Manual J for Ducted Heat Pump / Air Handler System
I’m sizing a heat pump to install one the second floor of my house to replace the electric baseboard in each room. I got several outrageous quotes last spring (ducted $19k, ductless $17k) that didn’t include electrical hookup, drywall work, or plumbing (gas furnace, proposed ducted system was AC only and NG furnace). This was for a single zone system that only served the second floor. Decided to start planning it out and I’ll do the install myself in the spring. I’m a mechanical engineer by schooling and trade and I regularly work with AHJs and am intimately familiar with permitting. I’d consider my DIY skills well above average. Hardest part will be finding a local HVAC company to come run the lines and charge them with refrigerant.
Ducted heat pump with ducts and air handler in the attic looking at Mitsubishi and fujitsu. Anyways, long story short I’m doing my Manual J and S now and I have some questions on the Manual J as my cooling load seems very high compared to my heating load (or maybe my heating load is too low). Second floor is currently cooled with a 10kBTU window unit in the master bedroom and 5000-6000BTU window units in the remaining bedrooms. ~25kBTU of cooling overall
I thought NJ leaned towards a heating dominant climate. The internal loads seem a bit high.
– R11 2×4 walls average air tightness 1976 construction no renovations
– first floor is slab on grade no insulation on slab. 42kBTU pellet stove for heat (1-2 bags of pellets a day when it’s below 32deg). No AC on 1st floor, stays very cool in the summer, hottest I’ve seen it get is about 78 degrees.
– low E rated windows with the sticker still on them appear to be circa 2000
– unconditioned attic with ~R22 insulation in rafters
– 2nd floor is 4 bedrooms and 2 bathrooms
– 5 occupants in respective bedrooms
– ceiling fan, TV, and light fixtures in each bedroom
– I will be installing R8 (or higher if I can) ducts in attic, extremely airtight (need to pass pressure test per IECC)
– default design temps
Do these internal loads seem high and cooling load seem high, or conversely is my heating load too low? I’d appreciate any input or suggestions, posted this on Reddit as well with no luck. It looks like given the latent load I will need a 2T Mitsubishi hyper heat.
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