Page 1 of 2 12 LastLast
Results 1 to 13 of 19
  1. #1
    Join Date
    Apr 2006
    Posts
    12
    We were spec'd for right between a 2.5 and 3 ton A/C. Due to the way our house heats up, room for loss improvements, humidity, and general temps here in Ohio, we went for the 2.5 ton system. This was 5 years ago. No problems to mention with this system, always keeps the house comfy although it certainly has limits. It has been unusually hot lately and there have been a couple days the A/C has run non-stop to maintain 75 inside. It has fun stright for over 12 hours on some days. Usually, the system runs a lot which was desired for humidity control, however it normally cycles when the temps are below the mid-90's.

    I guess my question is....Is it bad for a system to run non-stop for long periods of time? Granted, I probably couldn't cool the house to 72 with this system, but I don't think anyone would want to. Our electric only goes up about $50 in the summer so even though it runs a lot, it's not costly. Any thoughts on upsizing the coil while we're modifying the system? I personally don't want to, but we may sell the place in a 5+ years and wouldn't want any problems from something like this.

  2. #2
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,213
    skin

    If load calculation was performed correctly and BTUs required were between a 2.5 and 3 ton, then your dealer did you a disservice by installing a 2.5 ton. A 3 ton would have been a better choice.

    Is it bad to run constantly? It can reduce the life of the unit, it definitely is bad from a comfort issue if it can not maintain your normal stat setpoint, and of course you will have high electric bills.

    I saw your post about a heat pump add-on. Here again a 3 ton HP is a better choice for both heating and cooling. And you must have the correct matching coil for size/SEER, preferably of same brand. Your dealer does need to check your ductwork to make certain that the upgrade to a 3 ton will not create any problems.

    IMO

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,302
    Sounds properly sized to me. Cycling below the mid 90s, holding temp at the mid 90s for Ohio means it is right on the button. Our office often runs 12+ straight hours in the summer. Not hard on them, starting & stopping is more wear & tear actually.

  4. #4
    Join Date
    Feb 2004
    Location
    Central Kansas
    Posts
    1,145
    "Is it bad to run constantly? It can reduce the life of the unit, it definitely is bad from a comfort issue if it can not maintain your normal stat setpoint, and of course you will have high electric bills."

    Glad Baldie set it straight, the above statement is far from truth. Repeated start/stop is what wears out equipment, causes high amp draw & energy consumption at each start up, low operating efficiency until several minutes of run time have elapsed, etc. Look to ventilating your attic or adding a little more insulation. If any disservice was done it was that perhaps these factors were not looked at to assist in evaluating your HVAC system needs. When all people do is look to change out systems without looking to help reduce the loads placed on them, only part of the equation is being looked at.

    "Bigger is better" applies to paychecks, not HVAC equipment.
    Don't confuse me with facts, my mind is already made up.

  5. #5
    Join Date
    Dec 2004
    Location
    Derby City
    Posts
    3,964
    tigerdunes: obvious why there is no 'professional' next to your name. Now don't get testy, but virtually ALL the answers you gave were wrong. At least you indicated it was your opinion and only that. You are getting 'personal' though when you state "the dealer did you a disservice by installing a 2.5 ton." Nothing could be further from the truth!

    For your information, having virtually ANY electrical applicance on and running is less wear and tear than having it kick on and off over the same period of time. If a system is 'properly' sized, then when it is under high load conditions it should run virtually non-stop. The key to this is the fact that it is continuing to satisfy the thermostat requirements. That in and of itself would not indicate an undersized system.

    For the same reasons you are wrong in your assesment that the life of the equipment will be shortened. In fact, it may prolong the life of the system or at least minimize mechanical failures.

    You one observation that the ductwork should be checked is correct. (I believe in giving credit where it is due.) Although 1/2 ton in size is not critical, it would be conscientious for the contractor to verify air supply and return to maximize the operation of the system. It certainly would not hurt to do so.

    But soulds like midwest said it all as well. Unfortunately, someone out there will listen to what you are saying and believe it to be the truth. Advice such as yours is what keeps our industry and service departments busy. All the best, John
    Everyone has a purpose in life..........even if it's to be a bad example.

    Seek first to understand, before seeking to be understood.

  6. #6
    Join Date
    Jun 2006
    Location
    right, here! in the heartland of the homeland!
    Posts
    737

    chuckle chuckle

    most people that say check the duct systems are the ones that either seen a hvac contractor short change, the general contractor by undersizing the condenser one ton and putting the air handler and ductwork backwords among undersizing the duct work, to get the bid, or slam and jam, which may be not the case at hand or may be that is or may not b da question,
    stirring the pot, im bored!

  7. #7
    Join Date
    Feb 2006
    Posts
    468

    What all except TD said...

    If it holds 75 in the heat pretty much the whole country's been having and you are happy with 75 AND it's only costing you $50, you are in HVAC heaven. Constant operation is fine and great for dehumidification. Chances are that the extra dehumidification derived from constant operation will provide comfort even if the indoor air temp is a degree or two above setpoint.

