New construction need advice please

Discussion in 'General Discussions' started by 2106, Sep 3, 2020.

  1. 2106

    2106 New Member

    Hello, this is my first post.

    Looking for advice,

    Building single story with full basement 2500 sq-ft residence in central Maryland. Unfinished, unconditioned bonus room above garage (with duct work to it but no current plans to finish) and possibility of a future clubroom (20x25 ish) and bath in basement. Clay soil, no shale, few rocks, drains well, conventional septic system.

    Geo contractor (interviewed several) says horizontal or vertical system will work on my lot. Totally up to me. Small savings perhaps $75-100 per year with vertical system being somewhat more efficient. He ran his computer model using my house plans.

    I have decided on vertical system for 3K additional cost. I believe it is a better system by being deeper than 6 feet , not tearing up the yard and worry about soil conditions affecting the soil heat/cooling abilities as well as and any future tree plantings or home additions as it keeps the Geo source in a compact defined area. Recommended is 560 feet of well with 3.5 ton Waterfurnace series 5 single stage compressor with variable speed blower. Single zone system.

    Optional (I asked about 2 speed unit upgrade) is 4 ton series 5 system with two speed compressor, variable speed blower and 640 feet well. This will cost 2k more and yield savings of $10 or so per year.

    I prefer to have house windows open when possible. There will be a gas fireplace in the main living room where most time will be spent and for some supplemental heat on cool mornings or evenings or when desired etc.

    I don't see the need for a two zone system. Reliability and solid system with as few bells and whistles is fine. Don't want more to go wrong and costlier to repair.

    Opinions please. Thank you.
  2. SShaw

    SShaw Active Member Forum Leader

    Clay is nearly ideal soil for geo, so horizontal should work well also. Your rationale for vertical makes sense though.

    I would probably opt for the 2-stage system plus a variable speed flow center. Two-stage is more about comfort than savings, but I would think the savings would be a little more. The variable speed flow center should save at least $50/year.
  3. Deuce

    Deuce Member

    I would definitely go with 5 series, 2 stage. I have that and it rarely if ever goes into 2nd stage. I am on the VA Outer Banks.
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Concerning that a contractor states that vertical is more efficient than horizontal. One can make a horizontal system much more efficient than a vertical, and vice versa. It all depends how it is sized. It is easier and cheaper to oversize a horizontal loop field, but it does not make much sense. You get quickly to the point of no return.

    It is simply a matter of preference, horizontal requires a larger footprint, thus more yard restoration. Usually not an issue in new builds due to contraction work affecting the yard anyway.

    There are few things pointing that your contractor is not really in depth with geo. How can a dual stage unit require 80 ft more borehole, but only save $10 annually?

    The potential savings come from having a more efficient unit, and using less compressor heat, thus extracting more heat from the borehole, theoretically requiring a longer borehole. But the larger borehole versus savings ratio is off. Also the 560 ft versus 460ft is telling, he puts a load number in a software program, with a lot of assumption being made for him. Ask him what grout conductivity are used in those calculations, which are an important parameter in determine the loop length, and I bet you a nickel he would not know. In reality you don't need a longer borehole, since you do not pause the loop since the variable speed units are running much longer and don't cycle as much, and therefore have a more continuous heat draw from the soil surrounding the borehole.

    All that would not mean he would not build you a great system.

    What is concerning is the recommendation of a single stage, it will deteriorate you geo experience, both in terms of efficiency and especially comfort. Get a dual stage or even better a variable speed 7 series. Get a variable speed circulation pump.

    If you are on a budget, pay for those 2 things by putting a horizontal loop field in.

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