To heat or not to heat

[Jeff S]

Last year I spent a ton heating my fish tank and built low tunnels around my beds to keep plant temps up. This year I'm thinking about heating the greenhouse to around 50-60 and by doing so cut down on the fish tank heating cost. I don't think this would cost any more than heating the tank in freezing greenhouse. I've taken additional steps to insulate the greenhouse and fish tank and have plenty of wood and a backup thermostatic propane heater when needed for when the fire goes out. Any thoughts on this concept?

[John Pink]

Hi  I have a propane heater ,they are as dear as fire is hot , This heater was  thermostatically controlled  ,two weeks the cylinder  needed changing - I didn't bother- far too  expensive  to run .Bubble wrap the greenhouse ,that would help .Some people use Christmas lights to heat greenhouse ,the other method ,put candles in a bread tin (tea Lights) four bricks ,place a clay  flower pot over- cover the drain holes over the top, add  another flower pot over the first one -quite effective.not sure you need the greenhouse as hot as 60 degrees? If you cut down heating the water in fish tank ,you might lose bacteria which are beneficial to plants. .If it is  really cold  cover the greenhouse with polystyrene . 

 

[Ian Cameron]

Jeff, have you considered a super insulated section of your greenhouse for your fish? The up front cost may be higher, but if you use wood for heating you can utilize water heating capacity in/on your stove and pump efficiently to a coil in your f/t. I did that last year, with a Ranco temp controller and a 12v hot water pump. Depending on the fish you are raising, you can set your f/t temps to fit. Are you running HID lamps? If a fan is mounted to the peak of your g/h, you can move the lamp heat around quite well. Again, I used a used 12v car rad fan to do this for me and it ran 24/7 for the entire winter. Sometimes you just have to experiment, and think outside the box.

[Jeff S]

The fish tank is covered with 1" Styrofoam and has a 1000 watt bucket heater in it. My theory was if I kept the GH warmer I wouldn't need to run the fish heater 24/7 at the same time enabling me to grow more vegetable types. I plan to keep the FT around 68F.

Ian: I have a thermostatic fan in the ceiling set to come on at 60F. I have 3 GBs each with a 400w HID light. I rotated t the on times of the lights last year in the low tunnel to add light and heat to the growing area. I'm considering the coil water heating but haven't done anything with that yet. We just got our first snow today and our first taste of winter coming up this week. Right now I'm able to keep the GH temp at around 55F running just 1 HID light when temps are 32F outside.

[Mary Hunt]

I'm in the NW with 30 degree nights and 40 degree days. (no direct sun during this part of the year) 

I insulated my 300 gallon tank using packing peanuts and 2 inch insulation and a plywood all around. I use two tube heaters - a 150 watt and a 350 watt. The water stays at 78 degrees if I didn't have it circulating through the rock filled trays. As soon as it does, the water temp goes to 69. I worry about stressing the fish with that much of a swing during 24 hours, but the black nile tilapia are eating well.  So far the 250 sq. ft. greenhouse is holding its temp at the set 55 degrees via a 220 wired heater. I'm sure I'll be donating a kidney to pay the heating bill.... 

[Jeff S]

I have Tilapia too and they survive just fine with all sorts of temp swings. When the water all went out in a plumbing malfunction (several times) I refilled with water as low as in the high 50s and they did just fine. I plan to run my tank at 68 this winter. I'm not that interested in growing the fish fast. I have way to many. I 've had huge pH swings, temp swings, ammonia swings, you name it and I've had it and the Tilapia do just fine. However, if you let the air run out that's a different story. Make sure your water and air pumps are on separate circuits if possible and that will eliminate that possibility as long as you don't loose all power.

FYI just heating the water 24/7 cost about $100 a month. The GH could be much more with electric. I'd suggest a gas radiant heater, natural or propane. Running 1 400w grow light is a big help plus you give your plants good light.

[Mary Hunt]

Thanks for experience lesson. Good to know that tilapia are hardier than advertised - still don't want to torture the little babies...  I hadn't considered the air issue, but will have a battery back up for that ASAP as we lose power often. 

I have 4 (4 tubes each) grow lights the come at 8 and go off at 6. I probably should run them for longer hours. It's DARK up here in the winter. Things are growing s l o w l y. This is my first winter experience with this greenhouse. 

Thanks again for kicking in some suggestions. 

[Jeff S]

I would shut the lights off during the day and capitalize on the heat they produce at night.  Those lights are like having a 500 watt heater running. My biggest problem with lack of air is my stocking density. The oxygen depletes quickly. In a regular stocking situation you should be good for several hours.

[Ian Cameron]

Mary, are you using insulation around your grow beds? I insulated mine with foil backed bubble wrap, not much, but it sure cut down om my heat loss from the ft. I also insulated all my plumbing  with this stuff. A few years in the far north oil and gas camps taught me where to save on heating costs, and this was one of the best.

[Mary Hunt]

Thanks Ian - The beds have 2 inch wood walls. I would think that would be enough, but perhaps not. The I have insulated the settling tank, but not the pipes. I'll give your suggestion a try, however, it's hard to imagine how bubble wrap could keep the water warm when it's coming in contact with 2 yards of crushed rock on its way back to the fish tank. 

Jeff - no can do with the lights on all night, the neighbors would get a bit miffed at the glow coming in their windows. 

[Jeff S]

I put a 1" piece of styrofoam over my rocks and cut holes in it for grow spots. This helps keep the heat in but makes it difficult to remove old roots unless you replant the whole bed. I think I'll slice the foam across the holes for easier removal next time.You might be able to place that bubble wrap between your plants to cut back on heat loss.

[Mary Hunt]

That's a thought. Thanks. 

Jeff S said:

I put a 1" piece of styrofoam over my rocks and cut holes in it for grow spots. This helps keep the heat in but makes it difficult to remove old roots unless you replant the whole bed. I think I'll slice the foam across the holes for easier removal next time.You might be able to place that bubble wrap between your plants to cut back on heat loss.

[dennis finnegan]

often people try to heat the Air in a greenhouse. This proves to loose heat fast .I know it is Winter now but if you plan well for next year you can add some thermal mass to your green house. This can be some part of the flooring with poured concrete (a sand mix will do ) with pex tubing in the concrete. and a propane boiler with propylene glycol or an electric high efficient boiler. I know this will have an up front cost but it will last Years if installed properly ,and you will not freeze the boiler (or heater )  due to the Glycol. Or it could be radiant panels along the outside walls. Insulation only works if there is heat in the greenhouse to begin with. The thermal mass will also pick up heat if the Sun hits it during the day and it will give up its heat at night. be sure to install a thermal barrier below the concrete to keep the heat moving up into the greenhouse.......that's all for now....this subject has a lot of matter and cannot be all covered today. If this interests you we can continue later.....Heydens Garden, dennis