Greenhouse Heat Loss Calculations: 7 steps. Step 1. List greenhouse dimensions in feet: Wall height, A= House width, B= House length, C= Rafter length, D= Lower wall height, E= Upper wall height F= Gable height, G or H= Step 2. Calculate the appropriate surface areas and perimeter. N is the number if individual house sections forming each greenhouse range. N= 1 for a single house. Lower wall area: 2N(E x B) + (E x 2C) = Upper wall area: 2N(F x B) + (F x 2C) = Single material wall: 2N(A x B) + (A x 2C) = Gable area: N x B x G = Curved end area: 1.3N x B x H = Gable roof area: 2N x D x C = Curved roof area: N x D x C = Perimeter: 2 [(N x B) + C] = Step 3. List construction materials and U factors for each surface. Table of Heat Transfer Coefficients (U-Factors): http://www.oznet.ksu.edu/dp_hfrr/Floriculture/index2.htm Location Construction material U Factor Lower wall U1= Upper wall U2= Single material wall U3= End Area U4= Roof U5= Perimeter U6= Step 4. Calculate appropriate conduction heat loss, hc. hc = Area x U x .T T = Inside night temperature - minimum outside temperature Lower wall area x U1 x .T = Upper wall area x U2 x .T = Single wall area x U3 x .T = Gable or curved end area x U4 x .T = Roof area x U5 x .T = Perimeter length x U6 x .T = Total = QC = Step 5. Calculate greenhouse volume. Gable house volume: N [(A x B x C) + (B x G x C/2)] = Single curved roof house volume: 2H x B x C/3 = Multiple curved roof volume: N[(A x B x C) + (2H x B x C/3)] = Step 6. Calculate air infiltration losses, hinf. Table of Air Infiltration in Greenhouses: http://www.oznet.ksu.edu/dp_hfrr/Floriculture/index2.htm hinf = 0.02 x .T x Volume x Air exchanges/hour = Step 7. Calculate total heat loss, ht. ht = hc + hinf = Source: Greenhouse Engineering, 3rd ed. 1994. By R.A. Aldrich and J.W. Bartok. Northeast Regional Agricultural Engineering Service (NRAES-33).     .