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  1. #1

    Heat pump sizing issues and moving

    Bit of a long question so bear with me. We are just about to break ground on a in-law suite 1300 sq ft one floor spray foam insulation through out. The HVAC contractor has quoted a 2 ton heat pump. The heat pump in the main house is a 3.5 ton about 2years old York. My sister has a 5 ton York about 5 years old that she has just replaced the compressor in, and is having it removed because she is switching to gas. Do you get where I am going here? Would it pay to have the 3.5 ton moved to the in law suite, buy the 5 ton from my sister and put that in the main house which is currently 2500 sq ft soon to have the attic finished which will add approx 800 sq ft.

  2. #2
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    21,765
    I see where you are going here... however IMO it is not a good road.

    Sizing of equipment is more about heat loss and heat gain than sq/ft, each structure is unique.

    You could have an energy auditor go over your home (and the prints for the addition), you could pay a heat and air guy to do load calcs for you, or you could click on the 'HVAC Calc' link above (menu strip), pay the $$$, and run your load calcs.

    Thought: SR citizens like HOT heat in the winter... If you have gas available... he/she (senior) would probably be more comfortable with gas heat.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  3. #3
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
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    5,350
    Quote Originally Posted by Jetuph View Post
    Bit of a long question so bear with me. We are just about to break ground on a in-law suite 1300 sq ft one floor spray foam insulation through out. The HVAC contractor has quoted a 2 ton heat pump. The heat pump in the main house is a 3.5 ton about 2years old York. My sister has a 5 ton York about 5 years old that she has just replaced the compressor in, and is having it removed because she is switching to gas. Do you get where I am going here? Would it pay to have the 3.5 ton moved to the in law suite, buy the 5 ton from my sister and put that in the main house which is currently 2500 sq ft soon to have the attic finished which will add approx 800 sq ft.
    To accomidate what your talking about, your would have to have a massive duct renovation.
    Plus, the blower that moves the air in the system may not be large enough to handle the 5 tons of air required.

    Spliting the addition and the main house, on two different systems, is what I would suggest.


    As far as your sister goes, I would suggest for her not to remove her heat pump. She should install the gas furnace, and use a combination of gas/heat pump.
    It will maximize her efficiency.
    Her contractor would be able to explain in more detail.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  4. #4
    Thanks Ga I'm thinking the same as you, but I thought I would ask the experts. I hate to pass up a good deal, but in the long run it may not pay. BTW we are the not so senior citizens moving into the in law suite with my daughter and her family taking over the house. We are thinking radiant in the in law with the heat pump for air and spring and fall cool days.

  5. #5
    Thanks Vegas ,
    The in law suite is a separate building/ garage.

  6. #6
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    YOU WILL want a separate system for the inlaws! If they are like most old people, they want it 72F in the summer and 75F in the winter. Give them their own unit and thermostat.

  7. #7
    Join Date
    May 2004
    Location
    south louisiana
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    3,327
    read post #4 motoguy.

    putting the 5 year old 5 ton to replace the 2 year old 3.5 ton in original
    house is a bad idea. the original house's ductwork is sized (hopefully)
    for 3.5 tons of air. the 2 year old unit is probably more efficient than
    the 5 year old unit.
    if the original house is comfortable..leave it be. let someone else
    have the headache of a used unit.

    as to the inlaw house..3.5 tons is way too much
    if you have 1300 sq ft and all foam insulation
    walls, roofline..is this place on a slab or crawlspace?
    I'd look into a mid efficiency (15 to 17 SEER) heat pump with
    variable speed air handler.
    are you in planning stages now?

    its never a good idea to start moving and switching units IMO.

    if you put your location it helps.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  8. #8
    Join Date
    Jan 2009
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    Keokuk, IA
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    That's what I meant. He needs 2 systems. Leave the existing system alone and put in a properly sized system. Given the construction, most likely a 2 ton 2 stage would fit the bill, but a load calc is best since it's new construction.

  9. #9
    Thanks so much for the input. The location is north of Philly about 40 miles. The new construction is going to be insulated slab with radiant. What opinions can you give on tankless water heaters with regard to radiant and domestic hot water vs a tank heater all running on propane?

  10. #10
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    If you're on propane, I would go dual fuel and use a heat pump down to around 35F then supplement it with a hydronic coil down to about 10F or wherever you blaance point is. Then supply the balance of heat with radaint floor.

    For a small space and combi wall boiler would be a good option. I'd one from a boiler mfg, not a tankless mfg. If will last longer and give you less issues. Get one with a outdoor rest control that lower the water temp based on outdoor temperature.

    Defintiely use a heat pump if you have propane.

  11. #11
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    21,765
    Quote Originally Posted by Jetuph View Post
    Thanks so much for the input. The location is north of Philly about 40 miles. The new construction is going to be insulated slab with radiant. What opinions can you give on tankless water heaters with regard to radiant and domestic hot water vs a tank heater all running on propane?
    Heating with Propane is costly... and propane in furnaces tends to have more maintenance issues (propane is 'dirty' as compared to gas).

    I can only speak for Rinnai... they are NOT designed for heating... unless you get the special one. Better get a boiler designed for this application.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  12. #12
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    Rannai has been pushing their unit as a combi with their air handler was well. But I don't see their heat exchanger being robust enough to handle heating duties long term. I doubt it woudl last more than 8-10 years. While a good tankless used just for water with proper maintenance should last 15-20 years. A combi should have the primary heating loop seperate from the domestic water heating look using a heat exchanger.

    I think some comparisons were done with The cost of propane vs. stright resistive electric strips and the all electric was cheaper.

    Did you consider geothermal? If your already digging for the foundation, you mgith consider adding groudn loops. It won't take too much for a small, well insulated home like this. You can make hot water for some supplemental radiant too, but you'll want to use a air handler for most of the heating load.

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