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  1. #1
    Join Date
    Nov 2007

    Hmm Residential HVAC replacement help sought

    Have an old (23yr) heat pump system, inside unit is time bomb with rusted, leaky drip pan, clogged/moldy coils, and high vib. fan. Live in MD. Outside unit is newer (est. about 8 yr old). Want to go to dual fuel option -- either heat pump with gas furnace or heat pump with hydronic boiler for heat and DHW. Water heater is also 23 yrs young, electric. Have gas newly piped to mechanical space for possible boiler, furnace.

    A few questions and issues come to mind from the few quotes I have received thus far, and looking for general guidance (and perhaps ground truth on a couple).

    1. Replace entire system to include the outside unit. Most money, but can then get a matched system, more efficient system (current outside unit is 10 or 13 SEER, no one can tell me yet) with more warranty. Go with new gas hot wtr htr.

    2. Keep current outside unit, get new gas furnace/air handler, new inside coil. Use as AC/heat pump until outside unit fails then replace both inside and outside unit with 15/16 SEER R410 equipment. New gas Hot wtr htr.

    3. Keep outside unit as AC only and get new gas furnace, inside AC coil. Convert to dual fuel heat (heat pump) when outside unit dies. New gas hot wtr htr

    4. Go hydronic option. Dual fuel heat pump, gas boiler for heat (hot water coils above air handler) and DHW. Advantages for this is one gas appliance. Disadvantage is price and complexity. Looking at Munchkin or Triangle Tube boilers. Have one recommendation for Quietside on demand HW heater with storage tank but have not heard good things about that product.

    Know that is a lot to process but am looking for some general pros/cons.

    One specific issue that I would like to throw out there concerns the 5/16 inch Heat pump line running btwn inside and outside. The "newer" outside unit had a 3/8" connection but the 5/16" inch line is brazed/welded. Should this line be replaced/upgraded to 3/8" (what about for R410). Other line is 7/8". How much efficiency is lost to that missing 1/16" if a 16 SEER Heat Pump system is installed. Replacing the line is doable by only digging into finished basement drywall cieling, about a 40 ft run.

    Thanks for any help,

    Searching for info John

  2. #2
    Join Date
    Jun 2007
    Round Rock
    Get as much done as you can afford. You're going to spend it now or spend it later. Better to spend it now and reap the benefits of the efficiency of a new matched system. If you go R410, you definitely need to change to the 3/8" line. I would do it no matter what you go with, but definitely 410.

  3. #3
    Join Date
    May 2007
    DC Metro Area (MD)
    Some people just flush the lines with RX-11. I'd prefer a whole new lineset if possible, though.

  4. #4
    Join Date
    Nov 2007
    Quote Originally Posted by RyanHughes View Post
    Some people just flush the lines with RX-11. I'd prefer a whole new lineset if possible, though.
    Thanks for the feedback.

    That was another question I had. Flush vs. Replace? Pro's I have talked are split on this. Oil contamination from an incomplete flush (can it be complete?) would probably not manifest for years (ie: year 11 after warranty expires). Do warranties exclude R410 systems installed with "flushed" old refrigerant lines?

    My original question concerned the size difference. How much is efficiency impacted by not upgrading/replacing existing 5/16" line with 3/8" line?

  5. #5
    Join Date
    Apr 2007
    Langley, BC, Canada
    I would have to agree, change the entire system now, save you a headache later.
    I would highly recomend you change the whole lineset. Each manufacture has there own recomendations for proper piping. Thereis a calculation you can do with a nomograph to determine how much pressure drop you will have through the lines, however lke I said, replace the entire lineset, will save you trouble down the road, especially if you go with a R-410A system. The POE oil in the new system will srub the old piping clean and deposit the debris either in the compressor and form acid, etc. Or clog up the TX valve.

    If you elect to change just the outside unit, and go with the 410 sytem, i give it about 6 months before you have to replace the coil, 1) 410 cannot be used with a cap tube system, if it is indeed one
    2) the contaminents in the piping and any remaining mineral oil, AB oil will cause problems.

  6. #6
    Join Date
    Jun 2007
    The Twilight Zone

    I live in Bel Air, Harford County.

    I replaced a functioning 21 year-old, 7 SEER, Trane Executive Weathertron heat pump in June. I combatted the 65% rise in MD electric rates with a 14 SEER Goodman. In August '07, I reduced my kilowatt consumption by 42% compared to August '06.

    I had to replace the old liquid line because it was only 1/4" and the new systems require 3/8". I kept the old suction line.

    I stayed with R22 refrigerant.

    In my opinion, a 14 SEER/12 EER offers the best combination of purchase price and true operating costs. Your operating costs are determined by EER and not SEER in the summer, and HSPF in the winter. Go for 12 EER and 9 HSPF. I would get gas back-up if you go with a heat pump.

    FYI, a 16 SEER has a dual stage compressor, a 19 SEER has dual compressors, and a 15 SEER and below has one single stage compressor (as do most systems in use today).

    Best to you.

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