A Propane Heater Guide for Indoor Limits and Outdoor Use
Last updated: 2026-09-29
What a propane heater is allowed to do
Short answer: The Mr. Heater MH9BX page calls that model indoor-safe and lists 4,000 or 9,000 BTU/h. The manual does not treat that flag as permission for every room. It is a portable propane heater for recreational and emergency indoor use, with a stated vent, stated clearances, and a disposable 1 lb cylinder. The MH30T page says outdoor use only. Mr. Heater says unvented heaters are prohibited indoors in Massachusetts and in Canada. That is the manufacturer’s statement. I did not open the statutes. On September 29, 2026 the manufacturer store showed $155.14 for the MH9BX and $182.66 for the MH30T. Those prices are the heaters, not propane.
I live in Washington State and I use a truck-bed camper. Cabin heat when the power is out is the other place this question shows up. This is not a roundup and not a recommendation to buy either model. These are the two Mr. Heater pages, and the MH9BX operating instructions, that were opened.
An indoor propane heater label is a starting point. It is not a blanket yes.
Two pages, two different jobs
The MH9BX product page describes an indoor-safe radiant propane heater that emits 4,000 or 9,000 BTU. The spec table lists input of 9,000 BTU, indoor-safe Yes, an oxygen depletion sensor Yes, and maximum elevation of 7,000 ft. Regular price shown for the heater, not a cylinder, was $155.14 on the manufacturer store on September 29, 2026. That is not a hardware-store shelf price.
The MH30T product page describes an outdoor radiant propane heater that emits 10,000 to 30,000 BTU. A bullet says outdoor use only. The spec table says indoor-safe No. A disclaimer says outdoor use only. Tank-capacity minimum is a 20 lb propane cylinder, with a direct connection to a 20 lb bulk propane tank. Regular price on that manufacturer page was $182.66 on September 29, 2026. That is the heater, not fuel. The page that was opened does not state clearances or a burn rate, so I am not adding either.
If you came looking for a propane heater outdoor setup, the MH30T page is the one that says outdoor use only. It is not interchangeable with a heater the maker marks indoor-safe. I am not ranking them. I am keeping the labels apart so I do not put an outdoor-only tank-top heater in a cabin.
Heat output and fuel use, without a fuel price
The MH9BX page prints burn rate as 0.044 gal/h at 4,000 BTU and 0.099 gal/h at 9,000 BTU. The spec table lists run time of 3 hours at maximum BTU and 6 hours at minimum BTU.
The MH9BX US operating instructions, page 5, say operating time will be approximately 3 to 6 hours on one 1 lb cylinder and 48 to 110 hours on a 20 lb cylinder, based on HI and LO settings. The manual spells “cylinder” as “cyclinder” in that sentence. I am using the manual’s “about 3 to 6 hours” and “48 to 110 hours,” and the product page’s 3 hours at max and 6 hours at min. I am not using a separate marketing line on that product page that does not match the spec table.
| Published figure | What the source prints |
|---|---|
| Input | 4,000 or 9,000 BTU/h on the page; spec table input 9,000 BTU; manual table 4,000/9,000 BTU/h |
| Burn rate | 0.044 gal/h at 4,000 BTU; 0.099 gal/h at 9,000 BTU |
| Hours at max and min | 3 hours at maximum BTU; 6 hours at minimum BTU |
| 1 lb cylinder | About 3 to 6 hours |
| 20 lb cylinder | About 48 to 110 hours, HI and LO |
| Heater price, 2026-09-29 | MH9BX $155.14; MH30T $182.66 |
There is no dollar-per-hour result. No propane retail price, cylinder price, or refill price was opened, so I will not invent one and multiply it by 0.044 or 0.099. I will not convert gallons to pounds. No pounds-per-gallon factor was opened. I will not multiply gal/h by the stated hours and call that the cylinder’s capacity. The hours are the manufacturer’s stated hours.
