Heres a Link: http://www.greenbuildingadvisor.com/blogs/dept/musings/saving-energy-manual-j-and-manual-d Even when they do the calculations, the results are usually wrong In his posted comment, Bailes raised an interesting point: the problem of “garbage in, garbage out” (GIGO) Manual J calculations. Several energy experts have commented on the GIGO problem, including John Proctor, Hank Rutkowski, and Allison Bailes. Hank Rutkowski, the mechanical engineer who wrote the original Manual J document, was recently interviewed for a profile posted on the Green Building Talk Web site. The piece notes, “Rutkowski estimates that only 10% of heating and cooling equipment sizing decisions are based on some type of Manual J calculation and that less than 1% of the jobs are based on an aggressive implementation of the recommended design procedures.” Rutkowski explains the GIGO problem this way: “Manual J is a good tool if you use it aggressively. Follow the rules and it will give you a reasonable margin of safety. But the average contractor says, ‘Better safe than sorry,’ so he fudges here and there. He adds 5 to 10 degrees to the summer and winter design temperatures, calls the building ‘average’ instead of ‘tight’ and doesn't take credit for shading by interior blinds and drapes. Then when he finally comes up with a load number for sizing, he throws in an extra half-ton of AC just for the heck of it.” For a high-performance home, sizing by Manual J may still result in oversizing Several years ago, I had a conversation with building scientist Joe Lstiburek about air conditioners installed in Building America homes in Las Vegas. “HVAC designers are committed to the institutional oversizing of air conditioning equipment,” Lstiburek told me. “The average system is sized at 150% to 200% of the requirements of Manual J. They oversize because they don’t know what they will get for a building envelope, and to compensate for duct leakage and inappropriate refrigerant charge. If you size according to Manual J, there is already a fudge factor built in. But most designers then add another fudge factor.” According to Lstiburek, their experience proved the high-performance Building America homes in Las Vegas could have had HVAC systems sized at about 60% of Manual J. To be conservative, his team recommended installing systems sized at 80% of Manual J. Does oversizing matter? There are strong arguments against routine oversizing of HVAC equipment. The best argument is simple: oversized equipment usually costs more than right-sized equipment. Oversized equipment suffers from short cycling. For example, an oversized furnace brings a home up to temperature quickly, and then shuts off. A few minutes later, it comes on again, only to shut off quickly. Many homeowners find the see-saw sound of a short-cycling furnace to be annoying. When air conditioners short cycle, the units don't run long enough to achieve much dehumidification ��" at least in theory. (During the first few minutes of operation, an air conditioner cools a house. But not enough moisture has collected on the cold coil or on the pan below for any water to have actually gone down the drain. When the air conditioner turns off, all of the moisture in the pan and on the coil just re-evaporates.) The conventional wisdom may be wrong, however Increasing evidence shows that energy experts have exaggerated the negative effects of equipment oversizing, however. Studies have confirmed that oversized furnaces don't use any more energy than right-sized furnaces. Moreover, newer modulating or two-speed furnaces operate efficiently under part-load conditions, solving any possible problems from furnace oversizing. Although there are ample reasons to believe that oversized air conditioners are less effective than right-sized equipment at dehumidification, at least one field study was unable to measure any performance improvements or energy savings after replacing an existing oversized air conditioner with a new right-sized unit. The bottom line The main reason to choose right-sized equipment is to avoid paying too much money for equipment you don't need. A Manual J calculation will ensure you don't spend more than necessary for your furnace, boiler, or air conditioner. Moreover, a Manual J calculation will provide room-by-room heat loss and heat-gain information that is essential to good duct design. Without good duct design, you're running the risk of comfort complaints.

Did you have a 5-ton unit before? Ask the dealer to do a load calculation to determine sizing before you sign the quote. That's a lot of money to be spending and you wouldn't want to be getting an oversized system. Also have the dealer check the ductwork for sizing and ample supply and return. No system will work well and deliver its full capacity with a bad, undersized ductwork system. You are being quoted for a HEAT PUMP, which I would recommend. It can heat and cool. The 24ANA7 and 24ANA1 are air conditioners. The main difference between the 16/17 SEER and 19/21 SEER models are the compressors. I suggest the lower-SEER models for the better staging between the two stages. The 16/17 SEER models have a bigger difference in capacity between stages allowing for a longer run time and better dehumidification. Also, I say XX SEER "models"--a lot of it is marketing. Not all matchups will get those SEER ratings. The Carrier Infinity system is a very nice system, and in Florida I think you'll see many advantages from it from a comfort and efficiency standpoint. Whether or not you want to replace just the compressor to buy you a few more years is up to you. They usually don't carry long warranties. The matchup you were quoted gets 15.3 SEER. See above regarding SEER ratings. Don't believe the 19 or 21 SEER claims--they aren't true for all matchups. A 5-ton unit can't achieve the higher SEER ratings as easily. The 19 SEER unit would buy you a lousy .2 SEER, so 15.5 SEER. The Air Conditioning and Refrigerant Institute rated this matchup. Reference number - 1250425.

The two equipments are in the attic. Each unit has 2 returns, one 16 and one 10'. Three return are upstairs on the walkway, and one, the 10' in the MBR downstairs. A new return could b easily added upstairs (above the main door (at 21 ft high) and also with more work and costs downstairs in the master bathroom, in the closet or in the studio. Our MBR is cold in winter since furthest away from unit and (probably) short on supply. One new supply duct of 8' (with new grill) will be added to the other 2. The problem is that from the furnace one 14' delivers air to the east side of the house to 8 grills...apparently this is too much. The downstairs unit has on the supply side a 8, a 10 and a 14' duct; a 16' and a 10' on the return side. What do you thing, is it a valid and correct option to increase the 16' return to a 18' and to add a new 8' supply to the plenum for the MBR or what would you do? I would like to do it the right way and to fix what can be fixed only one time. None of the 9 contractors I got could convince me with a solid knowledge, unfortunately! Thank you!

Maybe I was generous. At 10 FPS, inch and a half pipe will do between 60 and 65 GPM. Todays recommended maximum FPS is 10 on the return and 8 on the suction. These numbers are based on safety and friction loss.You can push higher volumes of water through but your friction loss will increase very quickly. A 1.5 HP Super Pump will exceed these velocities. If I was generous, the reduced flow numbers would dictate an even longer run time for his pump, increase his power consumption, shorten his motor life, etc... only adds to the benefit of having the high efficiency motor of an Intelliflo with it's ability to be dialed down to both reduce power consumption and reduce friction loss by running slower.