The flame is in the same air as the cones
You are drying hops in the Willamette Valley, and the burner is the machine that can ruin the lot before the baler starts. Oregon harvested 5,354 hop acres in 2025, second among the three states USDA reports, at 1,759 pounds per acre[1]. The cones on those acres are an aroma crop. A direct-fired kiln does not have a heat exchanger between the fire and the bed. If the fire is rich, the bed sees it.
- Aroma practice in the OSU kilning research sits near 125 to 135°F, not the older 140 to 155°F band.
- DEQ’s permit line is a heat-input test, not a substitute for looking at the flame.
- This path is not a Marion County farm-crop dryer and not a steam boiler.
The rule on this valley floor
Two documents govern two different risks. The product risk is temperature and combustion quality. Lindsey Rubottom’s Oregon State University dissertation describes the industry move from drying near 140 to 155°F in the alpha-hop years to about 125 to 135°F once aroma varieties dominated, on the view that lower temperature would hold volatile oils[2]. That is a research record of practice, not a DEQ setpoint. Treat it as the band your aroma lot is probably supposed to see, and confirm it against the grower’s own specification.
The permit risk is heat input. Oregon DEQ requires a permit for sources on OAR 340-216-8010 Table 1. Gas and propane boilers of at least 10 and less than 30 MMBtu per hour, built after 9 June 1989, are the Basic Permit 04 group, unless diesel backup exceeds the small-tank limit. Oil-fired equipment over 10 MMBtu per hour, and gas, propane, or butane at 30 MMBtu per hour or more, fall toward General Permit 11[3]. A kiln burner is “other fuel burning equipment” in that table’s logic only when it meets the rating. Read the plate. Do not guess from the size of the building.
NFPA 86 (2023) defines combustion air as the air necessary for complete combustion, and a Class A furnace as one that heats combustible material[4]. Hop cones are combustible crop. Whether your building official is enforcing that standard is a question for the official. The Building Codes Division’s adopted-codes list names the 2025 Mechanical Specialty Code, mandatory 1 April 2026, and does not on that page name an ovens code[5]. Say what you observed. Do not claim a code adoption the division page does not print.
If you skip the retune
You skip it and the bed keeps moving, because harvest does not wait. Incomplete combustion leaves soot and odor in the only air the cones will see for the next several hours. The OSU work also spent years on wildfire smoke in kilns, which is a different contaminant with the same lesson: the drying step is when the cones are a filter. A rich burner is not wildfire, and this page does not pretend the dissertation measured your nozzle. It does say the air touches the product.
If the burner is large enough for Table 1 and you operate without the permit, you are outside the DEQ requirement that listed sources obtain one[3]. This page does not print a penalty dollar, because the permit page used here does not print one. The operational loss is the lot, plus a file that is open when an inspector asks.
Who signs, who pays, how long
| Step | Who signs | Clock |
|---|---|---|
| Air permit, if the rating is on Table 1 | Owner or operator, to DEQ | Before operating a listed source |
| Flame observation and retune | The person you authorize on the callback | Before the next bed, not after the bale |
| Steam vessel, if you have one | Equipment owner holds the operating permit | Before the vessel is placed in operation |
| Kiln diagnostic price | No published statewide fee | Verify — this table will not invent one |
Why Marion County is a different URL
Marion County’s rural zoning chapter lists facilities for processing farm crops as a use. It does not publish a stack limit, and it is not a hop-kiln specification. Lane County’s air permits go to LRAPA, which says businesses outside Lane County go to DEQ. A sentence about cone temperature and Citra acreage becomes false if you paste it onto a Marion dehydrator. The dehydrator note is the neighbor, not a second copy of this page.
| Question | Willamette hop kiln | Marion farm-crop dryer |
|---|---|---|
| Product in the air | Hop cones for aroma | A farm crop under the county processing use |
| Temperature evidence | OSU aroma band, about 125 to 135°F | Not that dissertation |
| Air agency | DEQ if Table 1 applies | DEQ, not LRAPA |
| Vessel stamp | Only if a separate boiler exists | Same split |
Checklist for this kiln
- Confirm the kiln is direct-fired, so combustion products meet the bed.
