Oxygen loss is also determined by the temperature of the water. The warmer the water the quicker it loses oxygen and thus harder to keep oxygen in the water when the pumps are turned off. I have my pond ran off 1 circuit and use an in-line light switch that I can flip to turn off the pumps when I need to do a little maintenance or sometimes I need to switch it when its very windy outside so I don't lose a lot of water from my fountain and spitter. My pond is only a 50 gal pond so oxygen loss would take quicker affect on the fish and I have already went 2 days with my pumps turned off and never had a problem. If you are worried about oxygen loss for the 1 day you have the pump turned off you can add some fresh water to the pond to give it some oxygen.

[quote]R2 as we know it in America is quite low for house insulation. I used that number to allow for our test greenhouse to have 6mm twinwall on the south and south roof and some insulation on the North walls etc.[/quote] Heh, perhaps I'm just weird then, but I have metric R2 on my north wall (+parts of east and west, +underground) and about metric R 1.4 for the glazing. Metric R values are about 0.17 times US R values. [quote]I am sorry but many here with small greenhouses are infact coming as close to an hermetically sealed structure as possible. 10-20 tubes of calking... on a 6x8ft? [/quote] Well, it depends on what the caulk is being used for. I caulked my insulation on. Let me tell you, that takes a lot of caulk. Even if you seal up all of the cracks, I would be surprised if the small amount of circulation couldn't occur through things like: * The drainage system * Between panes of closed vents * Through the zipper or doorframe. Sure, a vent is a good idea. But we're talking about needing a very small amount of air indeed. [quote]Also in this thread nobody has mentioned the water. Unvented heater, sealed up as best you can, no air exchange. Adding CO2 by burning propane makes it wet in there too.[/quote] That is true. The moisture beads on the glazing and runs down to the floor; it's like a jungle in there (when I wear glasses, it's instant fogging when I walk in). I haven't grown any plants that are sensitive to moisture-related diseases before, but I've got some in the seedling stage right now, so we'll see if they complain. They're doing quite beautifully so far (I could get pictures if you like), but moisture-loving diseases like powdery mildew take some time to get established. I'll get back to you about them in a month or so and let you know how they compare to the equivalent plants grown outside this summer. [quote]stressbaby, Gladly. Greenhouse cucumber operation in Calif. with newly installed unvented heaters. After a cold winter period, severe damage was noted on the crop. Air samples analyzed showed elevated levels of ethylene and mercaptan.[/quote] Elevated *mercaptan* levels? Wow, that heater must have been doing an awful job. Mercaptans are only in PPM quantities to begin with, so if you're having measurable amounts *after* combustion, something is seriously wrong there. [quote]economic losses to greenhouse growers from ethylene pollution are reported each year[/quote] You do realize, I presume, that ethylene pollution can happen even when no heater is used. Decaying plant matter is an especially bad ethylene producer, but even healthy plants produce it (some species more than others). [quote]For an interesting thread from about a year ago, complete with more examples of problems with unvented heaters, use the search function, type "carbon dioxide" and read the posts on "plants suffering from propane". Some noted problems in other "real-life" situations.[/quote] Well, for your information, with Thanksgiving dinner, my main course was a delicious vegetarian lasagne made with a heaping handful of basil from my "suffering" greenhouse basil plants. Last night for dinner, I had pasta primavera made using some of my "suffering" tomatoes. My point? A proper installation doesn't have problems. An improper installation does. Notice how you haven't gotten into the risks of the other common hobby greenhouse heating system, electric. You know, a box of resistors with large amounts of current flowing through it, in a moist environment that usually has a metal frame, and plenty of combustables within, possibly even standing water? I read the "suffering from propane" thread before I got my heater. I read enough from elsewhere to realize that this person had an improper installation. Notice -- it only took a few days of use of their heater for problems to occur. Mine has been running for two months this winter. Note what was mentioned in the thread: "Sometimes the smell is very strong." Huge red flag right there. Properly combusted propane/natural gas has no smell. The instant they smelled it, they should have disconnected the heater -- it sounds like a leak. Note what others said in the comments trail, such as Orchiddude and trigger_m (who also provided pictures). [quote]One factor missed in this thread was ethylene.[/quote] Ethylene was already mentioned several times in this thread. Use your browser's search function; you'll find it.

Yea I have a Truncheon nutrient meter and have been using it / logging my findings - which have shown me that leafy greens don't eat too much :) I am about to top off the tank tonight with 3 gallons... seems like the plants are getting more thirsty recently... because the EC meter shows EC of 1.2 (600 PPM) I am going to mix nutrients with this added 3 gallons, as I don't want the nutrient to fall below 600 in the last week. I am also using the eco plus line of pumps, and the threaded adapters that you mentioned here are what got me thinking about what would happen if I mounted it outside the reservoir, but a little below the reservoir so it would always have a priming of water when it kicks on. Quote: " When i grew my office tomatoes, I filled a 5 gallon bucket with 3 gallons of nutrient for one plant. in the early stages, I used the same nutrient for somewhere around two months. Eventually, as the plant got larger, it started using more nutrient. near the end it was using one gallon per week. I'd start with 3, let it run down to one, fill it to three, let it run down to one, fill it to three, let it run down to one and change it out. (I think that was the cycle) all this time adjusting the nutrient level as needed. " Using the same nutrient for way more than one week - sounds good to me, wasn't sure if that was possible or not. I guess if the EC meter is showing it's still there, and there are no problem in the tank, I guess it's ok. Sounds good about how to top off nutrients and eventually change out just in case one nutrient is building to too high of a level. This is my only concern with something like the autopot - how to regulate nutrients / could you flush out / would you want to / etc. I'm having a hard time determining if I have nutrient lockout at all or not - can't tell what that looks like vs. what I think may be the thrive alive red laying on the bottom. But nontheless i'm going to top off this time since the EC pen says 600 PPM currently. I've been running a PH of 5.5 or so but I'm wondering if 6.0 is better for lettuce based on what I've read, so I've upped it. Thanks for the comments!

The hydronic solution for the basement is an excellent idea if this hydronic air-source HP system were to be installed. First of all, the HP is essentially a geothermal HP without the ground loop; commercial quality that even includes a desuperheater for domestic hot water and an electronic expansion valve for greater control and efficiency! I would suggest properly insulating the slab in the basement with 2 to 4-inches of blue Styrofoam sheets, installing closely spaced in-floor radiant throughout the house for a lower supply water temperature and hydronic fan coil units in the basement and elsewhere where you want quick control of temperature, dehumidification or air-conditioning. Hydronic fan coil units are designed with drip trays and in some cases with condensate pumps for the removal of condensate (water) in air-conditioning mode. This system configuration does not require a gas line, chimney, side vent or much annual maintenance. I would install buffer tanks for both domestic hot water and for the radiant heating and cooling for energy efficiency and to prevent short cycling when only 1-zone is calling for heat or cooling. This is a big house. Even with gas forced air they will still require large electrically powered fan coils to distribute the air. With in-floor radiant they only have to heat from the floor till about 6-feet off the floor. Who cares what happens above that height - remember, this is radiant! Forced air requires that you heat the entire volume of air within the envelope – a completely different animal! Haven’t even discussed the possibility of using chilled beams for air-conditioning that’s possible with this system. Heating without ducts, A/C without a fan coil – imagine that! Think Water! http://www.multiaqua.com/index.php/water-fan-coils/mhww-3-hi-wall-120v#mhww-3-installation-operation-manual http://www.multiaqua.com/index.php/water-fan-coils/cffwa-universal-2p IMPO SR