Tagged: greenhouse furnace

Greenhouse Heaters – Which One Is Right For You?

Greenhouse HeaterGreenhouse heaters. Electric, natural gas, propane and many more. But which heater is right for your greenhouse? How do you find out? This is where BTU’s (British thermal units) come in. To find the best heater for your greenhouse you must know the number of BTU’s required. And I am going to show you how to determine it!

Here are a few simple steps to find your BTU requirement.


  • STEP 1

You need to know the surface area of your greenhouse. This is not simply multiplying the length and width. You must calculate the area of each wall and each ceiling panel then add them all together. If you have a Sunglo greenhouse click here for Sunglo’s Surface Area Guide post.

  • STEP 2

Next you need to find out the average winter temperature (outside) in your area. This is where the internet comes in handy. But I made it easy for you > Click here to view a list of average temperatures in the U.S.

  • STEP 3

Now what temperature do you want to keep your greenhouse at in the winter? This depends on the plants you are growing. You should be able to find plant temperatures online. But a common minimum temperature for over wintering is 50°F.

  • STEP 4

The next step is finding your greenhouse’s U-Value or Heat Transfer Coefficient. This is determined by the material your greenhouse is made of. For a Sunglo greenhouse we use a U-Value of 0.75. To find your specific materials U-Value > Click here for a general list.

  •  STEP 5

Now that you have completed the first 4 steps you should have –

  1. Your greenhouse surface area
  2. Average winter temperature
  3. Desired greenhouse temperature for the winter months
  4. Your greenhouse material U-Value

Now we can find our required BTU’s!

And here is the formula –

  • Desired greenhouse winter temp – Average winter temp outside  = Temp differential
  • Surface area × temp differential × U-Value = Required BTU

For example:

My greenhouse surface area is 744

My average winter temp is 20°F

Desired greenhouse winter temp is 50°F

Sunglo acrylic U-Value is 0.75

  • 50° − 20° = 30° (Temp differential)
  • 744 (surface area) × 30 (temp differential) × 0.75 (U-value) = 16,740 BTU’s

Now you can shop for a heater that provides at least 16,740 BTU’s!












Building Your Greenhouse


 greenhouse contstruction


Early American Greenhouse History




We found in Google Books a scan of an interesting book from 1896, Greenhouse construction:  a complete manuaIllustration of the effect of greenhouse glass angles on sunglightl on the building, heating, ventilating and arrangement of greenhouses by Levi Rawson Taft, a professor of horticulture at Michigan Agricultural College.  Below is an excerpt from the book on greenhouse history.  While the information is dated, the book contains some interesting information and diagrams such as this illustration of the effect of glass at different angles.  From Chapter 1, Greenhouse Construction, History of Greenhouses:

It is known that the old Romans were able to secure fresh fruits and vegetables, for their banquets, the year round by both retarding and accelerating their growth. As an indication of their skill, it is said that they even forced the cucumber. They possessed no elaborate structures for this purpose, but grew them in pits covered with large slabs of talc. Heat was obtained from decomposing manure, and by means of hot air flues. They are believed to have had peach and grape houses, and it is claimed by some, that hot water in bronze pipes was used to warm them.

In modem times the structures have undergone a gradual development, from houses containing no glass whatever, to the forcing house of to-day which is nearly ninety-five per cent. of glass. The first house of which we have any record was built by Solomon de Caus, at Heidelberg, Germany, about 1619. It was used to shelter over four hundred orange trees planted in the ground, during the winter, and consisted of wooden shutters placed over a span roof framework, so as to form the walls and roof. It was warmed by means of four large furnaces, and ventilated by opening small shutters in the sides and roof. In the spring the framework was taken down. This structure, in size, compared well with the greenhouses of to-day as it was two hundred and eighty feet long and thirty-two feet wide. On account of the expense of putting up and taking down this framework, and of keeping it in repair, it was replaced by a structure of freestone. This had an opaque roof, and the openings in the sides were closed with shutters during the winter.

What’s great about reading through these older volumes is to see what has changed and what remains true about an efficient, functional greenhouse.  While they had no access to the modern materials such as the aluminum frames and insulated acrylic panels we use in our Sunglo Greenhouses, there is the same concern with durability, climate appropriateness, maximizing available sun and managing temperature.  We hope you have fun reading it!  And, if you decide not to build your own greenhouse out of wrought iron and glass, give us a call.