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bgifford

Greenhouse Heating

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bgifford

Hello everyone.

I have a problem. I have built a Greenhouse this year to put all my palms and other tropicals in. It's about 16ft wide, 20ft long and 10ft high.  I am planning on installing eventually a 220/240V line or Natural Gas line but will not be able to get that done this year. So I will need to use 110V Heaters. Has anyone had experience and/or has some recommendations as to which heaters I should get? planning on keeping temps around 50-55F at night if possible. Greenhouse is insulated well especially around the End walls. The coldest it got here in Central KY last year was about 5F but only for a few nights. Most of the time the lows were in the mid 20's and often above freezing temps.

Thanks.

Brian

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jimmyt

Welcome to the show!  I commandeered this heater calculation from another website but it will give you an idea of how many BTU's you will need to heat a greenhouse.

SIZING A GREENHOUSE HEATING SYSTEM
To find the right size heater, follow this step by step guide to calculate the amount of BTUH the heater needs to generate for the greenhouse. As an example, let’s use a GrowSpan Series 2000 Commercial Greenhouse that measures 35 ft wide by 96 ft long.

CALCULATE THE TOTAL SURFACE AREA
First measure the end wall: 35 ft width x 14 ft (average wall height) = 490 (one end)
490 x 2 = 980 sq ft (both ends)

Next measure the roof. Each side of the roof measures: 18’ x 96’ = 1,728

1,728 x 2 = 3,456 sq ft total roof surface area

MULTIPLY THE SQUARE FEET BY THE U-FACTOR
 GrowSpan’s S2000 Greenhouse is covered with 8 mm polycarbonate, which has a U-factor of .62  

490 (one end wall) x .62 = 304

3,456 (roof surface area) x .62 = 2,143

ADD THE NUMBERS
304 + 2,142 = 2,447

MULTIPLY BY DELTA T (THE AMOUNT OF HEAT LOSS OVER THE LENGTH OF THE HOUSE.) WE WILL USE THE HIGHEST DELTA T NUMBER OF 70 TO ENSURE MAXIMUM HEAT CAPABILITY.
2,447 x 70 = 171,290

CALCULATE THE AMOUNT OF BTUH
With GrowSpan’s 93% efficiency heater: 171,290 divided by .93 = 184,183. This is how many BTUH are needed to heat the GrowSpan S2000 Greenhouse.

You can find greenhouse heater calculators all over the web. Do a google search.

I have a greenhouse too and I have used electric heaters, portable kerosene and portable propane heaters, and now a fixed propane heater.  The 120V electrics will work but will probably take several and they will run constantly just to keep the temp near 40 F.  At one point I had 4 running in my 30' x 48' x 12' greenhouse.  They could not keep it above freezing when the outside temp went into the low 20's (Zn 8b).  These were the typical Big Box store home electric fan forced floor heaters(1500 Watt).  I then turned to portable propane heaters which are far more efficient and supply higher BTU output.  I do not have natural gas supply as I am outside the city limits so I had to turn to fixed propane.  I have a 150,000 BTU ceiling fixed hard plumbed propane heater now and it will easily heat the greehouse.  For emergencies(such as running out of Propane in the big tank I now use a torpedo style kerosene/diesel fuel fan forced 80,00/120,000 BTU thermostat controlled rolling heater as a backup.  It can run up to 10 hr continuous and heats well, and does not put out significant fumes.  I would have bought this before the electric heaters if I had known then.  If you have 240V supply then your electric heater options increase greatly. 

jimmyt

Edited by jimmyt
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jimmyt

Also factor in the greenhouse material double wall,  glass, polycarbonate, polyethylene, as they all have different heat loss characteristics.  

jimmyt again!

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Trent

It's going to take a LOT of energy to sustain 50-55 degrees with outside temps below freezing using electric heaters. I used a medium sized single electric for example in my insulated garage to overwinter plants the last two seasons where outside temps rarely fell below freezing and could barely sustain low 50's.  Granted single heater, but also I'd venture far better insulated and generally warmer sharing walls with the house plus far less severe temperatures being a full climate zone warmer in 7b. This was with it running 24/7 for several months in an area similar in size to your greenhouse. I'd probably recommend 3-4 of the large HD or Lowe's heaters and expect to see a noticeable spike in your electric bill.

