Help selecting size in SE PA

Discussion in 'Quotes and Proposals' started by rhk109, Aug 22, 2014.

  1. rhk109

    rhk109 New Member

    Hi, new to geo and these forums. I'm considering replacing my aging air source heat pump with propane backup. I've gotten a few quotes and 2 companies who performed load calculations. Both heating load calcs were performed by geo only firms and came to ~38k Btu/hr for 2300 sq/ft home. Firm A recommends a 3 ton system and firm B recommends 4 ton. They're both pretty adamant that they are "right". I've followed up with both of them to understand their justifications. Here's the summary

    Firm A: 3 ton system is sized for 95% of the heating days/year. 4 ton is oversized and too big for cooling load.

    Firm B: 4 ton system is sized for ~100% of heating days/year and the aux should only be needed for emergencies for extreme cold weather.

    How do I make an informed decision? What other info do I need?
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Hi and welcome.
    You need firm A to provide you with the anticipated electric usage to cover the 5% of heating load per year, add that to your install cost and compare to the cost of covering 100% of the load from company B. Covering 100% of the load with geo is often not cost effective when compared to even 10% coverage by auxillery heat. It is a choice not a right or wrong scenario. In my world choices are fueled by economic impact, not emotion.
    Hope this helps
  3. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    An informed decision depends on your strategy. I like sizing for the cooling load and then add the projected heating load with my second cheapest fuel.

    I am not sure why A and B are sizing to heat.

  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    If your 38 Kbtu/h is correct, firm A is correct. You only drop down in the single digits a few times a year, it does not make sense to install that capacity when you use it only a few days per year. A 3 ton usually runs more efficient, you need lesser pumping power and despite some electric heat, in your case about $20-30, you will save about $100 annually in operating costs. In addition, you save upfront installation costs.
    Variable speed technology changes those dynamics a bit, what equipment are they providing?
  5. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Sizing to avoid auxiliary use is often folly in that you can actually spend more running a larger compressor all the time vs a little auxiliary once in awhile. I would submit that the individual recommending a 4 ton is unevolved in our field.
    with that load in MI I would ask the following question: What can we do to get it down to 2 tons or 2.5 tons?

    Start by seeing if their is an opportunity to reduce load at your home, the cheapest ton is the one you don't buy.
  6. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I second the motion to go no higher than 3 tons and investigate ways to drive load down from there. Clients not in MI can reduce load, too. In approximate order of importance deal with:

    1) infiltration (air leaks in and out of home)
    2) Ensuring ducts are within thermal and pressure envelopes, or, failing that, very well insulated and substantially leak-free.
    3) ceiling / attic insulation
    4) Fenestration performance (windows and doors)
    5) wall insulation

    None of this cares a whit about system type, size or efficiency. Echoing Joe, the cheapest Ton is the one (or two) you don't need, buy, install, operate or maintain.

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