    Slightly undersized HVAC is optimal for comfort and efficiency, assuming one can get past the fact that for a couple hours during a couple days all year the system might not make setpoint by a degree or two. Bigger ain't better!

    Try this analogy for constant verses intermittent operation: The wheels and everything else fall off of cop cars, taxicabs and soccer mom minivans driven only around town 75-100k miles, whereas long haul truckers can run a million plus miles, even though they max out the engine for minutes at a time pulling long grades.

    When does the blue flash of a dead incandescent light bulb nearly always occur...when you hit the switch turning it on, NOT while it is already running.

  8. #8
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,213
    I have a great deal of respect for BaldLoonie's advice and he will forget more than I will ever learn or know about HVAC. But I think it's always good to have more than one opinion especially from a homeowner's viewpoint and I certainly stand by mine.

    First of all AC or HP is sized by cooling load and while there are many factors to be considered, one of the main ones is the average high temp for the climate you live. If "Skinny's" load calc was truly performed(which I doubt) and he was in between a 2.5 and 3 ton unit, then why would the dealer size down rather than size up which seems more reasonable. People who have or want AC expect to be comfortable. That is the main reason for having air conditioning. Yes, I believe the dealer did a disservice to "Skinny" unless Skinny participated in this decision. You see too many of these same situations on this forum though.

    As far as life of unit goes, I said running a unit continuosly "can" affect the life. I believe this. Obviously, if your normal thermostat setpoint can not be maintained, then your normal comfort level can not be maintained. And a unit running continuously will drive up one's electric usage.

    I realize that practically the entire nation has seen some extraordinary high temps over the past several weeks but a unit that runs straight for over 12 hours is not normal. Skinny was probably slightly undersized to begin with and these high temps just exaggerated a poor situation.

    Difference of opinion is what makes a market and hopefully those that read this thread can make up their own mind from the information shared by all.

    Respects to Baldloonie,MidWest, and John Lloyd.

  9. #9
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,942
    You don't know the criteria that the dealer used and to call it a disservice is not right. Load calcs are not done at the highest temperature that house will see, but the design temp which is fixed per the environmental conditons.

    For an AC or HP, running continuously does not shorten the life. Starting torques and currents on the motors and components creat the worst stress.

    A unit that runs straight for over 12 hours should be normal.

  10. #10
    Join Date
    Apr 2006
    Posts
    12
    Well, if you look at the 2nd sentance of my original post, I state that I was involved with the decision to go with the 2.5 instead of 3. I know I can improve the cooling with better attic ventilation/insulation (it's a 140 year old house...) and have done quite a bit of work since the system was installed. Also, the house tends to becomes humid more than HOT so longer cycles were desired and the installer agreed with my decision.

    What has panned out is that we've had no problems in 5 years, avg. $50/month electric increase during the summer, and the house will typically maintain whatever temp I dial in. Seems great. To maintain that temp on 95 days it will run non-stop for long periods of time. I just hadn't expected it to run 12 hours at a time and was concerned it might cause problems with something freezing up, etc.

    My other concern is that since the house seems more difficult to heat than cool, the 2.5ton coil may not be enough if I add the HP.

  11. #11
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,213
    Midwest & Baldloonie are right! Sounds like your system is just about the right size. The key is your statement that the unit normally cycles on days it's below 90 degrees. That being said indicates the system is oversized any other time the temperature is below 90 degrees. Like someone else also said, your best bet is to tighten up your weatherstripping, and add more insulation etc. This will help on days above 90 degrees.

    Thorton
    __________________
    Life is not measured by the number of breaths we take,
    but by the moments that take our breath away

  12. #12
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    1,395
    If you are very serious about the heat pump i would look for a 3 ton 2 spd. From what you are saying this will operate in 1st stg 90% of the time which is (depending on manufacturer) approx 60% capacity.

    Since you state humidity is your biggest problem make sure the system matchup you choose is rated to meet or exceed the latent load of the system, then get as close to the sensible load as possible. This will change depending on what coil and/or blower system you have.

    Do as much more bldg improvements as possible before performing the next heat load calc. I'm guessing you want the heat pump for this coming winter. You have approx 2 months before we start getting very busy with the heat season. Plenty of time to at least come up with an envelope improvement plan and realistic timeframe when it can be accomplished.

    There is information from the US Dept of Energy, Cal Dept of Energy and Fla Dept of Energy that deal with ways to improve your home for energy savings and comfort. If someone has the links please post them for skinny2.

  13. #13
    Join Date
    Dec 2004
    Location
    Derby City
    Posts
    3,964
    interesting that humidity is indicated as a concern, however, some are quick to move up in size with no thought given to the effect on latent abilities. The larger the system (if oversized) then the poorer job of removing latent (humidity) heat from the space. Just another reason to be properly sized. Not over or under. So, what's the problem with being right where you need to be? Good differences of opinion, but where I draw the line is where opinion is offered up as a basis for making a decision. Just an observation. One of these days, everyone will acknowlege (even those of us in the industry) that there is a little more to this HVAC thing than a W.A.G.!
    Everyone has a purpose in life..........even if it's to be a bad example.

    Seek first to understand, before seeking to be understood.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event