Kurt, 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… https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/P1010008.JPG 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: https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/P1010007.JPG 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: https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/P1010006.JPG 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: https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/PICT0031.jpeg Better sealed. And time-warping again to a subsequent revision: https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/PICT0029.jpeg 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: https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/P1010012.JPG 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. https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/100_0106.jpeg But the durable parts got a second life… https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/PICT0002.jpeg Slightly smaller, but built smarter. https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/PICT0019.jpeg Note the insulated north and west walls. Still double layer plastic… still contractor grade, but much easier to replace given the size. https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/PICT0024.jpeg And there were much happier plants. Also got some work done in there - hooray for wifi! https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/PICT0022.JPG 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! :) https://dl.dropbox.com/u/374870/GardenWeb%20Post%20Pics/PICT0021.jpeg 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*

I used a 30,000 blue flame last year as a backup to a 4000 watt hot shot in a 10'x40' dbl. poly and it worked fine. I also have a 18" box fan on a bench above both heaters to force the air to the other end of the houses (where I have another blowing back to the front) and I find fewer cold air pockets around the house. The 4000 watter seems to be able to keep the houses at around 50 degrees until the outside temp gets down to 20 or so then it can't keep up and the blue flame kicks on for a few minutes. It kicks in a couple of times an hour so the 100lb propane tank lasts 3 to 4 weeks, depending on the weather of course. Happy planting Steve

In principle, it is possible to replace the gas log unit with a new one of which there are many on the market. But you would need to figure out if it will work properly, and that depends on the specs of the fireplace and the specs of the new gas logs you want to install. That may not be easy to determine, and it could be dangerous to install a gas log unit that is not compatible with the fireplace. You mentioned that the blue color of the gas flame looks fake. There is probably a way to fix that, by adjusting the pressure on the gas jet. Maybe it just needs a service call to clean it out.

I have this and like it. Yours is nicely filled out for being new.