Unvented gas space heaters aren’t legal in Minnesota, but that doesn’t keep people from installing them. Today, I’ll explain what they are, why I don’t like them, and why retailers sell them even though they’re not legal.
What is an unvented gas space heater?
Almost all gas appliances require venting to the outdoors. Furnaces, boilers, fireplaces, water heaters, clothes dryers, and the list goes on. One notable exception is a gas oven, which I’ll come back to. Another significant exception is an unvented gas space heater, also known as a vent-free heater, or ventless heater.
These are basic devices: they burn gas, which produces heat. Because there’s no vent, these are 100% efficient. That’s right, you heard me. All available heat stays in the room, so nothing is wasted. They’re very good at what they do, and all you need is a gas line. In fact, you could simply hook up a 20 lb propane tank, place it on the ground with feet, and have it out of the box and running within minutes. No electricity needed. And with the larger 30,000 BTU units priced around $200, it’s easy to understand how this is such an attractive heating option.
How is this different from an oven?
Gas ovens aren’t too different from unvented space heaters. Ovens don’t vent to the exterior, so 100% of the fuel used will heat the space it’s in. And the same goes for stovetop burners. The main difference is that gas ovens aren’t relied upon for space heating; you bake your food, then you turn the oven off. You don’t have it running all the time.
And not only that, but gas ovens aren’t all that healthy to begin with. It’s not good to breathe the byproducts of gas combustion, period. Yes, gas ovens have been allowed in the code forever, but building codes require an openable window or an exhaust fan in the kitchen. That’s the minimum code. I firmly believe every range should have a fan that vents to the exterior; especially gas ranges. And that fan should be operated whenever the oven or range is used. Check out my blog post on this topic for more info: Kitchen hoods are for all ovens, not just gas.
Why are unvented space heaters illegal in Minnesota?
Because they’re not vented, you end up breathing all of the byproducts of gas combustion. This is bad for your health and, in extreme situations, could even lead to death. To be fair, all of these unvented heaters are equipped with an oxygen depletion sensor. This will cause the unit to shut down if there’s insufficient oxygen for safe combustion. When it comes to life safety, these are probably safer to operate inside your home than gas ovens. But not when it comes to overall health, because they run for much longer than ovens.
Beyond potential health issues, unvented heaters produce copious amounts of moisture. A 30,000 BTU unit will put out 1/3 of a gallon of water per hour. And where does all of that moisture go? It condenses on the windows and walls and finds its way into the attic through attic bypasses. This can be highly damaging to Minnesota homes when it’s cold outside, and this is the main reason I don’t recommend using unvented space heaters, even in garages.
Section 621 of the Minnesota Fuel Gas Code says “Unvented room heaters and unvented decorative appliances shall not be installed in any dwelling or occupancy.” So does this mean they can be installed in a garage? That’s a grey area that’s left up to the building official. They’ll probably say no for an attached garage, and yes for a detached garage.
If they’re illegal, why are they sold here?
There’s a chance that someone wants to use a ventless space heater in a detached garage. If that’s the case, it’s not illegal, so retailers like Menards still sell them. They have warning labels on the shelf saying they’re not permitted in living spaces.
And there’s fine print on the box advising you to check state and local codes for permitted use. Is that enough? Clearly not, because we see them all the time.
On the other hand, they’re not sold everywhere. Home Depot refuses to sell these in their Minnesota stores, and they won’t deliver them to Minnesota residents. Good on you, Home Depot.
Summary
Vent-free space heaters produce a lot of moisture that can be very damaging to Minnesota homes (and garages). Besides that, it’s not good for your health to breathe the byproducts of gas combustion, and you’ll be breathing a lot of it if you use one of these. For these reasons, they’re not allowed in any Minnesota dwelling or occupancy. When we find unvented gas space heaters during our home inspections, we recommend having them removed.
