Life expectancy of old A/C

Discussion in 'HVAC Heating & Cooling' started by Nathan Davis, Feb 9, 2019.

  1. Nathan Davis

    Nathan Davis Member

    Joined:
    Feb 22, 2018
    Location:
    Springfield, Missouri
    I live in Springfield MO, and have a Rheem 5-ton central A/C. The system was first installed in 1994, but the compressor was replaced in August of 2005. I use the system for A/C only, not as a heat pump for the remainder of the year (The system is a heat pump, but it is wired only for cooling, and I have a hot water radiator system for heat). So far, the system has worked almost maintenance free. But I'm beginning to wonder if I should preemptively replace the A/C system before it breaks down in the middle of the hottest day--it will be 14 years old this summer. However, it is only used for about 4 months out of the year. So I'm also wondering if it still has plenty of life remaining because it's on for only 4 months out of the year.
    What do you think?
     
  2. WorthFlorida

    WorthFlorida ?

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    If it is a R22 system, most likely it is, ditch it. By 2020 no additional R22 is allowed to be imported into the USA. R22 now cost about five-six times more than R410a refrigerant used by most AC manufactures since 2012. Your old system maybe a SEER 10 at best, today SEER 14 is the minimum but for a few dollars more SEER 16 is reasonably priced. Also, 5 ton is way over board. When your unit was installed most figured 1 ton of cooling for every 500 sq ft of conditioned space. With today's efficient AC units a off the cuff sizing is not practical. It'd be well worth the expense to have a heat pump system sized correctly and installed.

    Depending on your furnace fuel type, it may be less costly to use the heat pump for heating and the furnace for aux heating. The thermostat can be programmed to use the furnace only, heat pump only, or both.

    Right now it would be a good time to get a good price for AC/heat pump in the middle of winter. If you wait until the weather gets hot, demand goes up and so does price.
     
    Last edited: Feb 9, 2019
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  4. Nathan Davis

    Nathan Davis Member

    Joined:
    Feb 22, 2018
    Location:
    Springfield, Missouri
    OK. That's what I figured but I wanted a second opinion. So I need to go shopping.
    We have 4300 sq ft plus a basement, but the basement does not need cooling. But 4300 sq ft works out to over 800 sq ft/ton. I have lots of insulation in the roof, but my walls are 6" clay tile with veneer, so they are a huge heat loss in the winter and the opposite in the summer. It gets a little uncomfortable in the worst of summer, so I'd welcome a system that does better. I've been think of adding a split system in the kitchen, but from what you say I may be able to get away with just using a more efficient system.
    Thanks for your insights.
     
  5. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    A full-on replacement of an R22 system is going to require all new refrigierant lines and air handler- it won't be cheap. I might be more financially rational to just recommission it once every 4-5 years by having it thoroughly checked out, including duct leakage, full static pressure tests across the system, refrigerant levels, etc., all the while keeping a "Plan-B" in your back pocket for what the replacement system(s) would be.

    IIRC this is a 3-story + basement nearly uninsulated masonry building. It's probably zoned by floor(?), and the sun-drenched upper floor probably has a 1% design load considerably higher than the rest. May houses like this would do pretty well with a mini-split heat pump (ducted or ductless, depending) per floor, each sized for their load. While that would be more expensive than replacing it with another 1-2 stage split system, it's usually cheaper than a fully modulating split system (Carrier Infinity Greenspeed, etc) , and considerably more efficient, more than twice as efficient as your current system, and nearly dead-silent.

    At MO type utility rates a standard split system heat pump isn't going to be cheaper than the natural gas boiler for many weeks out of the year, but a modulating mini-split solution can be.

    Did you in fact get a full room by room Manual-J heating & cooling load calculation on this place? If not, spending several hundred USD for an engineer or RESNET rater to run aggressive numbers on your place will pay for itself in reduced equipment size immediately, and several times over in the increased efficiency (and comfort) that comes with right-sizing the equipment. You can get a pretty good idea about the whole-house sizing by data-logging the duty cycle of the 5 ton system on afternoons when temperatures are near the local 1% outside design temperature, but that won't do much for getting the zone-by-zone numbers right.
     
  6. WorthFlorida

    WorthFlorida ?

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    You did not say if you have a one or two story home. As Dana stated about new refrigerant lines is a not always necessary. Really depends on the condition and age. When old lines are cut after they were evacuated there really isn’t anything in them. Some techs will blow nitrogen through them to to flush out anything that might be in them. As some might think, the refrigerant oils do not stay in the lines. By replacing the lines the warranty from your local dealer may be 100% for the first year, after that labor is not included even if the compressor goes out. With old lines and it leaks one week after the install, you be stuck with the entire bill for new lines plus refrigerant.

