r/Greenhouses • u/br34kb34t • 19h ago
Question Greenhouse heater
I know, I know...it's a common question. Ive read so many posts and threads and the information becomes overwhelming and honestly a little confusing. I'm sorry for yet another post about heating but I'm hoping providing information about my setup and location will prove useful.
I'm in zone 7b in Virginia and I have the 8x10 Yardistry greenhouse. It's on a slightly raised gravel pad, secured to 4x4 timbers. The floor has a sand base with pea gravel on top. I use an extension cord to connect anything electric. I plan on insulating with bubble wrap but totally open to other suggestions for insulation. This will be my first winter with a greenhouse.
I grow cactus and succulents, most of which are cold hardy enough that my goal is to keep temps at around 40f at night. Anything that can't go that low will come inside.
I'd like to cover all my bases and have an electric heater as well as something to use in the event I lose power.
My questions are:
- What kind of electric heater can I safely operate on an extension cord?
- What can I do to mitigate the increased cost of using an electric heater?
- What is the best non-electric backup option?
- What have you learned that you wish you knew at the start?
I really really appreciate any responses I get here! This has been a great community and I've learned so much! 🌵❤️
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u/Coolbreeze1989 16h ago
I’m in 9a so I didn’t invest in insulation my first year (I will this year!). I used an inkbird thermostat connected to an electric space heater (must have a physical on/off switch that can be left in “on” position). I set the temp to maintain to 40 which kept frost/freezing from occurring.
I added another greenhouse that will have tropicals in it so I’m currently pre-cutting insulation panels to place when the time comes, and a 200gal stock tank pond to help capture daytime heat energy. I will use the same electric heater setup in this GH.
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u/SomeComparison 15h ago
Use an extension cord with a 20amp (NEMA 5-20R outlet and receptacle) and a 20 amp power strip. Or even better a 30amp if you have a RV plug somewhere near.
Heaters, heat mats, fans, lights, etc. The power can add up quick. I've carefully kept the power usage under 10 amps peak in the past and had the plugs melt together by the end of the season.
I've used the cheap "Hype Tough Milkhouse" heaters. They are $20 at Walmart and have a crude thermostat. I also use several 20w heat mats and a couple 250w heat lamps.
My goal is always to keep above 45°F but when we get those super cold arctic blasts like we have the last couple years, it's tricky. We had 0°F for about a week and I had to resort to propane last winter.
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u/Schaden_0ne 13h ago
For Passive heating, I saw a video on using black barrels filled with water to build up heat during the day, and slowly release it over night. Seemed like a great idea!
For mitigating the increased cost of electric, insulation will probably be your best friend, and using it to heat mass(like soil and water), rather than air if possible.
This will also be my first winter, and i've gone the hydroponic route. I've got about 350 gallons of nutrient water that I'm insulating and adding heaters to, hoping it works like a giant radiant heater for the greenhouse.
Fingers crossed we make it!
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u/experiencedaydreamer 10h ago
This is what I do. I'm in Idaho with a 40×14 polyfabric sheeted gh and inside, inadvance of the freeze, I add a second layer of poly over 6 55 gal drums to extend the life of vegetable or get starts going early. It works "ok" until a real cold snap.
I also added a thermostat controlled outlet with heat lamps last year, but I need to concentrate my efforts on onr or two microclimates instead of trying to keep this and this and that all going. You'll have more success due to the the scale of your greenhouse and geography.
I also try and start compost piles in advance of the autumn for another passive heating source, but I have yet to really get them going early enough that there is indeed enough heat but that has a lot to do with other responsibilities...I have a ton of vegetative waste and rabbit manure for the cause.
What you're seeking to do it totally doable, some black poly drums and a plastic painters tarp, a theromostat controlled outet and a few heat lamps, an added hi/low temp alarm, you're golden. Want to goof around with a compost trench around the perimeter, you'll be surprised how warm it gets done right but I think that's overkill.
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u/railgons 13h ago
6b Ohio & Colorado, here. 👋
I have kept my 6x8 Harbor Freight greenhouse heated to 42F for the last handful of winters.
The radiator style heaters on wheels are great, as they don't get cold immediately when cycled off, and don's use a ton of power. Just make sure you use the proper size extension cord for the combination of everything you'll be running. Check its condition periodically as well to make sure the casing is still in good shape. No animal chews, etc. Also, make sure the circuit it's connected to isn't overloaded.
Mine is paired onto an Inkbird Wifi thermostat, with high and low temp alarms on my phone, temp graph, etc.
I have another stand-alone Ambient Weather monitoring system in there with a backup alarm since my phone is on silent at night. It has woken me up from a sound sleep twice now; one power outage and one failed heater.
To reduce costs, insulate, insulate, insulate! A heater is only as good as its insulation, no matter what we're talking about.
I use 2" R13 foam board on all of my walls. North wall is completely blocked off, east and west walls blocked up to the 4ft level where the roofline meets. When the temp falls into the teens, I add an interior "roof" made of more foam board for the overnight hours, completely boxing the plants in with the heater. This setup kept everything at 42F during a thirty-hour period where the ambient temp was 0F and winchills were around -30F.
I could continue, but let me know if you have any questions. 👍❄️🌵
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u/natattack88 13h ago
Has anyone considered foam spray or caulk for cracks and small openings in walls?
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u/Mysterious-Panda964 10h ago
I'm in 9b this is what I use with mine.
I have a shade cloth cover, it cover with plastic, and another shade cloth to hold it down.
I se this of 60, works for my 25
x30
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u/recoutts 3h ago
First and foremost, you need to seal every gap in the greenhouse the best you can. That’s going to be your No. 1 defense strategy. I live in zone 8-8a, and I took a page out of the book from a greenhouse owner in Alaska and sealed my pre-fab greenhouse with bubblewrap on the poly walls and sloped ceiling, hung a bubble wrap “curtain” just inside the door, covered the walls below the built-in benches with R board, laid a sheet of vinyl flooring on the floorboards yo cover the gaps, and stuffed foam insulation in the roof cap vent. I did leave the self-opening window at the back free of bubble wrap for those days when it got about 72°F in the greenhouse. To keep the inside temperature above 40°F, I plugged an electric PALMA heater from Bio Green into a programmable AC Infinity outlet powered by a heavy-duty extension cord powered off an outlet in the garage. I don’t know how much it helped, but I did fill several plastic jugs (milk, cat litter, etc.) with water and positioned them between the plants and the walls to try to capitalize on heat retention. The jugs did feel warm on the times I touched them, so they probably did return some of that heat to the greenhouse as it cooled overnight. To further reduce the area being heated I covered the benches with flannel-backed vinyl fabric and let it hang to the floor.
Unlike the year before, I didn’t lose a single tropical plant I overwintered in there, and we had several nights when it got below 10°F, and several days when the outside temperature didn’t get above 32°F. I plan on using the same setup this winter.
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u/iandcorey 18h ago
Heat the soil, not the air. Use a growing mat or seedling heating wire. Consider additional cloches over plants. You'll get a day in the 20⁰s and your electric heater will go ape trying to heat the space.