Normalizing EPA Data for better comparison

[Brian_L]

Being a total data nerd - as I was going through the EPA database, it was driving me nuts that some stoves are measured using cribwood, some using cordwood. So I set out to put together a spreadsheet to normalize the data. Here is a link to the google sheet I put together - you have to copy it to be able to change any of the inputs, but would love your feedback:

• Wood Room Heater Normalization Sheet

As far as methodology, here's what I did:

• According to the EPA methdology:
  • Cord Wood is measured by using 12 lbs of wood per cubic foot of firebox volume.
  • Crib Wood is measured by using 7 lbs of wood per cubit foot of firebox volume.
• While cord wood is no longer a valid measuring method, lots of stoves still have that data in it. Cord wood was tested at multiple levels of moisture, which makes comparison difficult and I suspect is why crib wood methodology is preferred for the measurement process going forward.
• I looked at a few different ovens that explicitly showed both cord and crib wood numbers to look at total heat output on low and high levels to come up with a "crib to cord" multiplier... the number I came up with was 1.29.
• EPA uses 6800 btu per lb of wood (both cord and crib) in their calculations

With this data, I calculated how much "cord fuel" was available taking firebox volume and multiplying it by 12lbs and then by 6,800 BTU/hr which gave total potential fuel; then multiplied that by the oven efficiency to give how much total heat is put into a room. Then, simply take the LHV/HHV numbers (straight up if cord wood, or multiplied by 1.29 if cribwood) and divided that by the total heat put into the room to get a "burn time" (yeah, it's not really burn time, I know). I also added a "target btu/hr" input at the top so ovens could be compared at specific output levels.

I'm sure this is not a perfect method, which is why I'd love to get folks feedback/input. What I did find interesting is that at 16K BTU target output (roughly what we'd estimate our need would be based on some heat load calculations I've put together based on some floor plans that I've been looking at), the following are the top 3 (in order):

1. Blaze King KE40, which comes out to 18.8 target burn time
2. Regency F5200 - 18.03
3. 44 Elite NextGen-Hybrid - 17.35

The top two are both wood stoves, with the 3rd being a wood burning flush mount fireplace, which is what my wife and I lean towards, aesthetically. I went through this whole exercise because (I'm OCD, of course) and wanted to better understand how much we're leaving on the table by prioritizing looks over functionality... which honestly doesn't look like much.

Brian

 

[BKVP]

Are you ready...

You must remember that the ASTM 3053 and M28R had different end points! That means a test was considered "over" when a cord wood tested unit hit 90% of the fuel load. The M28R stove tests were over when 100% of the fuel was consumed. May not seem like much until you look at the actual run data where a crib tested stove ran 20+ hours to get the the end and a cordwood tested unit was over in 8 hours.

This issue resulted in diluted BTU's and influences EVERY single metric from BTU's, efficiency, CO etc.

Sadly as it has become recognized, appliances from the two different methods cannot be compared in any manner.

Two stoves tested within the same method, that becomes a bit more possible, although the variability in the fuel density, amount of bark, variable m.c. range etc., make such comparisons challenging.

One further consideration, is ATM's. Yes, alternative test methods granted by EPA allowing the mfg's to seek approval to modify the test method in a specific manner. These would fall under cordwood tested, but the list does not show which were tested as ATM's and what changes were permitted to the method. ATM's are still being granted and are unit specific, not broadly applicable.

Comparing wood heaters is not easy. I have posted many, many times, what counts is dealer and customer satisfaction ratings with heaters. Like any stats guy, you can toss out the lowest lows and the highest highs and get to the truth.

Happy New Year!

BKVP