View Full Version : CO any one

Cliff Rohrabacher
10-07-2008, 12:01 PM
Saw a cute little propane powered shop / garage heater in an Ace Hardware today.
It's just a scaled down air blast heater like you'd find on a construction site running on gas or diesel.

There were pictures of intended uses on the box one of a shop the other a garage. I coudln't help but wonder how long it'd take for the CO to build up to dangerous levels.

Tom Veatch
10-07-2008, 12:34 PM
Don't know anything about the one mentioned, but it is possible that CO wouldn't be a factor. Although I do think it would be a poor choice for a woodshop.

I once had a non-vented (by design) propane heater in my shop. According to the owners manual for the heater, it had oxygen sensors to shut it down if the O2 levels fell too low. I don't recall mention of any CO sensors, although that might have also been covered.

When I enlarged the shop, I replaced it with a vented heater primarily because it drove the humidity so high, water was condensing on the windows and running down the walls.

Matt Meiser
10-07-2008, 12:50 PM
Those forced air heaters are also noisy as @#$%. Jet engine noisy! They do work well though because of the air circulation.

I've had the same experience as Tom on the moisture issue. We also have an unvented propane fireplace in our house. When we use it for very long we get some condensation on the windows. The house is so dry in the winter it doesn't hurt to occasionally add some humidity but I wouldn't want it condensing on my cold tools.

Don Abele
10-07-2008, 1:16 PM
Cliff, this is a topic that comes up here a lot - the use of propane or kerosene heaters in the shop. One of my prior occupations in the Navy was as a Gas Free Engineer (testing/certifying atmospheric conditions on submarines). Here's what I routinely post here when people ask about this:

"Indoor rating or not, you have to make sure your shop is well ventilated. Propane, when burning correctly, produces carbon dioxide as a byproduct. When it isn't burning correctly, it produces carbon monoxide. Both are deadly in high concentrations - carbon monoxide at much lower levels.

Kerosene, on the other hand, always produces carbon monoxide and can also produce acidic vapors (read, not good for metal). It amazes me that these are still rated for indoor use.

The other thing to remember is that both produce MASSIVE amounts of water vapor. A pound of propane burned puts about pound of water vapor in the air and a gallon of kerosene releases roughly a gallon of water vapor.

Just as a comparison...natural gas produces about the same amount of carbon dioxide but only one quarter the water vapor as propane."

One thing to add is about the low oxygen level sensor. A lot of these units are now equipped with a sensor which will shut the unit off if oxygen levels fall below 16%. The premise behind this is that in a totally confined space, the unit will decrease oxygen to dangerous levels well before carbon monoxide or carbon dioxide reach critical levels.

Be well,


Cliff Rohrabacher
10-08-2008, 8:31 AM
Well if there's one place where there is a zero tolerance for dangerous accumulations of any thing it'd be in a US Navy Sub.

The other thing to remember is that both produce MASSIVE amounts of water vapor. A pound of propane burned puts about pound of water

Now, that's got my curiosity up. I gotta go look up the molecular structure of LP.

vapor in the air and a gallon of kerosene releases roughly a gallon of water vapor.

Just as a comparison...natural gas produces about the same amount of carbon dioxide but only one quarter the water vapor as propane."

That too. I've always taken these two for granted, never contemplating what the constituent compounds are, or what they produce when burnt -- besides heat.

Don Abele
10-08-2008, 9:38 AM
All right Cliff, you made me grab my notes (they're on my computer so it was pretty easy). It took longer to type out the equations than it did to look them up.

Warning - Chem 101 lesson coming...:p

(Subscripts are listed as (x) ) - couldn't figure out how to do this any other way.

C(3)H(8) + 5 O(2) --> 3 CO(2) + 4 H(2)O + Heat

If burned incorrectly you get:
C(3)H(8) + 4 O(2) --> CO(2) + 2 CO + C + 4 H(2)O + Heat
(notice this is where you get the carbon monoxide)

NG (Methane)
CH4 + 2 O(2) --> CO(2) + 2 H(2)O + Heat

If burned incorrectly you get:
CH4 + 3 O(2) --> CO(2) + 2 CO + 2 H(2)O + Heat
(again, the CO...but this is much harder to make happen than propane)

This is from memory (no notes on it) - This stuff is a mix of 4 different hydrocarbons. From gallon to gallon the amount of each can be different. You need to work up equations for each of the hydrocarbons as you can not write an equation for a compound. I don't have the specifics in my notes as this isn't something we would use.

One thing to note from above is that when they burn incorrectly it is the lack of oxygen that produces the carbon monoxide. As oxygen levels drop, the rate of carbon monoxide production increases. With propane it's a little more obvious as you start produces soot (carbon), you don't get that with natural gas.

By the way, some of my numbers were a little off (they were off the top of my head) - 1 pound of propane gives you 1.6 pounds of water vapor and 1 cubic meter of natural gas gives .66 pounds of vapor. These are not equivalent as you use less natural gas to produce the same btu as propane, which is why NG gives you about 1/4 the vapor as propane (btu to btu).

Be well,


David DeCristoforo
10-08-2008, 9:51 AM
In addition to the other issues mentioned here, these heaters can pose an extreme fire hazard in a wood shop. Fine dust can flash if it comes in contact with the flame or the baffles which can get "red hot". And any flammable material accidently left in close proximity to the "business end" of one of these heaters can get hot enough to combust. Watch out....

Al Willits
10-08-2008, 12:26 PM
I deal with Nat gas and propane, so this is all geared to wards them.

Couple things to remember.
A clean burning flame will/can produce little or no measurable amounts of CO, meaning amounts relating to heating.
If you run one of these heaters in a enclosed area, as the heater uses up the oxygen it will start producing CO, that's where non vented heaters come up dangerous.

If ventilated and there's enough airflow, no problem, also having venting in the ceiling helps as CO is slightly lighter than air and CO produced may work its way out of the building.

I have a friend who runs a torpedo style propane heater in his garage and after several hours his CO level at eye level is under 4ppm, safe at that level.
But he has vents in the ceiling and enough air exchange to work.

Here in Minn it is against code to install a non vented appliance in a bedroom, there's a reason for that.
People die from them.

So, I'd first recommend not using any of the non vented heaters, and if your bound to, add a CO detector to your shop, may save your life.
And my life isn't something I'd put in the hands of a cheap heaters sensor.

Nat gas moisture is either a bit acidic or caustic, can't remember now, but will cause rust or corrosion.

Either way, be careful, our company is who the fire dept calls for CO calls here, and when I was in the field I got to go on more than I cared to, some had body bags or needed them, and some we got to in time, almost all said they never realized they were being effected by CO and many thought they were just tired...wicked stuff CO is..damn wicked