hot water heating

[awalker1106]

Hi -- I am getting back into orchids after 20+ years of child rearing. I am building a new greenhouse and would like to use hot water under bench root-zone heating. Does anyone have experience with this system? I live near Sacramento where we rarely experience sub-freezing temperatures, but it is normally damp,foggy and cold (40-45F) from November to March. Thanks for any advice. Andy

[Charles]

I think you may be in a position to teach the rest of us a thing or two about heating.
Please tell us more about hot water under bench root-zone heating.
I live in Florida and my winter weather sounds a lot like yours.

[Charles]

I am beginning to see your point now.

Although boilers and traditional hot water/steam heating systems are not used extensively in this area, there is a variation of these systems that is becoming increasingly popular among Texas growers. The use of hot water for "under pot heating" has been proven to be extremely effective and efficient. In these systems, water is heated in a modified hot water heater and pumped through an extensive tubing system that is mounted to the bench. The heat is radiated from the tubes and absorbed by the pots that are placed directly on them. The media in the pot is maintained at a constant temperature which allows air temperatures to be held much lower than with traditional systems. The overall effect is improved plant growth and reduced energy costs.
Greenhouse Heating Requirements

[awalker1106]

Hi -- "under pot heating" is what I am after. I know it is used effectively in the nursery industry for germinating seeds and rooting cuttings and for general liner growth. But I am wondering if there is enough heat to circulate in and around the foliage of taller plants such as large vandas and anagrecums. The system would save lots of money and is relatively inesxpensive and low-maintenance. Does anyone use it with orchids?

Thanks, Andy

[camille1585]

The horticulture university I was at 2 years ago in France used the under pot heating system in their greenhouses for the entire growth period of their plants. Some of these were quite large plants, like geraniums or cyclamen. But in colder weather they did couple this system with a classic heating system to make sure that the top of the plants were getting enough heat. In any case, they got better plants more quickly than simply using a heated air system. But unfortunately they did not do orchids, so I don't know how under pot heating works with full grown chids. Hopefully someone else on the OB will be able to give you the info you need!

[weng]

I live in England where the temperatures are a little lower in winter. I know of no one who uses such a system - the closest being running hot water pipes under the orchid bench.

It sounds like a good idea, but how do you avoid cooking the roots?

Weng

[camille1585]

I think that the system is realtively unknown to people, and it is used almost exclusively by professional GH growers. They use it essentially to lower heating costs and have faster growth (and save even more money!).
The water is heated to about 150°F (I think!! ), but it doesn't burn the roots since the plants are receiving heat radiating from the pipes(and not the hot water itself). The actually temperature of the air is probably around 70-80°F.
The advantage of such a system is that the air temp around the plants is steady and uniform, and the heat is where it is needed the most.I heard that 50% of the heat a plant needs should come from underneath, and the rest from above/around. Plants heated from below normally can tolerate a lower air temperature above.

In a small greenhouse I don't know if it would work since the air has less inertia. If your GH gets cold because of a sudden cold snap, radiated heat from the pipes will take a very LONG time to raise the overall temperature, and the poor chids will be cold! I guess that's why people recommend to use a forced air heater as well....