# Greenhouse heat question



## Duck Slipper (Aug 19, 2021)

Talking with a retailer about a thermostat and they did not carry a thermostat with the capability of setting back the night time temperature. What brand-model is used by STer’s with a greenhouse? Am I wrong by requesting such a thermostat.
Retailer said he had never had such a request.


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## Bob in Albany N.Y. (Aug 19, 2021)

I tried to use regular old house programmable thermostates for a number of years. Due to the high humidity I had to keep a couple extras on hand as they would stop working. Had to change them at least once or more a year. Luckily, my greenhouse is attached to my house so was able to buy one that stayed in the house with just a lead going into the greenhouse. It's a robertshaw. 9701i which is there deluxe programmable thermostat and I think the sesor was a 90251. I think that Robershaw may have sold the rights to the product to another company but don't quote me on that. I hope this information helps you as it took me years to find this product. Give me a holler if you have any other questions, as I'd be glad to help.


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## Duck Slipper (Aug 19, 2021)

Thanks Bob…maybe some others will have input about this.


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## Ray (Aug 20, 2021)

I am a firm believer that greenhouse thermostats should be set to the minimum only, letting nature do the daytime warmup.

If you are striving for a “nighttime setback”, it implies you are intending to use the thermostat to boost the daytime temperature, which you should not do; let the sun do that. Plant metabolism is closely tied to temperature. If you warm the greenhouse when there is little sunlight, the plants will be leggy and weak.

I do recommend you use a “remote bulb” thermostat, that is out in the airflow within the structure, rather than being up against a wall.


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## Duck Slipper (Aug 20, 2021)

Wow…I’m surprised to learn this.


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## richgarrison (Aug 20, 2021)

I have been using this thermostat from honeywell for 2 years now... TH6320WF2003/U

they offer a remote (hardwired) temp sensor that i have judiciously located out of the sun and heavy air movement.

it has a lot of sexy features i don't use, however i do use the day night temp feature to get the day temps to my desired minimum, and run cooler at night... It also is wifi enabled so that i can monitor it remotely... (yes i have called kids/neighbors when some anomalies have occurred ;-) - like the first week i installed it and then had to travel...)

As Ray mentioned, the sun adds the heat to boost day temps when the suns out, but since i have a hundred or so vandas in there, i want the day temps to bottom out around 72. and i let night temps fall to 68ish in the middle of the greenhouse stuff around the outside varies based on heat loss through walls/glass etc..


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## Ray (Aug 20, 2021)

I had my thermostat set to 55F. In single-digit days in winter, if the sky was clear, it would easily climb into the 80’s.


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## abax (Aug 20, 2021)

DS, are you concerned about summer heating in your GH? I never use one in the
summer, but I think my thermo is Dayton...maybe. I'll look tomorrow to make sure,
but I've had it for years working fine. Summer heat is controlled by shutter exhaust
fans, bench fans and three cool mist humidifiers behind the bench fans.


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## Duck Slipper (Aug 21, 2021)

No Abax, summer heat will be another entity in itself, and I don’t think I will have to worry about it till next year. 
Ray and others have had GH’s. To me, many cloudy days in a row, with 20-30 degree Fahrenheit temps and a thermostat set at a minimum temp of 60 degrees or 55 as Ray states above is inviting bacterial and/or fungal issues. I’ve also been of the belief that many orchid species need a cooler night temp. I understand sunshine will warm the house in the daytime…but there are many days the sun doesn’t shine AND is low on the horizon.


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## Duck Slipper (Aug 21, 2021)

Thanks for everyone’s input, I appreciate the help and I’m still interested in other opinions…


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## Duck Slipper (Aug 21, 2021)

Bob in Albany N.Y. said:


> I tried to use regular old house programmable thermostates for a number of years. Due to the high humidity I had to keep a couple extras on hand as they would stop working. Had to change them at least once or more a year. Luckily, my greenhouse is attached to my house so was able to buy one that stayed in the house with just a lead going into the greenhouse. It's a robertshaw. 9701i which is there deluxe programmable thermostat and I think the sesor was a 90251. I think that Robershaw may have sold the rights to the product to another company but don't quote me on that. I hope this information helps you as it took me years to find this product. Give me a holler if you have any other questions, as I'd be glad to help.


I have found Robert Shaw thermostats. What minimum daytime temp are you using in your GH?


