Hi,
I recently purchased a house in Seattle with oil heat that we want to replace with a heat pump. ~1900 sq ft house built in 1939. It will be a dual zone system with a ducted air handler for the main floor and ceiling mini split for the finished basement. All ducts are in the conditioned space (in the attic ceiling). I have been getting various quotes with different system capacities and have also run my own manual j using cool calc.
As the house currently sits the most trustworthy installer calced at 53k btu since there is minimal insulation and I can match this with coolcalc. If I add r30 in the attic it drops to ~42k, r49 in the attic + r11 in the walls brings it to ~30k. I am sizing for heat as Seattle is dry in the summer and we get 10x more heat days than cooling days.
We have some remodeling projects in the plans so I don't want loose insulation in the attic right now. I am thinking of rolling out r30 and seeing if I can get someone to blow cellulose into the walls before next winter. I would follow up with r49-60 in the attic once we finish the projects in a few years.
Plan is mitsubishi hyper heat system so I don't need a second heat source. Discussion with the installer is between a 42k and 48k outdoor unit with 30+12 indoor. He is suggesting the larger and I am leaning smaller as it should be more efficient running closer to full capacity especially as I add more insulation. Another installer came up with 33k total but his tool doesn't allow for non insulated walls or attic so I am confident this is wrong. Getting one more quote next week as well.
Any thoughts?
I recently purchased a house in Seattle with oil heat that we want to replace with a heat pump. ~1900 sq ft house built in 1939. It will be a dual zone system with a ducted air handler for the main floor and ceiling mini split for the finished basement. All ducts are in the conditioned space (in the attic ceiling). I have been getting various quotes with different system capacities and have also run my own manual j using cool calc.
As the house currently sits the most trustworthy installer calced at 53k btu since there is minimal insulation and I can match this with coolcalc. If I add r30 in the attic it drops to ~42k, r49 in the attic + r11 in the walls brings it to ~30k. I am sizing for heat as Seattle is dry in the summer and we get 10x more heat days than cooling days.
We have some remodeling projects in the plans so I don't want loose insulation in the attic right now. I am thinking of rolling out r30 and seeing if I can get someone to blow cellulose into the walls before next winter. I would follow up with r49-60 in the attic once we finish the projects in a few years.
Plan is mitsubishi hyper heat system so I don't need a second heat source. Discussion with the installer is between a 42k and 48k outdoor unit with 30+12 indoor. He is suggesting the larger and I am leaning smaller as it should be more efficient running closer to full capacity especially as I add more insulation. Another installer came up with 33k total but his tool doesn't allow for non insulated walls or attic so I am confident this is wrong. Getting one more quote next week as well.
Any thoughts?
source https://hvac-talk.com/vbb/threads/2236150-Heat-pump-sizing-intput?goto=newpost
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