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tekjunkie28 | Posted in Energy Efficiency and Durability on

I have a 21 year old Nordyne unit. It is a 10 or 12 SEER 3 Ton HP.  I will be down sizing to 2 Tons and am wondering if getting  a staged unit or an inverter unit is worth the cost over a standard single stage?   I currenly live in Roanoke Va and have a 1972 ranch style home and the Unit is located in a vented attic. I have no plans to foam in the attic but I have been actively air sealing conditioned space bit by bit. My home has no shade trees directly over it and faces East so it gets full sun on all sides excecpt the north side which gets sun VERY late in the day if at all.  My electric bills are averaged around $190 a month with a yearly consumption of electric KW ~22k or ~1750 per month.  A basic load calc comes in at 1.85 tons and right at 1.5 tons if I were to change my orginal windows for something newer such as double pane and add in a proper amount of attic insulation.

I have a finished basement but Im pretty set on adding in minisplit to heat and cool it. Im guessing around 9k BTU but even a 6k BTU maybe oversided.

I also am interested in burying my flex runs in the attic insulation. I have read up on it but I think they are too far from conditioned space and I think my area maybe slightly too humid but IDK. Need help on that also.

My #1 goal is to have a comfortable home but also lower my electric bill enough so I get a nice ROI in a few year or 10 at the most.

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  1. paul_wiedefeld | | #1

    The heat pump both heats and cools your house with no furnace?

    1. tekjunkie28 | | #3

      Yes. Currently I have just the 3 ton heating and cooling the main floor. 1 8" flex duct goes down thought a closet to the basement. It's cools the basement okay but absolutely useless for heating. The 3 ton has electric strip as assist. The basement has electric baseboard heat also but I try to only use that one the coldest days of the year.

      1. paul_wiedefeld | | #5

        I see. The variable speed system will be more comfortable. It'll also be better at dehumidification. The hard part is determining how much your resistance heat contributes: if you get a cold climate heat pump with sufficient capacity at low temps, your energy savings vs. resistance will be huge. As far as I know, there are no single speed cold climate heat pumps, which could make the question: cold climate vs. not, instead of inverter or single speed.

        1. tekjunkie28 | | #7

          I am not sure about the cost of resistance heat. I think my KW cost is somewhere between 11.4 and 12.2 cents per KW. I can tell you my KW usage in Jan and Feb are 2532 and 2415 respectively. Compare that to the almost constant KW usage from June - Sept of 1813, 1878, 1816, and 1782. Furthermore my KW usage during may of this year was 1074. That is the lowest my bill has ever been I believe. The current months bill (oct) is $144.95 at 1198 KW. I do know my HP is on a timed defrost and more then half the time it seems that there isnt any frost on the coil when it goes into defrost. I hope all this helps.

          I should also add in that this probably isnt our forever home. But we arent moving is less then 5 years i assume. Maybe not less then 10. The wife likes it here but I dont care to much for it. I have spent over $18,000 in electric since we moved in 7.7 years ago

          1. paul_wiedefeld | | #8

            1198 kWh in October! I'm a few hours further north and used 411 kWh with a 2 ton cold climate heat pump and a separate .75 ton minisplit. Roanoke has relatively mild heating design temps, so it'll be easy to find a heat pump with enough capacity for the house.

            As to 1 vs. >1 stage: having multiple stages is definitely more comfortable. If you have to oversize on the cooling side to get the heating load covered, having a lower stage is a benefit for cooling. Having gone through the process recently, single stage vs. variable speed heat pump quotes were ~$2k apart. I'm not sure what a 2 stage comes in at, maybe $1k more than single stage? You're in a position to significantly lower your bills

          2. tekjunkie28 | | #15

            @Brian. My home is abut ~1600 sqft. I need to get some serious measurments but the main floor should be ~1100 and the basement is about ~500-600. When we bought the home it was advertised at 1828 sqft or so but IDK if they were including the garage in that.

        2. tekjunkie28 | | #9

          411kw!???????????????????? HOW????????? I am all electric but I have a standard HW heater thats 50 gallons and 8 years old. I have all LED lighting. I also have 2 kids and a wife. But we have brand new washer and dryer, New stove and a semi new fridge. New fridge is about 4-5 years old but its a GE profile fridge that Energy star rated. I have a dishwasher thats energy star rated. I use eco mode (low heat) when we use the dryer. No one takes long showers and I use water saver shower heads. I must have some vampire power coming from something.

