I am in the same area you are, and started out last year (my first GH) with a 1700 watt heater. Hubbie spent alot of time caulking, also. After a $250+ heating bill in January, we had to do something!! Purchased a heater that attaches to a regular propane tank that worked well as supplemental heat. Think it cost about $45.00 which is a plus. The negative is we constantly had to fill up the tanks plus, every night, go light it and in the morning, go turn it off. This year we bit the bullet and put in a blue flame vent-free gas heater, as our main heating source, with the electical heater if temp goes below 54. We are renting a 100 gallon propane tank from the gas company. So far so good. You may want to scroll down several pages on this site, as this question has been debated for quite some time. Good Luck!

Get some inexpensive foam board and (Velcro) put them outside of the GH at night, or the shady side of the GH, very effective in keeping the GH warm.

dcarch

Appreciate your thoughts on this, but I'm trying to find out if there's any difference in a $25 vs a $100 heater when both are 1500 watts. What makes one any better than the other for the price difference? Or is the difference just in quality, name brand or what?

Propane is not an option right now and we're nearing a point where we've done about all we can do as far as insulating. Thanks!

Have you used bubble-wrap inside your GH? Calking alone isn't going to do it. I'm in TN and did the north wall, 3/4s of the roof and both sides of my GH with this stuff. It still takes 3 small 1500w heaters to keep it at 60F through a 20F night. Above 30F and two of the heaters do the job.

A man at HD told me the difference in price is because of quality. The more expensive heaters will outlive the cheaper ones. That makes sense. :)

All 1500 watt electric heaters produce the same amount of heat. The difference is the quality of the thermostat, the heating elements, fans, etc.

"I'm trying to find out if there's any difference in a $25 vs a $100 heater when both are 1500 watts."

I agree with Cuestaroble, it will be the same amount of heat.

To answer your question:
1. Some heaters are noisy, if that's important to you.
2. Ceramic heating element is better.
3. It gets dirty at some point, can it be cleaned easily?
4. Must have - shut-off switch when it is tipped over.
5. You probably should not plug in more than one heater per circuit (breaker).
6. If you get two 1,000 watt MH/hps lights, you get 2,000 watts of heat plus free light to grow lots and lots of stuff.

dcarch

I found this heating calculator helpful when trying to figure out how many BTU's it would take to keep my HFGH 10x12 at the temps I wanted. I read a 1500 watt heater would provide (roughly) 5000 BTU's, so once I had the total number of BTU's needed, I could determine I needed two 1500w heaters to be on the safe side for our coldest nights.

I bought two $40 1500w Honeywell electric heaters from Walmart, in the $40 range...hoping they'd last longer than the $20 ones, but figuring I probably didn't need to buy anything more expensive.

Thanks, I have zero experience with this and just wanted to understand what I'm dealing with here. It's amazing the things we've learned about in doing this!!

The Heating calculator is very useful. Keep in mind the following additional factors:
1. Wind conditions will have a major impact to heat requirements.
2. Ground temperature will need to be considered.

dcarch

I was thinking about putting some indoor/outdoor carpet (leftover from my daughter's wedding) on top of the 4 inches of gravel. It wouldn't cover all of it but should cover all but along the edges. Would that help insulate the ground temp?

Marginal benefit. If you look at a GH BTU calculator, none of them factor the floor area. This is because there is virtually no heat lost through a GH floor. Studies show some 50+% of heat is lost through the roof, 2-3% through the perimeter, none show loss through the floor.

Energy-wise, you are way further ahead with bubble wrap on the roof, 1" of polyisocyanurate foamboard on the north wall and north roof.

SB

Really? That's interesting! I guess it must be my imagination that the ground in there seems cold. Strange how that works.

My doors are in the north end of the greenhouse. We're planning on using the foam board for that. Thanks...

Here is the thinking:
1. Depending on the color and material of the GH floor, and solar exposure during the day, the mass of the ground can store a great deal of heat and releasing the heat back later on.
2. Heat transfer thru ground is significant, that's why you insulate basement walls.

dcarch

So far with my HFGH 10 x 12 with weatherstriping on the panals instead of calk I have been using a 1500 watt electric heater (while I have been waiting on Amerigas to have the 100 gal tank and lines inspected by the county)it has been keeping the GH 12 to 14 degrees warmer then the night time lows. I have a remote sensor inside and one outside. I am just east of Richmond, Va if that helps.