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## Bob in Albany N.Y. (Aug 21, 2021)

I change my min. temp. I start out at 50 degrees, when summer is getting over (Oct). Then try to leave it there for a couple of months. Then I put it at 55 for the rest of the winter. During the day I have it go up to 63 degrees. That would be from around 8 a.m. until 5 p.m. Then it resets to the night temp. I know that Ray and many others state how fast their temps. go up in the winter. Mine do not. On the few days that we have with sun (Feb, and March) I'm able to open my top vents with a hit of a switch. That cools things off very fast. Then I just close them and turn off the power to them. I keep my shade cloth up year round. Hope all this makes sense to you. If not you can P.M. me or we discuss it here. On the days that I water, I boost the temp up to 70 until things dry off with the four fans always running 24/7. One important thing to mention that has nothing to do with temp. is to ALWAYS have a backup power supply that will come on atomaticly if your main heater fails. I heat with oil but have a gas backup furnace set just a couple degrees below my min. temp. It can save your whole collection.


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## abax (Aug 21, 2021)

DS, I was quite mistaken about my thermo. It's actually Schaefer and I couldn't see
the modern number. I've had it for more than 10 years. My set temps. are 55F night,
70 day, off in summer.


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## Ray (Aug 22, 2021)

Duck Slipper said:


> To me, many cloudy days in a row, with 20-30 degree Fahrenheit temps and a thermostat set at a minimum temp of 60 degrees or 55 as Ray states above is inviting bacterial and/or fungal issues.


Not at all, unless you are sloppy with your watering and cleanliness. There is nothing inherently risky about a plant being at its minimum temperature for days at a time, as the weather dictates. You won’t want to water then anyway, or you will leave pockets of water standing around that will invite infections.


> I’ve also been of the belief that many orchid species need a cooler night temp.


First, that contradicts your last statement. Second, every greenhouse I have ever had, no matter the size, has had several “zones” of different temperatures. In my 55F greenhouse in PA, even with fans running constantly, I had areas that were cooler - lower, nearer the glazing or door, etc. Once the greenhouse is operational and full of plants, you’ll likely see something similar.


> I understand sunshine will warm the house in the daytime…but there are many days the sun doesn’t shine AND is low on the horizon.


That is true, but so what? With low light levels and relatively low temperatures, the plants will grow very, very slowly, if at all. If you boost the temperature artificially without there being sufficient light, you’ll force the growth of weak, leggy plants. If your climate is such that you will have a lot of those days, you may need to provide supplemental lighting. Warming the plants is not a substitute!


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## JustinR (Aug 22, 2021)

Where I live (in Holland) with the low Winter sun there isn't enough of a boost to give the day/night temperature difference that many species need. I tried one year without the day time boost and lost quite a few plants, so I guess it depends on your individual situation. I grow 15 degC min with 21 degC day time boost for about 8 hours in Winter. 

I'm now using an Inkbird day/night thermostat, I think it might be available via Amazon or you can buy it direct on their website (from Chine) although I have to say that it's not that reliable (it cut out a few times), so a back up is essential. Before that I used two heaters connected on one of those washing machine / dryer switches with a timer on one heater. Be very careful when installing electrical equipment in your GH that you do so safely


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## Duck Slipper (Aug 23, 2021)

Well, after contacting Sam Tsui at Orchid Inn he answered more than one of my questions. My original question was “what kind of thermostat was being used by other ST greenhouse owners”?
Sam uses a regular home type thermostat that is programmable. The sensor is mounted in the GH, with the actual thermostat mounted in a remote location. This is a household type thermostat that does not have to contend with the moisture and humidity issues in a GH.
As far as the temperature settings, a warmer daytime temperature and a lower setback night time temperature his GH heat is at a comfortable 72 degrees Fahrenheit during the day. His nighttime temperature is 55 degrees Fahrenheit. 
Thanks for everyone’s time in answering. It is difficult to find an affordable 24 hr. programmable GH thermostat that holds up to the rigors of a GH. Still interested in others answers. Thanks again. Duck


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## cnycharles (Aug 23, 2021)

I don’t think that people who have never lived in a cold cloudy northern environment realize just how necessary it is to be able to boost your day temp to make up for heat loss from the bottom of your area (frozen ground outside) and at the edges of your house (microclimates). At the ‘minimum’ setting left all the time, your edges and bottom will be a lot lower than the minimum, as it gets colder and darker outside. Often it’s necessary to provide extra heat to balance the cold chill pulling heat away from your plants. This is likely semantics, since anyone can see it’s colder and on certain days bump the temp a few degrees. Anyone should be monitoring every day anyhow when it’s that cold. So, have to decide how necessary it is to program a difference, or just check things and turn it up a few degrees if needed


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## Duck Slipper (Aug 23, 2021)

Agreed Charles!!


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## Ray (Aug 24, 2021)

Precisely why we have zones within any structure.


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## LO69 (Dec 3, 2021)

I have not direct experience with such a problem but I once visited the biggest phalenopsis producer in North Italy (Padova) a place with many overcast winter days. They grew phal so warm days were a must have. They balanced the low light conditions and the need for warmer temp.with HPS lights.
Have a book that suggests the same thing.
Hope It helps


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