Short #31 - U-Factor and R-Value

HVAC School - For Techs, By Techs

Bryan Orr

Education, Business, Self-improvement, Careers

4.9 • 1K Ratings

🗓️ 27 November 2018

⏱️ 7 minutes

🔗️ Recording | iTunes | RSS

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Summary

What is the difference between r-value and u-factor? Why should we care about the differences? In this short podcast, we'll explain what those differences between the two are and why you should care.

R-value and u-factor are actually pretty close to the same thing; they are inverse coefficients of the same phenomenon. R-value is the resistance to heat energy moving through conductance. R-value is not concerned with radiant gains, such as the sun's UV rays passing through a window; the heat gains occur strictly through conduction, molecule-to-molecule, like heat passing from the wall insulation to the actual wall upon contact. In terms of insulation, a higher r-value is desirable, Inversely, we like to see a lower u-factor.

The u-value is the coefficient of heat transfer. So, the r-value's resistance to heat acts directly against the heat transfer of the u-factor. You can convert the u-factor to r-value by dividing the u-factor into 1 (1/u-factor). Similarly, you can get your u-factor from your r-value by dividing the r-value into 1 (1/r-value).

We use these values in load calculations and plug them into Manual J programs. We figure out our BTUs per hour in an equation where we multiply the square feet by the u-factor and the delta t. So, our insulation plays into equipment sizing. Some products also have a rated u-factor. You also need to average out the u-factors if you use multiple materials. (Note: sometimes, manufacturer u-factor ratings are not entirely accurate.)

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Transcript

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0:00.0	All right, so yes, this is a short episode of the H.E.C. School podcast, and actually today's
0:08.1	Thanksgiving. I'm sitting here in my home office and I wanted to get out a short
0:12.4	episode, so that way we'd keep the
0:14.6	schedule you gotta keep the schedule on radio the show must go on as they say
0:18.1	we've got 65 people coming over today at three and then we've got 45 coming tomorrow and my
0:25.2	wife is thrilled that I'm sitting here in my office talking to you in this short
0:27.9	podcast but it just shows how committed I am to you okay enough chit chat
0:30.5	because this is a short episode and first I've got to thank our sponsors
0:34.0	Navac and Navac Global.com carrier carrier.com air oasis at air oasis.com
0:40.1	forward slash go refrigeration technologies thank those guys for all of their
0:44.8	support and I also want to mention solder weld we're pleased to announce that the
0:49.7	Johnstone Ware Group in Central Florida has brought on some solderwell products for those of
0:55.3	you who are in Central Florida to try. So thank you to them. Thank you to Black Supply
0:59.2	also for doing that here in Central Florida. But if you are not able to find it on the shelves where you are right now
1:04.7	then I would suggest that you have your local supply house contact products by
1:09.7	pros products by pros.com in order to get Sodder Weld on the shelf, it's great stuff, you will love it.
1:15.8	Today's episode is on R value and U value, R value and U value.
1:21.2	And I think these are things that we tend to ignore in general as technicians
1:24.6	but if you're ever going to do a load calculation these can come up pretty quickly and I know
1:28.5	I was confused by it because some things have our values listed on them some have you values listed on them, some have U values listed on them,
1:33.6	and it gets really confusing.
1:34.6	But we're doing this class with Jack Rise
	...

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