Getting ready to buy one....

OK, other than the confusion of WHICH greenhouse to get (size limitations) I seem to have found all the answers I need here, but, how much success can I expect with a greenhouse in winter? I want to use it for overwintering tropicals and tender perennials, VA does get quite cold for a short period during the winter, can I expect a huge electric bill? We did have a "blizzard" last winter with a few inches of snow (I am from the north og Norway originally, 15" of snow is very little to me) and a few times with frost (again, not to me, but apparently it was cold). I only have room for a small greenhouse, (8 x 6). Any input would be great, I have the small space, I have permission from HOA and the greenhouse will be in a fairly sheltered spot. Now I just have to decide if it will be worth ordering it and setting it up before fall/ winter sets in or wait until next year.

Bec, we can figure this out, but first a few questions...

Will you heat electric?
What is your zone?
What is the greenhouse glazing? 4mm twinwall? 6mm twinwall?
What minimum temp will you want to keep? I have tropicals in my greenhouse, and I keep 54F in the winter. Plants need one temp to just survive, but a higher temp to grow.

A couple of notes...

8x6 is a smaller greenhouse. Smaller greenhouses heat up fast and cool off fast. You probably won't have much room for thermal mass, given size constraints.

SB

All good points, SB.

And if heating with electric I'd recommend a back-up source of heat for when you have power outtages (if any). Better safe than sorry.

Shoe

Hmmm, well, I thought I had it all figured out...LOL
Zone is 7a/b, very protected area in my back yard.
Yes, I will be heating electric - have no other choice?
Don't know the glazing yet, guess it all depends on what I buy eh?
I was assuming 54 to 60 for the tropicals, now, I might add some C&S as well, I am thinking staying with the same temps will be ok for them as well.
Primarily what will be in there is tender perennials in pots, C&S, some plumies, and a few hanging hoyas, I don't want to cram it full, but as much as I can possibly fit in there with still being able to walk somewhat comfortably.

Hi, Bec. Most of these greenhouses will come with 4mm twinwall polycarbonate. Assuming this glazing, you should be able to maintain, on the worst nights of the year, 63 degrees with two of the 1500W (5120 BTU) inexpensive milkhouse-type heaters that you can get at Walmart. One of these heaters won't be enough...one will keep you just at freezing. (An 8700W heater would be needed to maintain 54F.)

You won't be able to run both of these heaters at the same time on one standard circuit or by way of one extension cord. Each heater draws around 12.5 amps, so two would overload a 20amp circuit. If you would be running extension cords, then you would want to be sure they were plugged into outlets on different breakers.

You will have to ventilate, even during the winter, but that's a different thread!

One other thing...be careful in the placement of your heaters. I fried the foliage of a Washington Navel orange tree this winter after placing it too close to a heater fan. It has recovered, but with two such heaters in a small greenhouse, you'll have to be careful.

Hope this information is helpful!

SB

Thank you, that pretty much covers it. All I need to do now is get ordering, it obviously can be done, so I am doing it! I have lots of time left, we still have a few months until I even havta think about heating anything! Thanks again!

Excellent. Post back with some pics when you get it set up with some plants inside. SB

This was very interesting for me to read. Have been begging my husband for a greenhouse or even enclosing our gazebo,but he says a greenhouse to heat properly would increase our utility bill too much. He is an electrician and has read about this a bit. I am in zone 7b, similar to your zone in VA, but don't think our cold weather is as bad as yours. I am very curious to follow this thread on your outcome and - please - keep me posted on your utility bills !! thanks so much.

It is possible to determine ahead of time what your utility bills will be. You use the heating calculator, but instead of putting in the lowest temp (which will determine the heating capacity you will need), you put in the average temperature for a given month in your area.

So, using the greenhouse example above, holding a min temp of 54*F, and knowing the average January temp in Memphis is 41F, your heating formula (Q=deltaT*A/R) shows that you will average out over the month 2093 BTU (that's per hour). At 3.4413 BTU/Watt, that's 613W/hr. At 720 hours/month, that 441 KWH/month. At about $0.10/KWH, that's about $44.10 added cost for the month of January.

I apologize is there is a math error here, but you get the idea. I'm happy to help anyone with their own numbers or their own examples if needed.

SB

Good to know, I was calculating around $50.00 extra a month, so I wasn't far off! I have a few things I need to take care of and some payments coming in ( I work from home) ~ then it will be ordered! Am I right in calculating around $1500.00 to get started?

If we are talking electrical expenses/month here, don't forget to add in the electricity for cooling down the grhouse-I find thats what adds up for me.

If your grhouse is in full sun ( I hope it is) then you can count on having a fan on all the time, everyday that it is sunny out starting in mid March-give or take, and half the day during the winter months that it is sunny out. Grhouses heat up fast during the day.
Sb, whats the elec needs/costs for the fans? I know that I have huge ones, so they draw more per hr and that I have to have 220 in there. What about smaller fans?

I think our costs is about $ 0.13/KWH, and we have 2 nuke reactors here in this state ( for my elec company). I thought it was cheaper than other types of electricity??

Thanks for the idea of what mine might be based on the size that Bec is building. I think that is about what my DH was thinking. He keeps telling me if I ever want to quit work, I have to go by his motto - "less, not more". I just haven't gotten there yet.

For energy use during the summer, you just need to know the amps of the fans. I think my exhaust fan draws 4 amps. W=A*V and I run on 120, so the fan, when on, draws 480w. Multiply this by hours per day, say 12, and you get 5.76KWH/day. At $0.13/KWH, that's $0.75/day or $22.46/month. You can do the same calculations with your HAF fans and anything else running in the greenhouse, whether on 120V, 220V, 24VAC or whatever.

SB