The EIA units page gives a sample factor of 91,452 Btu per gallon of propane. The page says factors are recalculated each year and current factors are updated annually in Appendix A of the Monthly Energy Review. That sample is not a retail price and not a pounds-per-gallon factor. I am not turning 91,452 into a cost for a weekend in the camper.
The manual says to use only 16.4 oz (1 lb) disposable cylinders that mate with a No. 600 valve connection. Emergency indoor heating, in the manual’s words, is when the heater is connected to a disposable 1 lb propane cylinder. The same instructions say never bring a refillable propane cylinder indoors. The 48 to 110 hour figure on a 20 lb cylinder is still what the manual prints. It does not cancel the ban on bringing that refillable cylinder inside. I am not describing a hose or an install the manual excerpt does not describe.
Where the manual says indoor use actually is
The cover of the MH9BX instructions says portable propane heater for recreational and emergency indoor use, and for US sale except Massachusetts. Page 2 says not for use in a dwelling home in California.
Page 5 says the heater is safe for indoor use in small recreational enclosures with combustion air and ventilation, such as enclosed porches, cabins, fishing huts, trailers, tent trailers, tents, truck caps, and vans. That list is specific. My truck-bed camper is not named. Truck caps and vans are. I read my rig against that list, and I still have to meet the vent, the clearances, and the rule against running it while sleeping. I am not treating the product page’s “indoor-safe Yes” as approval for every enclosed space I own.
The manual also says never operate the heater while sleeping. Bathroom use is LO only. Bedroom use is HI or LO. Those limits are in the same clearance table as the BTU input, on page 3.
Clearance, ventilation, and a different three-foot tip
Page 3 of the MH9BX manual lists clearance to combustibles as top 30 inches, front 24 inches, sides 6 inches, and rear 0 inches.
The same manual says the heater requires a minimum vent area of 9 square inches, with an example of a 3 inch by 3 inch opening, at the ceiling and at floor level. When the heater shuts off, troubleshooting says to replace the oxygen depletion sensor and to provide a minimum fresh air opening of 9 square inches. The product page says the MH9BX has an oxygen depletion sensor. The manual does not print an oxygen percentage for that shutoff, and it does not describe the sensor as a carbon monoxide alarm. I am not filling in a percent.
CPSC release 26-237, January 30, 2026, says keep all sides of a portable heater at least three feet from beds, clothes, curtains, papers, sofas, and other items that can catch fire. That three-foot line is a general portable-heater fire tip. The 30 / 24 / 6 / 0 inch figures are the MH9BX manual. They are different numbers. I do not average them into one clearance.
Above 7,000 feet, the manual says the heater may shut off. The product page lists maximum elevation of 7,000 ft. I do not camp that high in a typical Washington weekend, but the shutoff line is still the one printed, not a guess about my usual trailheads.
Carbon monoxide and sleep
The CPSC page on portable heaters and camping equipment says do not use portable heaters or lanterns while sleeping in enclosed areas such as tents, campers, and other vehicles. CPSC says this is especially important at high altitudes, and that people die every year from carbon monoxide poisoning from portable camping heaters, lanterns, or stoves inside tents, campers, and vehicles. Symptoms listed are headache, dizziness, weakness, nausea, vomiting, sleepiness, and confusion.
That matches the MH9BX manual’s ban on operating the heater while sleeping. In the truck cap or a cabin bunk, the heater is off before anyone sleeps. I am not treating a small enclosure as an exception because the product page says indoor-safe. The manual’s own list includes tents, trailers, and truck caps, and it still forbids sleep operation, and CPSC says the same for tents, campers, and vehicles.
Massachusetts, Canada, and California, as Mr. Heater states them
Mr. Heater’s Buddy Series University page says this class of heater is restricted from all indoor use in Massachusetts and Canada, and restricted from use in dwellings in California. The FAQ on that page says that according to Massachusetts law, unvented heaters are prohibited from use indoors, and that according to Canadian law, unvented heaters are prohibited from use indoors.