          1. brian_wiley | | #10

            How many square feet is your home? Just wondering if we're comparing apples to apples in terms of energy usage.

          2. paul_wiedefeld | | #12

            Ha good question. I'd have to guess the heat pump, I'm making no sacrifices. AC and space heating are the big users for climates like yours. House is 1900 sqft and >100 years old. The important point (not size, not age) is that my heat loss is probably comparable. It's definitely not 1/3rd yours.

            I don't have an electric water heater, but everything else is electric. I'd probably be at 600 kwh for October with an electric resistance water heater. Age of electric resistance water heaters shouldn't matter much efficiency wise. Electric stoves and dryers shouldn't be more or less efficient based on age unless you're talking induction cooktops and heat pump dryers.

      2. capecodhaus | | #16


        The biggest problem with your house is the air handler in located in the unconditioned attic (you said). The attic is the worst place to install the air handler on these ranches and two story homes from the early 20th century but that's what contractors did. Burying the attic ductwork in insulation will help but my belief is if the air handler is in the 120F attic all day during summer that is counter productive to efficiency and comfort.

        These brick homes mostly predate the introduction of forced air furnaces and retrofitting wasn't pretty or easy to do.

        The worst part, it seems in the region of SW Virginia, after poorly retrofitting older homes with forced air systems, contractors took to the same practice for decades in new construction sticking everything in the unconditioned attic. Bad move!

        Consider making the attic conditioned space. Or abandon your current equipment for a ductless install and insulate the attic floor.

        What I did instead. I moved into newer construction outside Roanoke, the air handler and duct work installed within the thermal boundary of the home. Low utility bills. We have a 3-ton 14 Seer single-stage heatpump on 2600 sq ft total conditioned space.

        1. tekjunkie28 | | #18

          Yea, I agree but I dont think moving the unit to the basement and running all new duct would be cost effective. I also am not sure foaming the attic will be cost effective. I cant even get a foaming company to spray more then R21. If they did then it would cost be almost the same as moving the unit to the basement with new duct.

          I know moving the stuff down into conditioned space is the way to go but I think it wouldnt be cost effective unless this my the last home I was going to own. I dont think it is but who know... that decision is up to the wife.

          How would I do minisplits? 1 head for the LR, Dining, and Kitchen and then 1 head in each bedroom? If i did that I would assume I would need 2 condensers. Then there is the fact that each attached head causes efficiency loss and then there seems to be a lot of comfort issues with minisplits. I have almost ZERO comfort issues now. The biggest issue I have currently is the 2 grilles in the living room blowing cold air down on the couches during the summer.

          I have a friend whose electrically usage should be a little less then mine but not a lot. His bills run him about $100 or less. Unit is in a closet but Ducts are in the attic.

          1. capecodhaus | | #20

            Sounds like you need a new hvac system, first most.

            The next homeowner will appreciate that you installed new equipment and you'll start saving some money month to month. Spending more on the highest efficiency hvac unit will make little difference over a basic newer system.

            If you're planning on remodeling the main floor, it may make sense to move the hvac system to the basement at the same time and make certain the ductwork is optimized at that time if you're savvy.

            Maybe do a "flash and batt" to condition the attic space versus r21 spray foam only. You may end up with a higher r value for less money. Using your own labor will help lower cost.

            Or, maybe build a conditioned room around the newly installed air handler in the attic and bury the ductwork as best you can in insulation if relocating the air handler downstairs is too costly.

            Do you have any single pane windows in your house? If so, any replacement style double pane vinyl windows will be an improvement. Beyond that point once again the cost doesn't give you reasonable roi.

            With all the variables of a given home, I can't tell you where to place the head units for a mini split/mutli-split system without a better understanding of the home.

            Perhaps a combination of mini splits, some or all replacement vinyl windows and cellulose/fiberglass attic floor insulation could be had for similar money to relocating the hvac to basement only. Get some quotes!

            Lastly, if a homeowner doesn't love their home, why over invest in it? Just keep it maintained and plan your exit strategy.

  2. walta100 | | #2

    Much like replacement windows it would be very rare case if you could show a ROI on the replacement of working HVAC equipment given how often most people move.

    Unless or until you need a repair costing more than $500 the low cost option is to keep using the unit you have.


