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At a trade show today I met a man who installs paving block driveways. His driveways are heated so as to negate the need for plowing which could otherwise damage the paving stones. Popular on Manhattan rooftop gardens too.

The heating system utilizes water (with some additives) in a sealed loop system running through so me sort of poly type pipes. Like the radiant floor heat systems that go into new homes now. I couldn't help but think of Pumpkins when I saw it. When I asked about possible horticulture uses such as this, the guy freaked out.

The system sounds rather cost effective but before I spill the beans I'm curious what folks think a system like this would be worth to them.

The 110VAC hot water heater is a stand alone unit with a built in circulation pump. Distance from sheltered structure housing heater could be 30-50' to the patch so long as not much more than a 12' x 12' (144 sq ft) mound is to be heated. Shorter runs may be able to serve multiple mounds, though I don't yet know exactly what the systems limitations will be.

When this guy finishes his current $370,000 driveway (YIKES!), he wants to design me a prototypical unit ASAP. Even after explaining the rather "niche" maket we are, he still sounded interested thinking perhaps other similar applications might exist.

I promised him I'd poll my peers. LOL

So let's here it. Insane waste of time or possibly cool idea?

Steve

1/14/2004 7:44:54 PM

Rhode Island

steve next discussion would be depth and the amount of glycol pvc is not the most resistant to cold this would be relatively inexpensive to create an maybe more effective than heating cables

1/14/2004 7:52:22 PM

Key West, FL

cool idea but I think there are much easier and cheaper ways of heating soil

1/14/2004 7:59:06 PM

Key West, FL

Also, I don't think we have much of a problem with soil temperature out here.

1/14/2004 8:00:01 PM

[email protected]

I have done a lot of research on the water heating sustem.
It's quite simple actually. I picked up an RV water heater which runs on propane.($75.00) Then you need a 110 volt recirculating pump (new $89.00) Build 2 plumbing headers with 4 outlets on each, one for outflow and one for recovery
Cost of these headers is $18.00, The last thing you need is 4 100 ft. black 1/2" poly pipe.
The pipes are buried into the garden, I'm going in at 12" and I hope it heats as much down as it does up, The hoses are layed in trenches 24" apart. Each hose should heat 200 sq. ft. and you can heat 4 mounds.
You can use extra feeder lines to make up distance, but the most important thing is it keep all the pipes the same length, to maintain equal circulation. If one pipe is 10 ft shorted than the rest, it takes 75% of the circulation

1/14/2004 8:15:15 PM

[email protected]

I forgot to mention the pipe has a 25 year warranty when buried in sand, item 4 or cement. It is unlikely (according to him) that well amended garden soil would pose greater risk.

1/14/2004 8:15:29 PM

[email protected]

You can even use garden hoses if you wish. I'm not using Glycol because I'll pull it up in the fall and move the mound for next year.
Eddy

1/14/2004 8:16:44 PM

Eugene, OR

ice-man has the right idea to make the system economical for growers with small budgets like myself. The soil above the pipe will be warmer than the soil below as heat rises. That's not to say the soil below the heating pipe won't be warm as well.....it just won't be equal when compared to the top. Good idea not using glycol or a similar anti-freeze. I know how poisonous it is to humans, I can only imagine how plants would react to it if a leak developed in the soft poly. Tremor might be able to comment on its toxicity to plants?!?

One question I'm a little curious about. What are you using to regulate the temperature of the water in the lines, as well as to keep the heater from running all the time?

1/14/2004 8:45:37 PM

Montoursville, PA

There would seem to be no need to consider this down as low as zone 4. There is lots of time between frosts and then some using simple cold frames. If one thought a little heat was a plus a wheel barrow load of manure creates a hot bed which converts to humus. In the process all the other good benefits of using manures goes along with the effort.

Net cost in many cases is sweat labor.