I am citing Mr. Heater’s statement. I am not citing a statute I opened, and I am not turning it into a national rule. The manual cover already says for US sale except Massachusetts, and page 2 already says not for use in a dwelling home in California. Those lines agree with what Mr. Heater’s own page says. They do not tell me Washington’s rule, and I am not inventing one.
No cabin building-permit requirement was on the CPSC or manufacturer pages that were opened. I am not adding a permit step the sources do not state.
Washington is not Massachusetts, and it is not Canada. That only means the manufacturer’s “except Massachusetts” sales line is not naming my state. It does not mean my cabin or the camper is automatically an approved room. The places the manual lists, the 9 square inches of vent at the ceiling and at the floor, the clearances, the disposable cylinder, and the sleep ban are the limits I can actually repeat.
The outdoor model stays outside
The MH30T, at $182.66 on September 29, 2026, is the propane heater outdoor case in the pages that were opened: 10,000 to 30,000 BTU, outdoor use only, indoor-safe No, minimum tank a 20 lb propane cylinder, direct connection to a 20 lb bulk tank. I do not have a clearance or a gal/h for it. Using the MH9BX’s 30 / 24 / 6 / 0 inches, or its 0.044 and 0.099 gal/h, on the MH30T would be borrowing numbers from a different model. I will not do that.
A tank-top heater the manufacturer marks outdoor-only is a porch or open-air tool. It is not a backup plan for the inside of the camper when the smaller heater’s cylinder runs out.
What I still cannot put in dollars
I can say the MH9BX heater was $155.14 and the MH30T heater was $182.66 on the manufacturer store on September 29, 2026. I cannot say what a 1 lb disposable cylinder costs, or what a 20 lb refill or exchange costs. Those prices were not on the pages used here. Without them, 0.044 gal/h and 0.099 gal/h stay fuel-use rates, not a trip budget.
The 3 to 6 hours on one 1 lb cylinder, and the 48 to 110 hours on a 20 lb cylinder, are the runtime claims I will repeat. They are the manufacturer’s stated range across HI and LO, not a calculation I did from the burn rate.
Electric heat is a different problem, and I do not have its wattage
A cabin that already has a battery box sometimes looks at an electric heater instead of a propane heater. I am not stating an electric heater’s wattage. No manufacturer or energy-department page for that wattage was opened for this draft, so I will not supply one.
If you want to ask how long a space heater runs on a 1,500 Wh power station, that question has its own page: how long a space heater will run on a 1,500 Wh power station. Linking it is not me stating a heater wattage, and it is not me stating the hours. The tool is there for a load you already know.
Cabin context on this site is cabin off-grid and the complete off-grid cabin power setup. The battery boxes themselves are under portable power stations. None of those pages replace the MH9BX manual’s vent, clearance, or cylinder rules.
How I read this in the camper and at a cabin
For a portable propane heater inside a recreational enclosure, the only model in these pages with an indoor-safe flag is the MH9BX, at 4,000 or 9,000 BTU/h, 0.044 or 0.099 gal/h, about 3 to 6 hours on a 1 lb cylinder, clearances of 30, 24, 6, and 0 inches, and a minimum vent of 9 square inches at the ceiling and at the floor. The cylinder indoors is the 16.4 oz disposable one with a No. 600 connection. A refillable cylinder stays outside. The heater is off before sleep. Bathroom use, if the manual’s location even applies, is LO only.
The MH30T stays outside, at 10,000 to 30,000 BTU, on a 20 lb tank, with no clearance and no burn rate copied from the other model.
Mr. Heater says unvented heaters are prohibited indoors in Massachusetts and Canada, and restricted from dwellings in California. I repeat that as Mr. Heater’s statement. I do not have a fuel price, a pounds-per-gallon factor, an oxygen-shutoff percent, or a cabin permit rule, so those stay out of the budget and out of the advice.