    Eventually there be no R22 available. As Dana mention a Manual J is needed but the clay wall that acts as a giant heat sink is the killer. A smaller system, say 4 ton will probably cool as good or better than your current system but those 95 degree days with the sun baking on the house, the 4 ton may come up short. There are two stage AC compressors so the second stage would kick in on those heavy load days. They are usually above SEER 18 and they do get costly but a good chance it will save you money on the normal days where only the first stage is needed.

    Split units are nice, the equipment cost may seem lower but to switch out so you have more zone or room control takes a lot of work. The cassettes usually need to be mounted on an exterior wall for the condensate drain lines. Then refrigerant lines needs to be run to each cassette plus power. And the wife, if there is one, may not want to look at these things on the walls. In your home perhaps one split unit for the clay wall room for when extra AC is needed could be an option and if you ever want to add AC for the basement or garage.

    It’s all the more reason to have your home evaluated with a Manual J and options laid out. Cost wise, in Central Florida where most are heat pump AC systems, the compressor and air handler replacement for a 3.5 ton would be about $5k-$5.5k at the top. They can be had for about $1k less if you shop around.
     
  7. Nathan Davis

    Nathan Davis Member

    Joined:
    Feb 22, 2018
    Location:
    Springfield, Missouri
    You all have guessed partially right. It is indeed a 3-story + basement, nearly uninsulated masonry building, but heavily insulated in the 3rd floor attic, reflective film over storm windows, and a full 2-story of add-on porches that provide shade across the west side of the house. But it's NOT zoned by floor--it's a single zone for the whole house.

    The man who replaced the A/C system in 2005 just finished leaving my house. He said they evacuated the line so well that it should be good for another 5-10 years since I use it only during the summer months. However, he said that the cold air duct going to the first floor is undersized (only 8x14) so 2005 he had to replace the 5 ton compressor with a 3.5 ton compressor because the system kept freezing up because the air flow was insufficient for a 5 ton system. No wonder the house is cooling insufficiently in August. I'm trying to cool down 4300 sq ft with only 3.5 tons, and the exterior walls are all masony, and the air flow is marginal! In 2005, he replaced the original system, but the ducting was all ready installed, and the previous owner refused to spend the extra $ to replace the undersized duct. I looked and confirmed that the air duct going to the first floor (1700 sq ft) is indeed only 8x14.

    I asked him to give me a price to install a new 18 seer Bosch 5 ton system, move the air-handler from the attic to a 3rd floor closet, and install a larger air supply duct between the air handler and the 1st floor (although the existing cold air supply duct is only 8x14, there is room for a 16x14 duct). So I'm hoping that if we increase the duct size, then we can use a 5 ton compressor, and increase the air supply to the 1st floor. And it will be really nice to access the filters from a closet rather than having to crawl through a hot attic.
    Does all this sound reasonable? I looked over the literature on the Bosch system (Inverter Ducted Split Air Source Heat Pump), and it looks good at face value. I probably would NOT use it as a heat pump but only as an A/C. I love the hot water radiators that we use for heat. They look right for this 100 year old house, and everything heats evenly and comfortably.
     
  8. WorthFlorida

    WorthFlorida ?

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    All new AC units must have a matching air handler for the most efficient operation. Some systems have intelligent boards at the compressor and at the air handler and if there is no match, the system will not initialized. Mostly true for SEER 18 and above.

    I had that though for this post about the duct work. One way that efficiencies increased greatly was the requirement for larger duct work to move more air at a slower rate through the air handler. You'll do better with the air handler on the top floor. It would be very difficult to cool the top floor with the air handler in the basement. Even with duct work at the ceiling of the top floor and bring it to the basement just doesn't work. I had a home in upstate NY and I purposely had the returns high on the wall when the home was built with a forced air system in the basement. AC was added later.

    I do not know anything about BOSCH units but just be wary. If it is a popular unit in your area then there be support and parts for it. The problem with a lot of German design product is proprietary parts and they are usually more expensive. (BTW..Carrier high end units have very expensive parts.)A tech may not get support from Bosch of he is not authorized or trained for their units. The AC guy you used before when he changed the compressor seems it be good and to call on him. I'm sure from his experience what would be the best manufacture to go with in your area. He would want something reliable so he won't have to make warranty calls, have parts readily available if ever needed plus he would want your referral.

    Still go with a heat pump, the price difference from a non heat pump unit maybe about $1k less but should your furnace crap out on the coldest day of the year, you'll still have heat. Depending on your fuel cost for the furnace the heat pump could be less costly to run. It can be set up from the thermostat if the heat pump or the furnace is the main heat source.

    This is what can happen when the furnace dies.

    https://terrylove.com/forums/index....n-the-heating-system-is-not-maintained.80045/
     
  9. Nathan Davis

    Nathan Davis Member

    Joined:
    Feb 22, 2018
    Location:
    Springfield, Missouri
    That makes sense. I'll still go with a heat pump for backup in case my boiler ever goes out. Right now, the air handler is in the attic above the 3rd floor. I assume that it would still be OK to put it in a closet on the 3rd floor?
     
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