I'll add my two cents (two BTUs?): My first greenhouse (1988) was a lean-to on the side of an unheated garage. I had a 30000 BTU Modine unit heater, propane fuel, externally vented that was overkill but worked well. It had a standing pilot which meant I lit the flame in the fall and turned everything off for the summer. My current greenhouse (2000) had similar Modine unit heater but with an electric igniter as opposed to a standing pilot. After about 12 years it failed to ignite on a cold night, and the greenhouse dropped to 28 degrees, with remarkably little damage to plants. The repair guy said the igniter should be replaced which I did myself. He also said that greenhouses should use unit heaters with sealed combustion chambers. This means that it draws in air from the outside instead of using the humid air from inside. After replacing the igniter it was fine for a while, but it became apparent that it failed regularly if the thermostat was set to below 45 degrees F. Above that temp, it was reliable, but for how long? I toyed with replacing the high voltage transformer for the igniter, but decided to cut my losses and get a new furnace. I wound up with a Reznor sealed combustion furnace, again 30000 BTU, the smallest they make. It's been fine. But it is still overpowered for what I need. My greenhouse is a semi-pit type, 11' x 21', that is sunk into the ground by ~28", and is a lean-to against an unheated garage. Glazing is two wall 10mm polycarbonate. It is actually better insulated that I expected, and does not take many BTUs to heat it. I found that a single 5000 BTU space heater (the kind that runs off of a 15 amp 120V circuit) will easily keep the inside tamperature at least 25 degrees above the outside. Adding a second space heater that only runs if the first can't keep up lets the system function to below 0 degrees F. Cost-wise, it's a wash. Propane is quite expensive here if you don't use it to heat the entire the house, and electric is comparable in price (there's a formula that converts propane $/gallon to electricity $/watt-hour). I still have the propane and run it from time to time. It's also insurance in case we lose power. I have a generator, but it's not big enough to run the space heaters and other stuff in the house. If I did everything again I would have used forced hot water heating that is hooked up to the main furnace in the house. Hindsight is wonderful. Back to Steve's question, you should at least keep a spare igniter on hand. The points get corroded, but that might not be the whole story as I found. --Roy NW of Boston On 11/1/2021 12:52 AM, Steve Marak via pbs wrote: > While on this thread, may I ask those who have or have had > purpose-built greenhouse heaters, especially Modine, what have been > the failure points, please? Or advice about specific preventive > maintenance? > > This is our second year with a Modine externally vented heater in the > greenhouse, and I love it (and sleep much better when it's cold). But > Nick is right - there is some corollary to Murphy's Law that causes > heaters to fail when it's really cold and/or hard to get parts, and > even new heaters can have problems. I kept a fair inventory of > likely-to-fail parts for our previous heater that I could replace > myself in an emergency and would like to do the same for the Modine. > > Thanks, > > Steve > > On 10/31/2021 6:01 PM, Mark Mazer via pbs wrote: >> " After two decades in nice humid greenhouse the igniter is rusted to >> point where it cannot work" >> >> FWIW: After 20 some years, even the "Cadillac" of brands, Modine purpose >> built greenhouse propane heaters, are getting "long in the tooth"and may >> become unreliable. You may want to consider replacing it IMHO. Been >> there, >> done that. >> >> Best, >> m >> >> On Sun, Oct 31, 2021 at 12:55 PM Nicholas Plummer via pbs < >> pbs@lists.pacificbulbsociety.net> wrote: >> >>> Get a greenhouse, they said. It’s a relaxing hobby, they said. >>> >>> I keep my pilot flame burning all summer on my direct vent propane >>> heater—I figure its a small amount of propane in the grand scheme of >>> things, but I hope the heat will help to keep things dry around the >>> valve >>> and thermocouple. Which means that something else will probably >>> fail on >>> the coldest night of the year… >>> ... > _______________________________________________ pbs mailing list pbs@lists.pacificbulbsociety.net http://lists.pacificbulbsociety.net/cgi-bin/… Unsubscribe: <mailto:pbs-unsubscribe@lists.pacificbulbsociety.net>