I had a previous question, debating value of double wall construction on our design.  However, I’m wondering if my calculations are good enough, so I’m trying to locate an Energy Advisor in Eastern Canada, and striking out.  I’ve contacted a few, but they’re not taking any new inquiries or customers!   Not clear if it was busy, or lack of staff.  If anyone has suggestions, please let me know.

My goal is to ensure my rough calculations put me in the ball-park for the final decisions required.  I have everything in CAD, and have all surface areas computed, along with HDD18C and Design Temp for the location.  To date, I’ve been using the calculator on the website BuiltItSolar, noting the site highlights the values are on the high side.  But is it 10%?20%?30 % or more?

It’s computing 48,900 Design BTU Loss/hr with the following parameters.

Design Temp -5F
HDD18C using 4,000 (location is closer to 3,900)
2,300 sqft Foundation – Slab On-Grade with 48″ frost wall
800 sqft Bonus room over garage 
3,975 sqft of wall
Average ceiling Ht  11′
3,100 sqft of flat ceiling
440 sqft of windows
144 sqft of doors (I’m adding this in the window field of the loss calculation)
270′ perimeter
32,000 cubic foot volume

Insulation
Ceiling – R60
Walls – R20+7.5ci (eff R-24)
Windows – R3.5
Floor Above Garage – R32
Under Slab – R12.5
Air Changes – 0.5  (WAG, but target is <1.0 ACH@50)

Air Source Heat Pump – Using COP of 2.5

Breakdown of the Losses are;

Ceiling Loss – 3,750
Wall Loss – 12,425
Window Loss – 12,539
Floor Loss – 1,641
Slab Loss – 4,050
Infiltration – 17,280
Reduction for 3 people (2,900)

Does the Heat Loss seem realistic or high given the parameters?  Switching to a double wall made little difference in the Wall Loss, and why I’m preparing to forego the cost.  Just want to make sure I’m not messing up the numbers above.