3 ton vs 4 ton delima

Discussion in 'Quotes and Proposals' started by gbuck, Feb 6, 2011.

  1. gbuck

    gbuck New Member

    Getting quotes on switching to geo. All but one contractor sais 3 ton. Our home is a 2100 sq ft two story, with propane funace. All bids so far want to go with three 150 ft vert wells. I'm all about saving money, but want to make sure I get it done right the 1st time. The 4 ton contractor sais the main reason is an unfinished block basement. His bid for a water furnace two stage, desuperheater is about 5k more than a Carrier 3 ton 2 speed, desuperheater. The carrier guy swears we dont need 4 ton will have ac problems in summer. The 4 ton guy sais if we go 3 ton we wont even have enough heat for water heater. Getting frustrated, this shouldnt be rocket science. Home is 10 yrs old, decent.insulation and new topend replacement windows. Any thoughts?
     
  2. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Ask for the Manual J heat loads from each bidder. Then we can help you sort out the best choice.
     
  3. bobpietrangelo

    bobpietrangelo New Member

    What is your heat and cool load. Is everyone offering 2 stage equipment, for the WF unit does the cooling load fall between the stages? Are you in more of a cooling or heating dominated location? Which contractor has the most experience? What have their references had to say about their work and reliability?
     
  4. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I just took a job near C-bus

    Where are you? I may come take a look.

    Mark
     
  5. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    My gut leans toward 3 ton based on info provided, but a Man J load calc is needed.

    I'd be a bit concerned about 4 tons on 3@150' bores if the load really comes in at 4 tons heating.

    It may be possible to back calculate load from propane usage compared with degree days, but not if propane usage data is muddied by other appliances.
     
  6. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    With the very little you offered, 3 ton makes sense, however would need more info to swear by it.
    J
     
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Desuperheater "steals" about 10% of heating capacity, it would continue to heat your hot water, you aux heat would just kick in earlier.
     
  8. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I'm forever skeptical of the blanket generalization in re DSH diversion - it comes down to water use patterns and buffer tank temp in real time.

    The 10% diversion is a reasonable approximation - on WF docs it assumes a 90 degree buffer or entering DSH water temp. Outside of 90, things change.

    On a really cold night, chances are the buffer will heat up well above 90, reducing the diversion at a time when the extra heat is useful for the home. In fact some systems dump the DSH when its EWT hits 130 or so - life is good.

    Looking at this from another angle, suppose diversion does cause a bit more aux operation - this is actually fairly likely if early risers shower / bathe on cold mornings. Consider that the hot buffer water flows into the main water heater - those showers are had with little or no energy use by primary water heater. Aux use is offset by (non)use by main water heater - life is still good.

    Bottom line, I don't advocate any upsizing on account of DSH option or use.
     
  9. gbuck

    gbuck New Member

    I just got the maual j results back. The high load btuh 58312, and the cool side is 25620. I have all kinds of other datA available. Let me know if this helps.
     
  10. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Assuming the manual J is accurate, with Columbus Ohio weather data, desuperheater (yes, when running in 2nd stage it will "steal" 3.500 BTUs from the 4 ton capacity), I would see it as difficult to justify a 3 ton unit. I would recommend a 4 ton system. With 3 tons, I am showing 27% Aux heat use....
     
    Last edited: Feb 10, 2011
  11. gbuck

    gbuck New Member

    HIs numbers came up with the geo being able to come up with 98% of the load. 4 ton would handle 100% but would never pay for itself, seeing how the 4 ton would run on more electric to operate would nigate the savings.? Does that sound right.
     
  12. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    How old is the house?

    If the Man J 58k heat load is the real deal then 4T is likely the better fit.

    58k sounds very high for 2100 SF in Columbus, hence my question about the home's age.
     
  13. gbuck

    gbuck New Member

    the home is 10 years old, just replaced windows with high end replacements, if it matters. dont care to spend the extra on a 4 ton, however have been told that oversize can be bad as well. getting frustrated, was hoping having these manual j numbers would finalize everything. just seems to bring up more questions.
     
  14. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Whon provided that loss calc?
     
  15. gbuck

    gbuck New Member

    Local heating and cooling company, hate to put out names. Call me 6145803164
     
  16. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Age and window replacement militate more toward 3T, unless there is a lot of glass.

    All this is mere conjecture absent a load calc.
     
  17. gbuck

    gbuck New Member

    if you have a fax, i'll be glad to send it you.
     
  18. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    My point is you need each designer to conduct their own load calcs so that they "own" the results.
    GIGO applies to software generated calcs so more than one is in order.
    j
     
  19. gbuck

    gbuck New Member

    the guy who gave the 3 ton quote is the one who did the calc. have seen no calculations form the guys who push 4 tons. i guess they both would probably would work, the question is which one is going to more efficient. Going the smaller tonnage, saving on kws/month vs running compressor on larger unit, using more kws per/month but less likely to use aux. heating. I just wish it was an easier choice. Do i run a risk of not enough buried line on the 3 ton and using up the heat/cooling in ground?
     
  20. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    That sounds right but doesn't square with a 58k Btuh heating load
     

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