Home Heat Loss Calculator

This calculator will provide an estimate of the heat loss for your home.

It estimates the following:

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

Please note these important sources of error.

 

To use the Heat Loss Calculator:      

Fill in all the input boxes.  They look like this  -->
(medium blue backgrounds)		  
When you have filled in all the inputs, click the "Calculate" button.   It looks like this      ------>  

When you click "Calculate", the output cells will be calculated and displayed.  Note that any time you change an input, you must hit "Calculate" again to update the results.  There are links to help files in the form to explain the inputs, and provide some help in figuring out what to enter for your situation.

Examples and Usage Information

There are a couple of 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 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...
Ceilings Enter the area and R value for each ceiling area in the house that is exposed to outside temperatures.
Help on R values ...
Ceilings Area Rvalue UA (BTU/hr-F) Design Loss
(BTU/hr)		 Yearly Heat Loss (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.
Wall segment Area Rvalue UA (BTU/hr-F) Design Loss
(BTU/hr)		 Yearly Heat Loss (BTU/yr)
wall 1   
wall 2   
wall 3   
wall 4   
Windows Enter the area and R value for each group of windows having the same R value.
Window Group Area Rvalue UA (BTU/hr-F) Design Loss
(BTU/hr)		 Yearly Heat Loss (BTU/yr)
Group 1
Group 2
Group 3
Group 4
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 ...
Floor segment Area Rvalue UA (BTU/hr-F) Design Loss
(BTU/hr)		 Yearly Heat Loss (BTU/yr)
Floor 1  
Floor 2
Floor 3
Floor 4
Slab on Grade Floor Heat loss from slab on grade floors is primarily dependant 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 ...
Slab segment Perimeter (ft) Rvalue per ft of perimeter (1) UA (BTU/hr-F) Design Loss
(BTU/hr)		 Yearly Heat Loss (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)
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 Air Changes per hour UA (BTU/hr-F) Design Loss
(BTU/hr)		 Yearly Heat Loss (BTU/yr)
Whole House
Internal Heat Gains These are heat gains from warm bodies, lights, appliances, ...
These heat gains will be subtracted from the total heat loss for the house.
If you don't want to account for internal heat gains, enter 0 for the number of occupants
More ...
  Number of Occupants   Internal Gains
(BTU/hr)		 Design Loss
(BTU/hr)		 Yearly Heat Loss (BTU/yr)
 
  Click Calculate to update Heat Loss
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 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.
Internal Gains
Print page...

 

 

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.     For the reasons discussed here, it may be somewhat more than what you actually experience.  (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.  For the reasons discussed here, it may be somewhat more than what you actually experience.  (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.  For the reasons discussed here, it may be somewhat more than what you actually experience.  (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 a coal fired power plant -- about 50% and increasing of electricity in the US is produced in coal fired power plants.  For the reasons discussed here, it may be somewhat more than what you actually experience.  (lbs of CO2 per year)

 

Note: You must have Javascript enabled in your browser to run this calculator (Tools -> Internet Options -> Security)

 

Please Note 

I take no responsibility whatever for the accuracy or correctness of this software.

I take no responsibility whatever for any grief that errors, omissions, or just plain bad design in this software may cause you.  

You use this software at your own risk.

 

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 formating and nav menu issues