My opinion on the heat loss from the floor is it probably is just a small % that is lost, due to the greater cold gain that is there coming from the ground. Warm air will rise to the top so it will be lost from the roof. There is less warm air at the floor to be lost but it is going to be replaced by the cold floor air if it is not well insulated.
Of course it is only my opinion.

Here is a link that might be useful: my overkill foundation

Not over kill at all. It's a very good idea that you had insulated the floor. In zone 7, ground can get frozen down to 36". Yes, Hot air rises, when that happens, it creates a constant convection current. Imagine how many BTUs you will need to warm up 3' x 10' x 12' chunk of solid earth.

dcarch

There is a difference between insulating the perimeter and insulating the floor. I might disagree with dcarch on this...you do lose some heat through the perimeter, but heat lost through the floor is negligible.

Think about the temp differentials...the differential between the outside surface soil and the inside might be 30-40 degrees. That differential results in heat loss through the perimeter. But unless you keep you keep your GH unusually warm, there is a very tiny differential between the inside GH temp and the temp of the soil straight down...thus little heat lost there. Put another way, that 10x12x3 chunk of earth won't lose heat straight up, and it won't lose heat straight down, it will lose heat out the sides, on the perimeter.

Now with a smaller GH, the ratio of the perimeter to the surface area is relatively greater than in a larger GH...so the heat lost through the perimeter is relatively more important.

In any event, jba3fan, you have sort of combination of floor and perimeter insulation there. I'm sure it will work well. The standard recommendation is to bury 2" of perimeter insulation vertically, straight down, around the outside...lots of digging, lots of work!

SB

Sressbaby,
That is exactly what we did here in zone 4. We buried pink insualtion board around the perimeter of the base as you said. I hope it helps at least a little.

Oh yeh? You wanna fight with me! My daddy will beat you and your daddy up in two seconds! :-) :-) :-)

1. There is no such thing as too much insulation. There is such a thing as too much money and too much work to put in extra insulation.
2. The earth around the GH is the same as the earth inside and under the GH in terms of heat conductivity (heat lost). You don't generally try to keep the floor warm because it is too expensive due to heat lost straight down. Yes, a cold floor will not lost that much heat because it's cold to start with.
3. If you insulate the floor, you can then affort to, say use solar heat gain, at about 240 BTU/hr/sq ft to warm up the floor. I would think a black floor, 24" thick, with 2" insulation under can significntly reduce GH temperature swing from one extreme to the other.

dcarch :-)

Stressbaby, I am sure you mean 2 feet of insulantion instead of 2 inches in your post above. I know what you ment but someone else later on my not. (gesh I am the last person in the world to corect someones typos lol)
Time and money is really hard to define.. sometime it is the same having more or less of either. It took me about 10 to 12 hours to put in my foundation. I needed about half dumptruck load of gravle anyways for a raised bed I will be puting in this spring, so the delevery charge was going to be the same for 10 tons or 20 tons, may as well max out the delevery.

If I was to pour a slab floor for a heated area, by code I have to have 4 inches of 1 inch thick styrofoam insulation arround the perimited and 2 feet of 1 inch thick styrofoam inside of the perimiter. The codes in my area are different then other areas so people should do whats needed in their area.

I respect everyones opinions and their usefull information that is shared here.

Jim

C'mon dcarch, you wanna go? You and your daddy, both! ;-)

Ouch, I sound like my 14 year old!

Seriously, Jim, I meant 2" thick foamboard (I think that gives R-6 or R-7), and yes, 2' deep or more.

SB

rootdigger:
I've used Kersosene for several years now, and got tired of the odor, and having to refill every week. It was a hassle, so I searched online and found the Dayton 240V heater. This is the first fall/winter i am using it. It's actually not that big but it keeps the greenhouse around 45-50 on a very low setting. In fact, it went down to 19*F a few weeks ago, and it kept the greenhouse about 43-47*F on the same setting. The electric bill will probably be higher, but i don't want to keep running to the gas station to fill up the kerosene tanks anymore. Just have them on hand in case of a power failure. I've tried the 1500 watt heater last year in the greenhouse, and it didn't even make a dent in the temperature.

The heater i have is a 4200Watt-5600W heater which low setting is about 10,000BTU where high (5600W) is 19,000 BTU. When it drops below the pre-set temp, it automatically turns on, and when it reaches the max on that setting, it shuts off, just like the home furnace. The thermostat doesn't tell you the temp settings, i just experimented on low first and watch the thermometer to check what range the heater will run.. Good luck any questions let me know..
Steve