- Read bed temperature against the aroma band, then against your own lot spec.
- Look at the flame. A sooting orange fire is incomplete combustion.
- Read the heat-input plate against the 10 and 30 MMBtu lines before you talk permits.
- Keep any steam boiler on its own permit file.
- Do not use a Marion dryer procedure, a Bull Run water log, or a Bend pump curve on this bed.
Fee and timeline
No Oregon document reviewed for this note publishes a price to diagnose a hop-kiln burner. ORS 480.595 and form 2502c publish vessel fees, and those fees apply to a boiler or pressure vessel, not to a cone dryer that never holds steam. If someone quotes you a permit fee for the kiln, ask which table it came from. Harvest timing is agronomic: the USDA report is an annual production document, not a calendar that says your ranch kilns on a named Tuesday. Plan the callback before the beds are already hot.
| Charge | Amount | Applies to the kiln? |
|---|---|---|
| Kiln burner diagnostic | Not published | Unknown until the contractor prices it |
| Boiler installation | $175, or $196 on form 2502c | Only if a vessel is in the scope |
| DEQ ACDP invoice | Not printed on the permit page used here | Ask the regional office if Table 1 applies |
Questions a manager actually types
Q1. What drying temperature are aroma hops actually run at?
An Oregon State University dissertation on kilning records the older alpha-hop practice at about 140 to 155°F, and the later aroma practice at about 125 to 135°F. The shift was made to protect volatile aroma, not because a statute set the setpoint. If your kiln is still on the older band while the lot is Citra or Mosaic, the burner may be “in flame” and still wrong for the cones.
Q2. Does a rich flame contaminate the bed?
NFPA 86 defines combustion air as the air required for complete combustion. In a direct-fired dryer the products of that combustion are in the process air. A lazy, sooting flame is incomplete combustion in the same stream as the cones. The standard does not print a hop-oil limit. It does tell you that complete combustion is the point of the air supply. Stop and retune before you blame the variety.
Q3. When does this burner need a DEQ permit?
When the source is on Table 1 of OAR 340-216-8010. DEQ’s boiler page places gas and propane equipment from 10 MMBtu per hour up to, but not including, 30 into Basic Permit 04 if it was built after 9 June 1989, with diesel backup under 10,000 gallons a year. Oil over 10 MMBtu per hour, or gas at 30 and above, is the General Permit 11 conversation. Below those lines you can still have a bad flame and no air permit.
Q4. Is the kiln a boiler because it has a burner?
No. A boiler is a vessel that heats water or steam and, if it is not exempt, needs an Oregon operating permit before it runs. A hop kiln heats air through a bed of cones. If the farm also has a steam boiler for another process, that vessel is a separate file. Do not hand the kiln nameplate to the vessel inspector and call the day finished.
Q5. How large is the Oregon crop this kiln is drying?
The 19 December 2025 USDA hop report lists 5,354 Oregon acres harvested, 1,759 pounds per acre, and 9.418 million pounds. Washington was 31,198 acres and Idaho 5,102, so Oregon is second in that three-state table. The report is statewide. It does not print a Willamette Valley subtotal, and this page does not invent one. Commercial Oregon hops are a valley crop, which is why the path is the valley and not a town.
Related
The statewide split among kiln, boiler, and pump is on the rule.
References
Accessed 9 October 2026 unless a page prints a later date.
- USDA NASS. “National Hop Report.” 19 December 2025. nass.usda.gov.
- Rubottom, Lindsey N. Dissertation, Oregon State University, kilning-temperature discussion. ir.library.oregonstate.edu.
- Oregon DEQ. Basic and General ACDP permits, boilers. oregon.gov/deq.
- NFPA 86 (2023), combustion air and Class A furnace definitions. nfpa.org.
- Oregon Building Codes Division. Adopted codes online. oregon.gov/bcd.