1/14/2004 9:28:30 PM

[email protected]

Brian
Still in the test stage so I will know after this spring. The waterheater has a thermostat with it, that's no problem. I was going to put an inline thermometer to tell the temp of the water, I am thinking around 85 degrees, Which I should be able to regulate with the tank thermostat.
I wish I was in zone 4. I'm in Zone 3a, so I need to do something as last year, my ground temperature was 58 degrees on June 1st(at a depth of 12") I'd like to bring up my temp by 10 degrees

1/14/2004 9:48:38 PM

[email protected]

RV-Boat-Mobile Home antifreeze is plant safe & biodegradable. We use it to winterize spray rigs. Smells nice too so that the water tanks don't yield smelly drinking water the following spring. I'm not sure this is what he has in mind, but it is what I would use. One power failure during a preseason cold spell would destroy all the manifolds even if the pipes are resilient enough to handle some ice.

The hot water heater is thermostatically controlled just like any house type unit.

I don't think I would trust a garden hose to this application. The cost would actually be higher. And the threaded fittings & non-burial grade covers would be asking for trouble. A 25 year direct burial hose at lower cost represents a much safer & better value.

My new acquaintence says a finished system would sell for under $300, though as yet this remains to be seen.

1/14/2004 9:48:42 PM

Eugene, OR

Ok, thanks for the info on the anit-freeze. If I remember correctly, propylene glycol is the safe stuff.....I think!

Sounds like a pretty cost effective way to heat the soil. I guess the actual cost will depend a lot on how often the water heater has to cycle to maintain the temperature you set it to and how often you actually use it.

I sure wish the city here would get off their duffs and finish running the geothermal lines. Most of the bridges, roads, sidewalks, and state buildings are heated using the geothermal water supply we have here to keep the roads driveable in the winter. The water temps average around 220 degrees at the source. By the time it gets here it's quite a bit cooler, making it possible to pump it. Even with the drop in temps, it's still plenty warm enough to run through a heat exchanger to heat the house along with the pumpkin patch once it runs through the heat exchanger and cools off a bit. But like anything good, the government is not keen on sharing it.

Drooooolll

1/14/2004 10:02:47 PM

Wisconsin

I have a radiant floor heating system in my Wisconsin home that uses an inexpensive water heater to heat my entire home. It is a great system. There is nothing like warm floors on a cold winter day.

I don't see how this would be very useful with pumpkins though because in the spring it is pretty easy to get the soil temps in the 70-80 degree range with a plastic covered cloche (and sometimes black plastic on the soil). The real challenge is keeping the air warm above the ground during the cool nights. The soil would have to be hot (far over 70-80 degrees) to radiate enough heat upwards to keep the air warm. This would undoubtedly harm the root system. There are also much cheaper and easier ways to keep the air temps in the desirable range.

1/14/2004 10:51:06 PM

mcminnville oregon

mann!!!! i thought i was getting carried away by addinng a shop light to my cold frame!!!

1/14/2004 11:41:13 PM

Ga.

me too Dave!

1/15/2004 2:20:16 AM

Kenyon, Mn.

I think I'll do my whole garden!!!LOL MONEY, if ya got it,spend it!:) FEEBLE ATTEMPT AT SARCASM!! I thinks me cold frame will have a shop light!!

1/15/2004 8:12:32 AM

Indiana

Im gonna put a ceramic radiant reptile heater in my cold frame for my early pumpkin plant, it just screws into a lightbulb socket. The neighbors already think im crazy, I just wonder what they would think if I put a water heater outside to heat my pumpkin plants.
Steve

1/15/2004 9:51:35 AM

Utah

Tremor-
I think it is a great idea. I have see radiant floor heating systems on TV and wondered if they would work in the patch but didn't ever do anything more than wonder for a few minutes.
for $300 i'd seriously consider buying one...
how many sq. ft. are we talking here?

1/15/2004 10:17:56 AM

wilmington,ma.

What about a solor panel,they use them to heat pools??

1/15/2004 3:26:53 PM

White Plains, NY

Steve,

I have a roll of solar tubing for you. Put a circulator on it to a 1/2 inch hose system underground and you have heat.

1/15/2004 5:12:40 PM

C N Y

yeah, Tremor, great idea, and keep us posted on the
results and/or developments---it might be too costly for me THIS year, but i WILL have my car paid off eventually!'pal2

1/16/2004 1:07:29 PM