Here are a couple of sites that may help you . . . http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200306161_200306161 http://www.acehardwareoutlet.com/(p3vtyg55ms45sb55jiwf3heu)/ProductDetails.aspx?SKU=41015 Joe

We have been talking vent free heaters for years now. I was the one that started it 6 or 7 years ago. Just goto Lowes or Depot or your building supply store or some place that has a heater. Get one! Hook it up, check it and make sure you have the right connections, and your ready to go. You can get propane or natural gas and you can get many different sizes based on your size greenhouse and min low night temps. It todays world, gas is about the only way to heat a greenhouse and feel safe that your plants are ok. Trigger is telling you the truth.

Thanks so much for the info. I think I will go ahead and put the heaters on the exterior walls. Can't seen any advantage to putting them indoors and the disadvantages seem to include using up interior space, the added expense of special venting, and my worry about having propane indoors anyway! davidandkasie, I didn't realize I had used the word "tank" when asking about where to mount the TANKLESS water heater. Duh. Have had regular water heaters all my life and I guess I just tend to talk about water heaters as "tanks". I do know that propane tanks have to go outdoors... as if anyone would have a spot in their house for those monsters anyway (LOL.) Sorry about the confusion. I'm also not real keen about having a water storage tank (for preheating purposes) in the attic but, around here, builders put water heaters in the attic all the time anyway. (Slab foundations are de rigeur so nobody has a basement where they can go.) Since our attics get so darn hot most of the year, I guess having the water heater in the attic probably saves on heating bills but you're right about the danger of having a leak. Plus, getting a regular water heater OUT of the attic is such a chore that most people don't bother to take the old ones down when they get a replacement. Eventually their attic winds up being a "water heater graveyard!" We will have "walk in" access to our attic space though so getting to/from shouldn't be a problem. To avoid water leak problems, I'm thinking I will get a big black poly (rubbermaid) "stock tank" to set the preheating storage tank down inside of. Will also add an alarm to warn me if there is a leak. Hopefully that will do the trick. (Oh, and I guess I'd better make sure my insurance covers water damage from leaking pipes and water heaters.)

going on the info i have I would say that you have a bad thermocouple. It is part #18 on the parts break down. that is the part that you are warming up when you hold the fuel button down for 15 seconds. it has to send a signal to the gas valve that there is a flame present for the gas valve to stay open after you let go of the fuel button.