I find this works very well because I can turn the AC on whenever I want, the unit isn’t making the house look ugly since it is on the side where no one usually walks, and it isn’t in one of the windows that provides significant light to my apartment. Would something like this work for you?

  • Zone control is the answer, as mentioned. I plan to do the same thing in my row house. I have a central HVAC system. Gets toasty in the summer on the top floor while frigid in the basement. For the short term, might simply want to adjust the vents. Make sure yours are closed and the tenants are wide open.

  • Keep in mind that the real reason that you should have 2 systems is not because the AC is too cold for you, but to prevent the spread of airborne bacteria and virus through the heating system, like bronchitis and TB. Shared ducts = shared diseases.

    • The “real reason” to split your HVAC is to avoid catching tuberculosis from your tenant?! Um, I don’t think so.

  • To the OP: I had the same issue and solved it by putting a mini-split system in the basement. As other comments have noted, it’s a ductless system and is a great solution for a basement unit.

    I did my research and decided to buy a Mitsubishi system online via goductless dot com. BEFORE I bought the unit, I made sure that I had a contractor lined up who could and would install the system. In my research I found that a lot of HVAC installers don’t work with these units and therefore the supply of those who do is very small. Some contractors will install a unit you buy online and others flat out won’t or will charge you a high price to do so. BTW, I decided to buy my own unit because I found that some installers were playing around with model numbers, compressors, and SEER rating … do some research and you’ll see what I mean.

    The installer I went with was Triple AAC Service (tripleaacservice dot com). Knew what they were doing and very reasonable in price. Good luck!

  • Install a split system in the basement and close off the AC duct work. A separate HVAC system will cost $$$.

  • DO NOT USE ARGENT! That being said I did this about 3 years ago to the tune of $12,000. I had a zone added to my 3rd floor and the installers were able to work in the attic. It may be more deooending on how the duct work can be utilized. You will typically need an additional compressor and air handler installed (they make combo units as weel).

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