Help in Picking Replacement Central HVAC system

Discussion in 'HVAC Heating & Cooling' started by QC91, Nov 24, 2016.

  1. QC91

    QC91 New Member

    Nov 24, 2016
    Hi, need Help in picking replacement Central HVAC system for our house the Square footage of the home is 1,990, and the zip code is 94520 for our climate we get 80, 90, and low 100 degrees in the summer, in the winter we get upper 30 to 40 degrees at night our home doesn't have good insulation in attic but did have newer dual pane windows with low e glass, our current HVAC system is Rheem from 1972 or 1973 the Natural Gas Furnace Model number 3010 125 HDA input is 125,000 BTU, and the Bonnet is 100,000BTU the outside condenser Model number is AT42B1 not sure if that is 4 Ton unit, also seeing that the new HVAC system are so much more Efficient would we need smaller system? I was looking at Different ones we will have HVAC contractor install it but wanted to do some research I found this one Rheem 95% 98,000 BTU 2 Stage Furnace + 4 Ton 15.1 SEER A/C on Ebay item number 182163860369

    any help would be appreciated
  2. WorthFlorida

    WorthFlorida The wife is still training me.

    Oct 28, 2009
    Orlando, Florida
    I hope you were referencing ebay as reference only. You probably cannot buy the AC unit since you need a EPA license because of the R410A. Your HVAC contractor would have to buy it. The NY company reads a wholesale supplier so it might means they bought some old stock from a fire sale or auction of a business that went under. If they do sell it they could be subject to EPA fines.
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  4. Stuff

    Stuff Well-Known Member

    Mar 7, 2013
    You need to find a someone you trust to figure out what size system you need and don't worry too much about brands. Article below is a good read discussing this point. With most home projects they recommend that you get three quotes. With HVAC you may need to get ten or more before you find someone who is willing to spend the time to get the right system for you. The calculation to find what size systems you need for your house is called a Manual J. It takes hours to do correctly and even then requires guesses (how tightly sealed, R value, etc.) that can easily skew the results. After that there are other calculations to verify your duct sizes and more.

    Unless you are going to do all of the install yourself you should let the installer buy the equipment. One argument is that you don't take a bag of groceries into a restaurant and expect the chef to make you a meal with it. Another argument is that you want the installer to handle all warranty work, parts and labor.

    Also, the regulations around 410a are really screwy. It is legal to buy/sell in the US without any license or certification. EPA's site currently says that beginning in 2018 technicians will need certification to work with it. R-22 is the old stuff that requires certification for all including removing and disposing of your old equipment.
  5. Dana

    Dana In the trades

    Jan 14, 2009
    Your systems are ridiculously oversized for both heating & cooling loads. A typical 2000' house with double-panes, R11 in the walls and R19 in the attic will have a space heating load of about 20,000 BTU/hr @ 35F, often less (depending on air leakage). Concord's 99% & 1% outside design temps are +38F and 97F, accrodingly, and the latent cooling loads are negative. Depending on how much west facing glass you have your cooling load is likely to be less than 24,000 BTU/hr, could easily come in under 18,000 BTU/hr.

    Since the prior system was a gas burner, it's possible to determine an upper bound for the heat load based on the fuel used by the old system against weather data for some wintertime gas billing periods, effectively using the furnace as the measuring instrument.

    Seriously, unless you have an aggressive Manual-J heat load calculation showing a much higher load, it would be crazy to install a heat pump bigger than 2-tons. If you want to take a stab at a Manual-J, try this tool. Use the most aggressive rather than conservative assumptions on R-values, etc., since the step sizing of equipment will always cover the margins in the rare instances where the assumptions are too aggressive. The biggest question mark is usually air infiltration, and if you underestimate your air leakage you can usually gain both comfort & efficiency by tightening the place up with a pass of blower-door directed air sealing. (Which is nearly always cost-effective on energy cost savings, at least on the first pass.)

    Any ducts in the attic, above the insulation we need to know about?
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