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Blue Flame heater won't stay lit

12 years ago

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.

Comments (11)

  • 12 years ago
    last modified: 9 years ago

    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.

  • 12 years ago
    last modified: 9 years ago

    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.

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  • 12 years ago
    last modified: 9 years ago

    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.

  • 11 years ago
    last modified: 9 years ago


    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*

  • 11 years ago
    last modified: 9 years ago

    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.

  • 8 years ago

    Great pictures and ideas everyone. I had my first greenhouse in 1997 and then mothballed it in 2004 to raise a family. It was heated by a vent free blue flame heater-which was new back then. I had very few issues with the heater turning itself off...and after reading here and other places, I think that was because I had it connected to my bedroom window which supplied it with a fresh amount of oxygen. My new version is slightly bigger and not connected to my bedroom and now I am having issues with the heater turning off. Etravian I think your idea of creating an air intake tube with a dryer vent is ingenious. It makes it work along the lines of a pellet stove intake pipe(I am considering a pellet stove for heat also.) I am getting ready to attach the dryer venting soon. I am nervous but those of you who have tried the "intake dryer tube" idea, is it is still working for you? To see Molly D's report of it heating the house to 63F when it is 0F out is encouraging. My other question is, where does all the heated air go-meaning can you keep forcing air into the greenhouse like that without issues? Am I not getting something here? Does there need to a vent at the bottom of the greenhouse to move the cold air out-since you are not using it for combustion at the heater? Am I overthinking this? It is so unnerving to come into the ghouse and see the pilot off this last week. Right now we are just dipping below freezing at night(Kansas City) but in a few weeks it will be way colder and I will not have the luxury of the heat trapping nature of my inflated polyethelene plastic walls nor the IR plastic that keeps in infrared heat. Thanks to anyone who replies. It is amazing how little there is on the internet regarding this issue. Esp since non vented heaters have been out now for 20 years.

  • 8 years ago

    Update to my previous post. I completely solved my problem by removing the inline duct fan and more importantly sealing my vent to my heater so the only draw it gets is directly from outside. There is no draw from inside the greenhouse at all. I use maybe $100 in propane (mid March - first part of may, lows typically 20 degrees). I don't think having another vent to exchange air is needed. The draw for the heater is needed for flame. air output is neglible I believe. Plus your greenhouse is not 100% sealed so any 'excess' air would find its way out. Having another outlet would translate into a lot of money wasted in heating. this has worked flawless for me the past 2 years. I've had zero pilot outs. Hope this helps as I too was driven crazy trying to solve this issue.

  • 8 years ago

    Kurtos, thank you so much for taking the time to update your post. Yes, your original post was throwing me off with the in-line fan. ...I was thinking ought oh, maybe it doesn't work so great after all. It sounds like sealing the duct work to the back of the heater is the key. Thank you so much. That is what I am working on now-trying to find some duct work that is 16 inches long to completely cover the slot in the back. (ProCom 30K BTU vent free.) I am thinking I am going to cut a couple of pieces and tape the duct work together. I read on Dave's Garden forum that you need roughly a square inch of intake per 1000 btu. In my case that would be 30 inches or an 6-8 inch diameter intake hose. I think they have those at Home Depot. I had been contemplating moving to a pellet stove because of this but that costs 5x what a vent free heater does at the outset plus it marries me to the greenhouse with pellet reloads a little more than I would like at this time -even with the large hopper. The air intake principal is the same for a pellet stove as it also has an intake for fresh air so this all makes sense. There is also information about venting the Southern Burner greenhouse vent free heater. They say to put an exhaust vent at the top of your greenhouse withi 12 inches of the top to draw air in from a small diameter intake pipe behind the heater on the floor. That just seems like a huge energy waste. I will get back to you and let you know. Right now the greenhouse is pretty tight and the heater is going out each night. Thanks.

  • 8 years ago

  • 8 years ago

    Wow that is an amazing garden you have. Just beautiful. (!!!) Thank you so much for getting back to me with those pictures. I noticed you do not have front vents on the heater at the bottom taped off like Etravian and MollyD? Also I noticed that your intake goes *under* your heater. I will have to look at my heater to see if there is a vent under there. Great idea on the cinder blocks. Yes I have left the greenhouse side open at the bottom of the greenhouse(I have a the 6 mil poly film) and have noticed on windy days the pilot stays lit, which goes against my earlier theory in years past that my pilot was being blown-out by the wind... I am getting ready to do a lot of maintenance work on it this weekend because we are having El Nino warm weather this month. I have been experimenting the last few days. It seems that if I leave the heater on a setting that is less than 1 on the dial, the pilot has more of a chance of going out. I am not sure why this is yet. I have gone to Home Depot and priced out the foam board with the shiny side insulation for the N wall, it isn't too expensive. I will be doing that, as well as some hay bales around the sides. 70F, wow that would be perfect. Right now I have the inflation operating at the top(because we had 5 days of rain and rain will bend the steel if it pools on the plastic-and this is heavy duty steel too) and got the air transfer kits for the sides, that should really steady the temperatures. I have not bought Solexx or any kind of material like that. I don't know what the R value would be compared to the insulated double inflated poly.