Home Heat Loss Calculator

This calculator will provide an estimate of the heat loss for your home, including:

- Maximum heat loss in BTU/hr for a coldest day (helpful for furnace sizing)
- Total yearly heat loss in millions of BTU.
- Total yearly cost for fuel.
- Total ten year cost for fuel (with 10% fuel price inflation per year).
- Pounds of CO2 gas emissions for heating your house.

A few changes have been made to the calculator - details...

 

Please note these important sources of error.

To use the Heat Loss Calculator:      

Fill in all the input boxes.
(the light blue boxes)		 input button Then, click on the button below that looks like this  When you click "Calculate", the output cells will be calculated and displayed.  You must click the Calculate button to see the effect of any changes you make. 

Examples and Usage Information

Worked examples here.   

Help on R values...   If you are starting with no insulation, read this carefully... 

Handling crawl spaces ... 

Handling slabs... 

Help on Heating Degree Day estimates...

Design Temperature and Fuel Type Inputs
Title
Design outdoor Temperature Degrees F Coldest temperature expected in a "normal" year   more... 
Heating Degree Days Degree F - day Heating Degree Days   more...
Natural Gas
Fuel Oil
Propane
Electricity
 Furnace Efficiency (%) more...
Area and Rvalue Inputs
Ceilings
Ceilings --- Enter the area and R value for each ceiling area in the house that is exposed to outside temperatures.     Help on R values ...
Area
(sqft)		 Rvalue UA
(BTU/hr-F)		 Design Loss
(BTU/hr)		 Yearly Heat Loss (million BTU/yr)
Ceiling 1
Ceiling 2
Ceiling 3
Ceiling 4
Walls  Enter the area and R value for each wall area in the house that is exposed to outside temperatures.  Do not include window and door area.
Area
(sqft) 		Rvalue UA
(BTU/hr-F) 		Design Loss
(BTU/hr) 		Yearly Heat Loss (million BTU/yr)
wall 1
wall 2
wall 3
wall 4
Windows &
Doors		 Enter the area and R value for each group of windows or doors having the same R value.
(U = 1/R, so a window listed with a U of 0.33 has an R value of 3)
Area
(sqft) 		Rvalue UA
(BTU/hr-F) 		Design Loss
(BTU/hr) 		Yearly Heat Loss (million BTU/yr)
Group 1
Group 2
Group 3
Group 4
Floors Floors - Wood Joist Type --- Enter the area and R value for each floor area in the house that is exposed to outside temperatures.  Estimating R Value for crawl spaces ...
Area
(sqft)		 Rvalue UA
(BTU/hr-F)		 Design Loss
(BTU/hr)		 Yearly Heat Loss (million BTU/yr)
Floor 1  
Floor 2
Floor 3
Floor 4
Slabs Slab on Grade Floors --- Heat loss from slab on grade floors is primarily dependent on the length of the perimeter and not the area of the floor. "Rvalue" here is the effective R value per foot of perimeter.  Estimating effective R Value for slabs ...
Perimeter (ft) Rvalue per ft of perimeter (1) UA
(BTU/hr-F)		 Design Loss
(BTU/hr)		 Yearly Heat Loss (million BTU/yr)
Full Slab
Infiltration House Volume is the total volume of the heated space of the house cubic feet (floor area times the ceiling height)
Typical Air Changes Per Hour:
     0.33 -- very tight -- minimum for health
     0.5 -- tight --  new, careful construction
     1.0 -- leaky -- typical existing construction??
House Volume
(cubic ft)		 Air Changes per hour UA
(BTU/hr-F)		 Design Loss
(BTU/hr)		 Yearly Heat Loss (million BTU/yr)
Whole House
Internal Heat Gains These are heat gains from warm bodies, lights, appliances, ...
This is heat that your furnace does not need to provide.
If you don't want to account for internal heat gains, enter 0 for the number of occupants
Number of Occupants   Internal Gains
(BTU/hr)		 Design Loss
(BTU/hr)		 Yearly Heat Loss (million BTU/yr)
 

Summary Outputs  (see table above for detail outputs)
Click to update Heat Loss results.
Item UA
(BTU/hr-F)		 Design Loss
(BTU/hr)		 Year Loss
(Million BTU/yr)		 Fuel Cost
(US dollars)		 Ten Year Cost
10% infla $''s		 Greenhouse
Gas (lb CO2)
Ceiling Loss
Wall Loss
Window Loss
Floor Loss
Slab Loss
Infiltration
Totals
Internal Gains Internal heat gains (warm bodies, lights, ...) supply some of the heat listed above -- the line below shows approximately the contribution of internal heat gains -- this is heat that your furnace does NOT have to supply.
  [Your browser does not support Plotting with HTML5 Canvas]  

This software is provided "as is" -- use at your own risk.  I am not responsible for any errors, inaccuracies or omissions in the software.  Under no circumstances am I liable for direct, indirect, special, incidental, or consequential damages resulting from the use, misuse, or inability to use this software, even if I have  been advised of the possibility of such damages -- Gary

 

Definitions of the Output Columns:

 

- Design Heat Loss  -- This is the total heat loss from your house per hour when the outside temperature is at the Design Outdoor Temperature that you input.  This can be used as a rough guide for sizing your furnace -- but see the discussion on Internal Gains above.  (BTU/hour)

 

- Year Heat Loss -- This is a rough estimate of the total heat loss from your house for a typical year.  It is based on the number of Heating Degree Days you entered.      (BTU/year)

 

- Fuel Cost  -- This is the cost of the fuel to heat your house based on the Year Heat Loss from the previous column, and the fuel type, fuel cost, and furnace efficiency you entered.  (Dollars)

 

- Ten Year Cost -- This is the cost of fuel for 10 years with the assumption that fuel costs will rise 10% each year of the 10 years.   (Dollars)

 

- Greenhouse Gas Emissions -- This is the yearly green house gas emissions from your heat plant.  It is based on the type of fuel you selected, the furnace efficiency you entered, the Year Heat Loss.  For electricity, it is assumed that the electricity was generated at an average US rate of 1.5 lbs CO2 per KWH.    (lbs of CO2 per year)

 

Note:

- You must have Javascript enabled in your browser to run this calculator (Tools -> Internet Options -> Security)
- For the Design Day heat loss calculation, the inside temperature is assumed to be 70F.
- Remember that you must click the Calculate button to see the effect of any changes you make to the inputs.


HINT: if you want to save the output use the Print function on your browser to either print it, or save it to a pdf, and sometimes other types of files. One way to access the Print function is to right click anywhere and select print off the right click menu. The right click menu on MS Explorer browser will also export the data to OneNote, which works well.

 

Updates:

Gary 5/5/07, 3/2/08, 12/18/2008
Updated: April 17, 2008 Clarified slab effective R value, added two examples.
Nov 7, 2009 Added some more help files
April 4, 2011 Fixed some formatting and nav menu issues
August 15, 2012 Added plot and title, many cleanups, formatted for better printing and clearer look.
December 3, 2012 added a few clarifications to the labels.