    1. tekjunkie28 | | #4

      Even though that unit costs me quite a bit to run? Seems most are in agreement that at least changing out equipment would cut some cost on electric bill. I already has a $600 condenser fan motor replacement last year.

      1. paul_wiedefeld | | #6

        Keeping the incremental cost in mind is key: a 21 year old (or 1 month old) system won't last forever. A new system a year or two early isn't costing you much vs. waiting until it breaks.

  3. walta100 | | #11

    Let’s say half of the $190 was used for running the AC or $95 a month for 3 months in the summer and winter for a total of $570 and you changed the SEER from 12 to 17 would cut the bill by 30% or $171 a year and the new unit cost $7000 you would break even in 41 years if it could last that long.

    In my mind the math is different once the unit is broken and you must spend 5k to get another 12SEER or 2k more for the 17SEER.


    1. user-5946022 | | #14

      This. Just replacing it for efficiency or comfort will almost never have a decent ROI.

      But if you need a new system anyway the comparison is the incremental cost increase from the basic system to the staged or inverter unit. For that, you need to provide some info on the cost difference.

      I have a house south of yours in which about 5 years ago I replaced a 20 year old AC + gas furnace with a bare bones basic system. Went from a 3 ton to a 2 ton. Power bill immediately went down even in the winter probably due to new system being more efficient and being sized smaller. Power bill in summer is always under $100; HALF of what old system was because the old system was probably leaking or just really bad. I declined the $2k cost increase to go with two speed and/or higher SEER, etc. I would NEVER recover that cost. Even if the upgrades would have saved me 20%, that is $20 max in a month. Lets say the upgrades (multi stage, higher SEER, etc) would save max $120 year. Would have taken me over 16 years to recover the costs if that. Not worth it.

      For comfort, obsess over air leakage. I can't emphasize how much that impacts comfort. Seal everything. It has the added bonus of resulting in power savings as well...

      1. tekjunkie28 | | #17

        Dang. The only reason I am looking into 2 stage or multi stage systems if for any possible reduction in electrical costs. I guess im probably chasing pipe dreams. During cold snaps my electric bill has been upwards of $330 but that was just for 1 month. It does seem in my case that my summer electric bill is 50% for cooling or very very close.

        1. paul_wiedefeld | | #19

          The multi stage systems will be more comfortable and will save money. Some combination of these two might be worth $1-$2k, might not. You shouldn't be paying $330 a month with a new heat pump in your climate.

        2. d_barnes | | #21

          I think the big distinction regarding the comments is removing a unit in the middle of its service life, vs your 21 y/o oversized system, nearer the end of it’s life. There’s another comment agreeing with my approach. Don’t wait for an old unit to break down, and be pressured into a quick, possibly bad decision, instead keep doing some research, and replace it on your terms.
          I removed a 22 y/o furnace and 5 ton A/C, switching to a 3 ton Heat Pump, new R8 insulated flex duct with metal elbows and Wyes for low Static Pressure, reran on the floor of the attic I Air Sealed, then deep buried in R60 blow-in insulation.
          I went with a Rheem RP17 3 stage inverter compressor, 2 stage indoor fan, 18 SEER and rated for the full 3 tons of output at 17F.
          I think there’s a line between 2 stage units, then, lower cost Non-communicating inverter compressor units like that Rheem or my current Bosch ids 2 ton, then there’s the expensive fully modulating, fully communicating, more complicated units. Being a Heat Pump, and getting efficiency and comfort benefits year round, I would consider 2/3 stage or a Non communicating inverter.
          I’m in a Dry climate, you should check before deep burying your duct system. You can for sure run it low, above the insulation, rather than strapped near the roof deck that sometimes happens. There’s also a new roof deck insulation product from Knauf, called IRD, that more easily staples up, but does Not create a sealed attic, it only reduces attic temps and the load on the ducts and equipment in a vented attic. R19 roof deck batts is now code here, with equipment/ducts in vented attics.

  4. bigred | | #13

    With a 21 yo unit, you are on borrowed time. While waiting for a complete failure might save you some money vs replacing 1 year earlier, what about being able to get a company do to an install quickly when it fails (likely during the coldest or hottest part of the year) or being able to get the particular energy efficient unit you want without waiting. I know I would rather schedule and be without HVAC for one day rather than weeks, particularly in August in Texas.

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