My 32ft by 54ft greenhouse just has one heater in a corner hanging from frame and pointing towards the opposite end. But it has two circulation fans to help the warm air circulate around the greenhouse. The bottom of my heater is 8ft up.

So location, height, and size of heater depends on many factors several of which you haven't specified. Is the frame strong enough to hang the heater up out of the way so as to not rob space? Why two heaters? Circulation fans? Crop and minimum temperature desired?

If you circulate the air, it doesn't matter so much where the heaters are. I think you see them mounted up high so that they do not take up valuable floor space.

Have you calculated an estimated cost to heat your structure? It's not going to be cheap. I put a link to a calculator below. The r-value of your double poly is about 1.4-1.7 and if the end walls are a single layer, that r-value is about .9 Make sure you inflate with outside air to avoid condensation between layers.

Most people are surprised by the amount of energy it takes to heat a greenhouse overnight. Clear material that good for making a greenhouse is always a poor insulator of heat.

Here is a link that might be useful: heat loss calculator

Has anyone tried compost pile as a way to heat the greenhouse. I saw the idea somewhere on the internet and I was wondering if anyone has tried it.

Since on the subject of location for heater & fan, can somebody give me your opinions on my situation. GH is 12' long, 10' wide, 10' tall. I can place the heater at a corner pointing to the opposite, diagonal corner. I have a 14" fan for circulating the air. Where should I place the fan? And is 1 fan enough, or do I need 2? Fresh air is from 4 vents at the roof.
Thanks,

This post was edited by newgen on Mon, Oct 6, 14 at 17:25

Angie0615 witch greenhouse did you buy from growers supply ? also what's your location ?

try this place to look at different types of heaters.. www.rimolgreenhouses.com/Commercial

newgen add 2 fans in the middle of the greenhouse on the east and west side, one pointing north and the other pointing south..

am about to build a heat sink using a bucket heater for horses and a circulation pump to circulate hot water through the plastic lines my plants are going to sit on 9 used only at night time 0 any suggestions or comments?

Hey z123.
Maybe no suggestions but i have the same issue. I consider to hire a company for my heating issue. Maybe you should do the same?! Does someone already hired someone to build a professional heating system for your GH?
Someone know specialists for this job? Or should i just ask "ordinary" air conditioning companies?
Just an example:
http://www.airconditioningnm.com/
http://www.trane.com/Index.aspx
http://www.r-zs.com/en

Hire a company that builds or at least sells professional greenhouses. Someone like Stuppy or possibly the Greenhouse Megastore. They probably have professionals on hand to design systems. But it's not that complicated. My 32x54 greenhouse has one heater and two circulation fans. I heat to about 39F which is 10F warmer than ave winter low and 40F warmer than extreme low. Given that and the heat loss calculator linked above you can size the heater.

A typical residential heating and air contractor won't know anything more than I do and probably less.

Mass retains heat. I have seen people on youtube taking advantage of this property by using black barrels full of water and gravel on their greenhouse floors to absorb heat during the day so that it can be released to provide warmth at night. Maybe you could utilize this concept in conjunction with your heater by placing the heater and thermal mass in close proximity of each other and centrally located in your greenhouse. In most cases that I have seen people use these types of systems they incorporate a number of barrels.

Check out this youtube video: https://www.youtube.com/watch?v=rUj-5k9YqGQ

Here is a link that might be useful: OkDirtWorks Website