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Old 02-23-15, 07:59 PM   #1
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Default How To Make a Graph of Your Heating Degree Days

I have used the information from Heating & Cooling Degree Days - Free Worldwide Data Calculation for various things, and graphing heating degree days for my local area has proven to be surprisingly insightful.

Here's how I have done it...

1. Go to Heating & Cooling Degree Days - Free Worldwide Data Calculation

2. Find a station that is recording weather data in your area. For this example, I am assuming that my zip code is 97214. So I enter 97214 in the box labeled "Sation Search". Then I click the 'Station Search' button. In this case, I see about 40 stations in my target area. Many of the stations indicate how far they are away (the program assumes the distance from the 'center' of the zip code area, your distance my be different). If I want to really zero in, I can go to 'Google Map' and enter the Longitude/ Latitude information, by removing the comma and leaving a space. Some stations may be topographically influenced, so make your best guess.

3. For this example, I want to know the average monthly degree days in my area. I'd like to get a 5 year average, but I may have to settle for less. Next, Click on the Generate Degree Days Button. If you station has that data, it wil be returned to you within a few seconds. You may have to try other stations to get your results. I had to settle for one year... Here's what I got in my example:

Description:,"Fahrenheit-based heating degree days for a base temperature of 65F"
Source:," (using temperature data from"
Accuracy:,"No problems detected"
Station:,"Stripling Weather Network - Richmond, Portland, OR, US (122.64W,45.51N)"
Station ID:,"KORPORTL230"

Month starting,HDD
4. Next, you can cut and paste the relevant data into a spreadsheet. If you don't have a spreadsheet, you can get an excellent one called Gnumeric (FREE, opensource, no crapware), that' s my personal choice.

It looks like so:

5. If you use your mouse and drag over the block of relevant data, and then click the colored bar icon that is just barely visible to the upper right-most edge in the image above... you have a choice of graphs at your disposal.

This is a small line graph, but there are pie charts, and bar charts galore.

6. Here is a graph done not with monthly data, but with daily data, over the same time period:

Of great interest is that in this particular weather locale, there is considerable temperature variation, especially in the coldest months. This would imply that a high-mass heating structures, like a thick cement slab radiant floor, could have a real problem responding to sudden variations in weather. Of course, in areas where it gets cold and stays cold, this would not be a problem. So much depends on location.

7. There are also some interesting numerical uses of Heating Degree data. For this example, I'm going to see what percentage each month's Heating Degree Day is compaired to the whole year. First I'll sum up the month's HDD.

Then I'll make a quick formula for the top cell (note that a cell that is a 'fixed cell' uses "$" in the designation.

Then I'll drag the formula down so that I see what's happening for each month.

I could use this to see what my monthly cost was for fuel oil, if I paid $1500 per year (I don't use the stuff, but maybe that's possible). So I could take the $1500 dollars and multiply it by percentage, and get a pretty good idea.

This method is overlooking the fact that all houses are a bit 'Passive House' and will naturally gain and retain heat, sometime for the better, sometimes 'not so much'.

Another way this could be used, would be to look at what a passive house annual heating allowance would look like for some house. For this example, I'll assume a floor area of 1000 sq. ft. = 92.90 square meters.

The passive house heating allowance is 15kWh annually per square meter, or in our case

Allowance = 15kWh x 92.90 = 1,393.5kWh per year.

If we were to look at that on a monthly basis, both in kWhr and cost (It's $0.11 where I live)...

This might actually be worth spending money on insulation!

....again this is just a rough estimate.



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I'm not an HVAC technician. In fact, I'm barely even a hacker...

Last edited by AC_Hacker; 02-25-15 at 12:57 AM..
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Old 02-24-15, 08:28 PM   #2
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Having purchased my first cold climate home last November, this post has given me a real estimating tool to work with. Thank you AC.
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Old 04-11-15, 01:38 PM   #3
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The default base temp of 65f is wrong for most people. 55f base temp is more accurate if you keep your heat set between 65f-70f and have a reasonably well insulated house.

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