Blue Flame heater won't stay lit

kurtosMarch 26, 2012

Hi Everyone!

I just recently got a vent free 20k btu Mr Heater blue flame for my greenhouse. Problem is it won't stay lit. This originally happened the very first night I set it up. Figured it was a oxygen problem so ran a 4" pipe to underside of heater and taped up the rest of the intakes as suggested by another post on here. It worked good for one night and then back to not being reliable. It will sometimes only stay on for 10 minutes and other times it would go all night. I also used compressed air and cleaned it out per the manual (though I didn't think this would help as it was brand new). This didn't seem to make much of a difference. I also have my doubts as it being a dirty thermocouple issue as well being how it is new.

The pilot flame is just blue as it should be and does not show any orange or otherwise which would indicate it being dirty. I have a 100# tank with a 10ft hose attached. I don't think it is a draft either as the wind does not blow much here and when it does it doesn't seem to make a diff on performance anyway. My greenhouse is very air tight and insulated. Is it possible a 4" supply is not enough or maybe the oxygen is just not being pulled in enough (I am running less than 30" from heater to outside in a straight shot)? The outside of my pipe has a dryer vent attachment without the flappers installed. I have taken this completely off to just leave the pipe wide open but this also doesn't seem to make a diff.

Any new ideas would be appreciated. I've searched and searched on here and can't seem to find my solution. Thanks so much in advance.

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poppa(z5 MA)

beside calling the company, i'd check for something in the pilot line feed... a spider for example. You might blow it away from the opening but then pressure pushes it back?

How about low pressure to the pilot feed? is there a valve or pressure reducer/regulator somewhere?

I'd call the company.

    Bookmark   March 29, 2012 at 9:29AM
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I'd guess that the built-in low oxygen sensor is shutting it off. An intake duct isn't going to allow much fresh air intake if the rest of the greenhouse is sealed up 'tight as a drum' and the heater is consuming oxygen from 'trapped' air.

You might try deliberately cracking a vent in an area away from your heater location to allow for some convection 'draft' ... which should allow oxygen depleted greenhouse air to exit, and draw in 'new' air to replace it via your intake pipe.

    Bookmark   April 13, 2012 at 2:21PM
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sandy0225(z5 Indiana)

Yep, I bet your greenhouse is too tight. I have a blue flame type on my glass greenhouse lean to against the house and we have to keep the basement window open with a fan blowing fresh air into the greenhouse to keep the heater lit. If the fan goes out so does the heater.

    Bookmark   April 30, 2012 at 8:51PM
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etravian(Zone 6 CT)


I apologize for the extreme lateness of my reply. Seems my junk mail filter is a touch overzealous, but it's great that you're getting other feedback on this too.

So there were two things that really made the biggest difference on keeping the blue flame heater alive at night in the sealed gh. One was the incoming pipe from the outside, and the other was the sealing off of the rest of the air inlets on the heater.

As I dig through my photo archive here… I guess I can start at the beginning…

8x16, mostly double layer plastic hoop house. Note the thing jutting out to the right of the door, attached to the inside wood brace. That's the dryer vent cover. Up close:

Inside there is the flap for one-way airflow. This is really important because you just don't want warm air being blown out through the sidewall. The lower you can mount the vent, the better, to take advantage of natural convection currents.

On the inside:

The fan is there to shove the heat down the length of the gh. Note how the piece of air register vent metal is attached [and reasonably well sealed] to the heater. I also pulled the thermostat bulb out from the heater housing so it would be more exposed to the greenhouse air… which helped better regulate temps.

Skipping ahead a couple revisions here:

Better sealed.

And time-warping again to a subsequent revision:

Note how black duct tape takes on a decorative and functional role around the front… completely obscuring the holes.

The top vents stay open, as those actually have nothing to do with combustion air. That's where the heater's internal fan hangs out and does a pitiful job of blowing air around. I don't bother with it.

My original version of my greenhouse was REALLY heat lossy, as I had to cut too many corners for fiscal reasons. Ended up paying for that with the loss of most of what I started that first year:

It was nice for awhile at least… :)

The plastic was contractor grade… not UV treated. About a year later, it finally gave up the ghost… life got in the way… and I had to effectively abandon ship.

But the durable parts got a second life

Slightly smaller, but built smarter.

Note the insulated north and west walls. Still double layer plastic… still contractor grade, but much easier to replace given the size.

And there were much happier plants. Also got some work done in there - hooray for wifi!

Sadly, after about a year I moved out from this location, and the gh was dismantled yet again. The heater and a few other items will be making the jump to a new greenhouse I am designing for this year. This one's going to actually have a PLAN first, and will be using a whole bunch of windows that we replaced in our house last year.

The heater will live on… It's in the basement, just waiting for me to fire it back up again! :)

Hope this helps a little. I've recently made some new friends in the area and will be helping them to put together their first hoop house. Between my plans - where I know for sure I am over engineering things simply because I don't know any better - and the plans my new friends have... I hope to be up to my eyeballs in experience by the end of the year!

Best of luck - and drop me a line if you have any questions. I promise to not let your email end up in my spam bucket. Oh, one thing - I don't have a clue how GardenWeb lets you reply to an email that you send thru GardenWeb... there doesn't seem to be a 'GardenWeb Inbox' or anything like that... so while I got your email [eventually] I could only respond by doing a post. *shrug*

    Bookmark   April 1, 2013 at 12:42PM
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Thanks to all for the suggestions, especially etravian as he gave me the original idea of fresh air via a dryer vent.


Initially I ran a dryer vent setup similar to etravian's. I taped off the extra heater holes but did not tape the dryer ducting to the heater as suggested. My problem continued to occur in that it was continually shutting off due to lack of oxygen. I think the heater was still able to get the oxygen from inside the greenhouse rather than through the ducting as this was the path of least resistance.

This year I added an inline duct fan which helped pull air from outside to the bottom of the heater. This has 100% solved my problem. The downside to this is I have burned double my propane usage (usually 100 lb's to 200 lb's) for the season.

My thoughts to rectify this are to either better seal up the air duct to the heater so there would be zero oxygen draw from inside the greenhouse or put a variable speed light switch for the fan and reduce the speed so not as much cold air will be drawn in. Maybe a timer set to intermittently run the fan would achieve a better result as well. I'm hoping the duct sealing will work as it seems to for etravian.

I can post pics of my setup if anyone cares.

    Bookmark   April 14, 2013 at 7:20PM
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