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  1. #14
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by ootyboy View Post
    One of the contractors told me that he will run a a load calculation, but they are all adamant that given our house (ceiling height, windows, flooring) etc. a 5 ton unit is the minimum. All three companies I am working with are local, so they know the area very well -- but I am really afraid that they are all playing it very safe by over sizing the unit...

    Unfortunately, they are all wrong. If your design temp is 85F, then the system should be running constantly when it's a sunny 85F afternoon or warmer. A 5 ton will still be cycling on and off. You don't design for 100F just because once every few years for a couple hours it might get that hot.

    That's like buying a minivan to commute to work every day because of the off chance that your wife's van is being repaired so you need a spare. That's what rentals are for. Or buyign a pick-up because once or twice a year you go to Lowes and buy a bunch of lumber. That's why you have that stuff delivered. You get HVAC systems... and vehciles... for what their primary design or what you need them for is 90-95% of the time... not for the 5%. I'm not saying yu only buy practical cars or equipment. You can pruchase featurs based on comfort or preference. If you really love how that minivan drives and rides, than commute in that. Or pick a motocycle, corvette or BMW.

    I have a 3200sqft, 2 story, 86y/o old home, I'm in SE Iowa with design temps around 93F, with high ceilings and I don't even need 5 tons. About 4 tons total. And I can cinfirm that based on run time this summer in design conditions. Although the contractor that the previous owners used must have been trained like that one... they installed 7 tons total capacity.

  2. #15
    Join Date
    Dec 2011
    Posts
    15
    Thanks for the feedback Motoguy. I have been considering changing the Koi pond pump to something with less energy usage -- but I really need the high flow rate to keep the fish alive -- Catch 22!!

    Not sure if this is relevant, but one of the contractors was making the argument that since the furnace is modulating/variable model -- it ranges from 40,000 BTU to I think 100,000 BTU -- then even if it is oversized it will adjust down appropriately. The same is true of the A/C unit that is a 2 stage model. Anyway, I am not sure if I buy the argument -- if the unit is capable of 100,000 BTU and has a 5 ton blower -- but is always running at a lower speed/flame -- it is still using way more energy than a properly sized unit that is running at its peak efficieny --

    Thoughts?

  3. #16
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,159

    The logic escapes me

    You have done much of the insulate/ seal and you are considering installing the same size equipment because you are not comfortable?

    seems from the report , whose graphics don't give numbers to better understand, has identified the leaky ducts as your main problem.

    With the low heat and cooling loads for your marine climate zone, I would suggest you first attach the ductwork issue with the existing equipment wioth an eye to trying to overlap systems so they share rooms. Think of this as a primary/secondary or stage 1 and 2 system approach. With a high heat loss of just 40,000 BTUs it doesn't sound to me like super high efficient equipment is going to mean that much in savings.
    You might be fooled into thinking that if you have a duct problem that is fixed along with the new equipment and you hope it was all the extra money you spent for the equipment that dic the trick SO

    Fix the DUCT FIRST then figure out if you'll really see any ROI for new equipment Try top get the #T to do most of the home
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

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