Does altitude affect AFUE? or just the input/output BTUs?

I searched and searched and searched yesterday for an answer to the question "Does altitude affect AFUE?" but did not come up with any definitive answers. Hopefully this discussion will answer that question more easily for folks in the future.

Derating combustion appliances typically applies the equation of about 2% per 1000 ft above sea level (from most manufacturer's specifications). So here in Santa Fe (at 7000 ft ASL), the derate would be 14%. Applying this to a 100 MBTUH input capacity appliance, the "natural" derating would make the appliance's input capacity actually 86 MBTUH. In all of the documentation I could find I could not determine if this derating ever affected the advertised AFUE or SSE rating, only the actual input/output in direct relation to the AFUE.

So my first question is, after an appliance has been naturally derated for altitude, can it be assumed to still function at the manufacturer's AFUE?

And then my second question is, assuming the above is true, and from what I have read here (http://hvac-talk.com/vbb/attachment.php?attachmentid=219042&d=1..., see appendix E), it would seem that Steady State Efficiency (and consequently, AFUE) actually improves with altitude. I know, right? Does anyone know at which rate the SSE (or AFUE) might improve with each 1000 ft increment above sea level?

Tags: AFUE, BTUH, Efficiency, SSE, State, Steady, altitude, derate, input

Views: 3026

Reply to This

Replies to This Discussion

Dale and I are referring to high efficiency condensing boilers designed to recover the latent heat of vaporization in a secondary heat exchanger designed for acidic condensate and capable of the highest combustion efficiency available in a gas-fired appliance. 

RSS

Forum Discussions

When is it too windy to use blower door?

Started by Brandon Walton in General Forum. Last reply by Kent Browning yesterday. 10 Replies

Electro Magnetic Fields (EMF)

Started by Barry L NewDelman in General Forum. Last reply by Arnie Katz on Thursday. 2 Replies

Affordable Housing Funding

Started by SUZETT MOFFITT in General Forum. Last reply by Diane Chojnowski on Wednesday. 4 Replies

Latest Activity

Profile IconEmily Rhea, Spray-on Foam and Keith Flores joined Home Energy Pros
yesterday
Kent Browning replied to Brandon Walton's discussion When is it too windy to use blower door?
"I found this post thru a Google search. I was already a member and have posted a few times. I am a…"
yesterday
Home Energy Magazine's video was featured

2017 U.S. Department of Energy Race to Zero Student Design Competition

The U.S. Department of Energy (DOE) Race to Zero Student Design Competition (Race to Zero) inspires collegiate students to become the next generation of buil...
yesterday
Dave Ransom joined James Sayers's group
Thumbnail

Marketing Energy Efficiency

Sharing ideas, tools and examples of promoting energy efficiency to consumersSee More
yesterday

Photos

Loading…
  • Add Photos
  • View All

© 2017   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service