NSPS 2020 rule (Step 2)
The NSPS (New Source Performance Standards) for residential wood heaters is the EPA regulation capping particulate emissions from new stoves. Its “Step 2” limits, in force since May 2020, cap room heaters at 2.0 g/hr (2.5 g/hr cord-wood tested) — only compliant models may be manufactured or sold new in the US.
The 2015 rule introduced Step 1 limits (4.5 g/hr) and the 2020 Step 2 limits roughly halved them, also bringing forced-air furnaces and hydronic heaters under emission caps for the first time. That regulatory step is why the current certified list is dramatically cleaner than the installed base.
NSPS limits apply to manufacture and sale of new heaters, not to stoves already installed — an old stove remains legal to operate in most (not all) jurisdictions, though several states and air districts restrict or incentivize replacing pre-certification units.
| Step 2 effective date | 15 May 2020 |
|---|---|
| Room heaters | 2.0 g/hr crib wood; 2.5 g/hr cord wood (Step 1 was 4.5 g/hr) |
| Hydronic heaters | 0.10 lb/MMBtu heat output, weighted average, with no individual burn rate above 0.32 |
| Forced-air furnaces | 0.15 lb/MMBtu heat output |
| Codified at | 40 CFR Part 60, Subparts AAA (room heaters) and QQQQ (furnaces and hydronic heaters) |
| Certificate validity | Five years, renewable |
| Database today | 459 records; 198 currently certified |
What the rule covers — and what “EPA exempt” means now
The NSPS governs the manufacture and sale of new residential wood heaters. It does not regulate how you operate an appliance, and it does not make an installed stove illegal. Broadly, an appliance falls under the rule if it is an enclosed solid-fuel space or water heater with a firebox under about 20 cubic feet operating below roughly a 35:1 air-to-fuel ratio — the definition that historically separated “wood heaters” from other solid-fuel appliances.
Genuinely outside the rule are open masonry fireplaces, masonry heaters, wood cook stoves, outdoor fireplaces and fire pits, and certain industrial-scale appliances. Everything else that a homeowner would recognise as a stove is in scope.
That matters because “EPA exempt wood stove” used to be a real product category. Before 2015, single-burn-rate stoves and high air-to-fuel-ratio designs — barrel stoves, many shop heaters — could be sold without certification. The 2015 rule pulled single-burn-rate stoves, pellet stoves, forced-air furnaces, and hydronic heaters into the programme, so an exemption claim on a new indoor room heater today is almost always either an obsolete listing, an appliance that is genuinely not a room heater, or a seller hoping you will not check the database.
Step 1 to Step 2, and what it did to the market
Step 1 took effect in 2015 at 4.5 g/hr for room heaters. Step 2, from 15 May 2020, roughly halved that to 2.0 g/hr on crib wood and set a slightly looser 2.5 g/hr for stoves certified on cord wood, acknowledging that real firewood burns less predictably than lab cribs. For the appliances brought in for the first time, the caps are expressed per unit of heat delivered instead: 0.15 lb/MMBtu for forced-air furnaces and 0.10 lb/MMBtu weighted average for hydronic heaters.
The effect on the product range was severe, and the database shows it. Of 459 certification records, 198 are currently certified. Hydronic heaters took the heaviest hit — 34 of 167 records remain current — because 0.10 lb/MMBtu is very hard to hit with a boiler that idles, and forced-air furnaces are down to a handful of models.
The upside is that the current list is a genuinely different fleet from the installed base. Median certified emissions among current room heaters are about 1.5 g/hr, roughly a tenth of what an uncontrolled pre-1988 stove produces, and about a quarter of the fleet certifies at or below 1.0 g/hr.
What it means for a stove you already own or want to sell
Operating an older uncertified stove is legal in most of the US. What is often not legal is installing one, moving one to a new address, or selling one — a number of states and local air districts prohibit the resale or reinstallation of uncertified appliances, and some require removal or replacement at point of sale. Insurers and permit offices routinely ask for the certification label before signing off on an installation.
The financial angle usually runs the other way: change-out programmes in particulate-affected areas pay real money — commonly several hundred to a few thousand dollars — to scrap an old stove for a certified one, and they verify eligibility against this same database. Check your local air agency before buying, not after.
When reading a record, note that the applicable limit depends on the test fuel and appliance class, and that certificates expire after five years. A model listed as “previously certified” usually means nobody renewed the certificate — often because the model was discontinued — rather than that anything was found wrong with it.
Frequently asked questions
Is my old wood stove illegal?
In most of the US, no — the NSPS regulates manufacture and sale of new appliances, not the operation of one already installed. But several states and local air districts do restrict installing, relocating, or reselling uncertified stoves, and some require replacement at point of sale. Insurance and permit requirements can also effectively force the issue. Check your state air agency and local building department.
What is the EPA limit for a new wood stove?
2.0 grams of particulate per hour when certified on crib wood, or 2.5 g/hr on cord wood, for adjustable-burn-rate room heaters. Forced-air furnaces are capped at 0.15 lb/MMBtu of heat output and hydronic heaters at 0.10 lb/MMBtu weighted average. All of these have applied since 15 May 2020.
What is the difference between Step 1 and Step 2?
Step 1, from 2015, capped room heaters at 4.5 g/hr. Step 2, from May 2020, cut that to 2.0 g/hr (2.5 on cord wood) and applied the first-ever caps to forced-air furnaces and hydronic heaters. Step 1 units may no longer be manufactured. Only Step 2 compliant models appear on the current certified list.
Can I still buy a non-EPA wood stove?
Not as a new indoor room heater. Appliances genuinely outside the rule — open masonry fireplaces, masonry heaters, cook stoves, outdoor fire features — are still sold, but a new enclosed stove marketed as “EPA exempt” is a warning sign. The 2015 rule closed the single-burn-rate and high air-to-fuel-ratio loopholes that category relied on. Look the model up in the EPA database before buying.
Do pellet stoves have to be EPA certified?
Yes. Pellet stoves were brought under the NSPS by the 2015 rule and must meet the same 2.0 g/hr Step 2 limit as other room heaters. All seven currently certified pellet room heaters in the database sit between about 0.69 and 1.6 g/hr.