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jimmyt
4 hours ago, Trent said:

It's going to take a LOT of energy to sustain 50-55 degrees with outside temps below freezing using electric heaters. I used a medium sized single electric for example in my insulated garage to overwinter plants the last two seasons where outside temps rarely fell below freezing and could barely sustain low 50's.  Granted single heater, but also I'd venture far better insulated and generally warmer sharing walls with the house plus far less severe temperatures being a full climate zone warmer in 7b. This was with it running 24/7 for several months in an area similar in size to your greenhouse. I'd probably recommend 3-4 of the large HD or Lowe's heaters and expect to see a noticeable spike in your electric bill.

Absolutely Trent!  

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bgifford

Thanks everyone. I figured that it would take quiet a bit of energy to heat my Greenhouse if I would only use 110V heaters. I have been looking really hard at some things and what it would cost me to get a Natural Gas line run from the House to the Greenhouse. And will go with that. Might just have to find a way short term until the Guy gets out there to install it. 

Last winter I stuck a lot of my plants in my attached garage and it stayed always above 40 without running extra heaters. So if push comes to shove I do that again until I get the Gas line installed.

Thanks again everyone.

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The Silent Seed

I definitely would commandeer the garage again - You do not need the headache and huge bills that come with heating a (plastic) greenhouse. 

The money you would spend in heating it would serve you much better going towards the new heating system. Save your thousands (not pennies.) 

Additionally, when all is said and done, I would love to hear what system you end up putting in, and what the real cost is to heat it, when that time comes. 

Edited by The Silent Seed

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bgifford
On 10/2/2019 at 9:48 AM, The Silent Seed said:

I definitely would commandeer the garage again -

I might actually have to do that since I will be gone on vacation in November and don't want to worry about my plants being possibly exposed to temperatures that might be harmful without me being able to intervene.

I will use this winter to get everything organized so that I can operate the greenhouse for the next winter.

 

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The Silent Seed

Perfect plan - better safe than sorry! And - have some in the house for enjoyment, if you can! 

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PlantDad

what you can also do is have a compost bin in there and really step up the composting. the heat generated can keep it above freezing. my grandfather has a decent sized greenhouse and keeps it above freezing year round in our zone 8b climate just by composting. he keeps jade plants and aloe vera and various frost sensitive plants in there all year. 

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bgifford

So I moved everything in the Garage these last few days since we will be running more and more risk of frost and freezing temps. I figured I would use this winter to make sure everything in the greenhouse is ready for next winter. Now I have a lot more stuff in the Garage this year than I have ever had. I guess I let everything go dormant. Reduce watering to a minimum I guess.

Does anyone have any tips for Garage storage? Last year all I had in the Garage were my Banana plants. Kept the Palms in the house but I added a lot this year to my inventory. So no real experience here with keeping Palms in the Garage. 

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jimmyt

Can you keep the temp above freezing in the garage?  Does the garage have natural lighting?   Those will be your 2 main hurdles for overwintering.  Yes you would have to significantly cut back on watering during the winter.  Depending on your plants some do not like temps even into the low 40's for any significant period of time.   I assume you dug the banana plants and just overwintered the corms.

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bgifford

Yes. Temps never get below 45 really in the Garage. There are two south facing windows but and I keep the Lights in the Garage on during the Day to help and was thinking about spot grow lights for the ones the might not get enough light. Hope that helps. Plus on nice days I was thinking about keeping the Garage door open on nice days to get Sunlight in there.

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GottmitAlex

I don't know the combined wattage of your grow lights. That said I would invest in a 120 watt LED 5000-6500k "corn" bulb with an e39/e26 adapter.  That's all the light the palms would need.

Like this:

https://www.amazon.com/dp/B07MC8PV4K/ref=cm_sw_r_cp_awdb_t1_g6mQDb1BED4HN

Heat is a different matter...

 

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bgifford
On 10/17/2019 at 4:27 PM, GottmitAlex said:

I don't know the combined wattage of your grow lights. That said I would invest in a 120 watt LED 5000-6500k "corn" bulb with an e39/e26 adapter.  That's all the light the palms would need.

Like this:

https://www.amazon.com/dp/B07MC8PV4K/ref=cm_sw_r_cp_awdb_t1_g6mQDb1BED4HN

Heat is a different matter...

 

I have two of these already. Will put those in there and put on a timer. 

Thanks for all of the advice on this.

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