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  1. #14
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,530
    Are there any improvements that you plan to do with insulation I attic or walls?

    I did note that you have vinyl windows already so adding some insualtion to the attic is very cost effective and will help on the load on the home.

    I will give my home as example for base comparaion since I can't see your home. My home was built in 1978 and I have owned it for 12 years. 1784 heated square foot. When I first purchased it had double metal windows and (3.5) ton unit.

    Fast forward to now and I have changed out windows to double vinyl and added add. Insulation to the attic. Now per manual j I have a (2.5) ton Trane system installed and it works like a champ with electric bills no higher then $100.00....

    While my home is not yours I live in the same region you do which is northeast la.. Our design temp for summer is 95 degrees. I would be willing to beat that your home as it sets today does not need a (3.5) ton system but since I have not ran a load I can't say that's it is acrate sized.

    So how guess the request for a load cal. Or have they come up with excuses not to run one?

  2. #15
    Thanks everyone for the replies. I'm appreciative of the feedback and the learning experience this has been.

    I've requested a load calc from the vendor I've been dealing with. I'll let you know what he comes back with. One follow up question. My current system does have a leak in the coils (part of the reason why I'm looking at a new system, along with it's overall age and inefficiency). Will this affect or influence the load calc results?

    Interesting that I've had 3 companies come give me quotes and none have offered to do a load calc.

    I've included electric bills from the past two years for reference.

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  3. #16
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    1500sqft shouln't need more than 3 tons. In my climate it would be 2 tons in most cases.

    It's hard to use that utility bill because we don't know the actual effceincy of your current unit during that period. SOmeone would have needed ot measure the return wet bulb temps, the supply temp and the power consumption of the condenser and blower. I also don't know what indoor temp you used.

    With two oversized 3.5 ton 10 SEER units on my home, I was at 2500kw-hrs. I acutally only need about 3.5 tons total and currently have two 2 ton systems. Design temp is 93F here.


    I bet your right at 3 tons given the age of the system, the hot weather (equipment is less efficient in hot weather) and those average temps.

    Let say you had a unit with a average EER of 8. IF it ran about 60% of the time in the hottest month, that 432 hours. A 2 stage unit would run almost 75% of the time in either 1st or 2nd stage. 36,000BTU with a EER of 8 is 4.5 kw total power consumption. That's 1944 kwhrs. With a average EER of 14, that drops to 1110. That's a savings of 833 kwhrs or at your rates about $130 in the hotest months. Your summer rates are just as high as mine. I'd look at getting at least a 15 SEER system, 16 SEER 2 stage even better for comfort in your humid climate if you can afford it.

  4. #17
    So I rescheduled appointment with the guy and company I've been working with to have the load calc done. The guy came out today but didn't do the load calc. Just quoted the 1 ton per 500 sq. ft rule of thumb. He made it sound like a bunch of different variables (attic insulation, wall insulation, window type and placement, etc.) go into coming up with the load calc. Obviously he wasn't prepared to do the calc. My sense is he's more of a salesman than a technical HVAC person. I went ahead and asked him to give me some quotes on the Trane XL15i and XR16 in 3.5 and 3 ton units, respectively. Will see what he comes back with.

  5. #18
    Update: Just out of curiosity, I called another HVAC company (BBB A+ rated) who I've never spoken to or worked with before to tell them that I'm interested in replacing my HVAC system and would they come do a load calc to ensure proper sizing. Basically got the same answer as others, don't really do load calcs on small, simple residential homes like mine. Sounded like they only do them on big, complex situations (i.e., commercial, larger 2-story homes, etc.).

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