I have a couple questions which I would really appreciate some help on. I am in the process of selecting a HVAC contractor to install a new heat pump in my 48’ x 28’ bilevel home in eastern PA (about 1700 SF living space). Home needs everything (outdoor unit, indoor unit, ductwork, etc.) as the current source of heat is a kerosene monitor heater (draws outside combustion air into a sealed chamber and exhausts combustion products exterior to house….great system but with oil prices you know the story) and electric baseboard (which is rarely if ever used). The downstairs portion of the house will not have a supply register but will have one return sized to be able to pull 90% of required return off the lower level ceiling so I can move the warmed area from the lower level through the duct system and disperse it upstairs when the temperatures drop below about 15 –20 degrees. There is a transfer grill between the upstairs and downstairs that will permit air flow to the lower level. The upstairs will have one central return. The downstairs and upstairs returns will be dampered by some means so I can pull 90% of the return air from either the upstairs or downstairs depending on the season.
My questions are as follows:
1. Unit was going to be American Standard 14 SEER unit with a variable speed airhandler……details are TWE031E13FB variable speed airhandler, 2A6H4030A1000A outdoor unit and a ACONT802A532D t-stat. Is there any advantage of going to a TWE037E13FB airhandler (which is slightly larger unit) instead? Both airhandlers are listed for the 2.5 ton compressor, but the TWE037 is a tad larger. What will be gained and is it worth the $150 more contractor wants for the TWE037 unit?
2. Registers….should registers be “across the ceiling blows” or “downward blows”? I keep hearing differing opinions on the type of register that should be used and I gotta admit am confused on the pros/cons for each for such a seemingly simply part of the system.
3. Ductwork….everything is going to be R-8 insulated, but am having a hard time deciding in the cost of a metal trunk system with short flex duct runs vs. a metal extended plenum system with much longer flex duct runs. I am worried that the metal trunk system will be more apt to leak due to poor install, but am also worried that an extended plenum (contractor says about 5-foot plenum) is not the way to go due to a couple of the flex runs probably requiring 25-foot runs. Is there really anything wrong with using longer flex duct runs?
Thanks for any comments in advance.
hope this helps...
2.) Registers on dual season units should be "downward blowing" over infiltration points (ie. windows) if only because the other type will keep the heat only at the ceiling. "Across the ceiling" registers, or diffusers, are best on cooling-only systems, IMO.
3.)Either system can be done and working proper with a close eye paid to sizing the duct runs. All else being equal (read: CFM) flex duct needs to be upsized per Manual D, properly suspended and run to mitigate against excessive constriction and of course properly spliced to prevent leakage. Metal ductwork must be be sealed at all joints, slips/drives, and take-offs with an approved duct mastic. A qualified contractor will know this. Use balancing dampers on all supply runs.
Regarding your point about dampering the returns--it's essential to size each one to accomadate all the return air independent of the other, then take into account the TEV to include a damper so as to avoid noise and excessive friction. Perhaps this is obvious ... Best of luck and I leave question # 1 to the Amer Stand. dealers out there.
PS...Invest in a good filtration system ...