Axiom Posted March 19, 2023 Share Posted March 19, 2023 I am using underfloor heating like many others here, but I seem to have gotten some really powerful ones (200W). They worked great for a concrete floor within the insulation underneath the mats. The issue I’m having is figuring out what kind of material I can use to protect the bottom of pots and trays from excessive heat, and at the same time, not deflect heat elsewhere. I guess I’m trying to diffuse the heat so that it’s more constant, and even rather than bursts of very hot and then cooling down a bit. Admittedly, I wasn’t sure how hot the wires would get considering I’ve only ever used seedling heat mats before, and they are nowhere near as hot in comparison. I tried to use underlay for flooring, but that was a pretty stupid idea as quite quickly I learned that it had melted through completely. (-£17) I’m thinking of using a very thin sheet of polystyrene or insulation board, which will probably be uneven as it rests on the wiring. Maybe I could use layers of cardboard? You know... recycle and reuse etc.. Any ideas? Link to comment Share on other sites More sharing options...
Brysee Posted March 19, 2023 Share Posted March 19, 2023 How about using some old grill racks or something similar so you can sit them on the rack and it lifts them a inch and allowing the heat to still do its thing I have a couple mats then a 1 big tray sitting a inch on top of them working well for me 1 Link to comment Share on other sites More sharing options...
Wacky Wardrobe Posted March 19, 2023 Share Posted March 19, 2023 You can use one of those plug in dimmer/ speed controllers to reduce the temperature the heater reaches. I've used them on heat mats and a cabinet heater. Watch the wattage though. The ones I use are ok up to 300 watts only. You should be ok at 200 watts. 1 Link to comment Share on other sites More sharing options...
purepotstill Posted March 19, 2023 Share Posted March 19, 2023 If you have a big tray inside covering the tent's surface, you could put some sand in. It will diffuse the heat and act as a buffer. I won't put cardboard on something getting hot, but that's me. BTW, mine is 150W for 1m² and stays warm but never overly hot. Is yours as hot as you won't touch it ? 1 Link to comment Share on other sites More sharing options...
KC Posted March 19, 2023 Share Posted March 19, 2023 Does it use a normal 3 pin plug? If so just get a rootit thermostat, they're rated upto a 1000w I believe. It doesn't have to a Rootit one, I'm sure there are others but they're not expensive. 2 Link to comment Share on other sites More sharing options...
purepotstill Posted March 19, 2023 Share Posted March 19, 2023 Didn't even think it could come without a thermostat. 1 Link to comment Share on other sites More sharing options...
Axiom Posted March 19, 2023 Author Share Posted March 19, 2023 2 hours ago, Brysee said: How about using some old grill racks or something similar so you can sit them on the rack and it lifts them a inch and allowing the heat to still do its thing I have a couple mats then a 1 big tray sitting a inch on top of them working well for me Hmm yeah thats got me thinking of using old wood from garden trellice. Might needs sanding down or whatever but then again using rotting wood in the groom sounds risky. I guess could disinfect it. I've got spare grill racks actually but they're different sizes and won't fully cover the space. Just now, KC said: Does it use a normal 3 pin plug? If so just get a rootit thermostat, they're rated upto a 1000w I believe. It doesn't have to a Rootit one, I'm sure there are others but they're not expensive. Yes, its already got a thermostat with a probe. I've got the probe placed halfway down my fabric pots. I'm thinking making a hole right at the bottom and setting the temp to about 22 might solve the issue. I measured the bottom of a pot yesterday and it was 38c while the probe was reading a cool 20. I guess probe placement is an art form. 2 hours ago, Wacky Wardrobe said: You can use one of those plug in dimmer/ speed controllers to reduce the temperature the heater reaches. I've used them on heat mats and a cabinet heater. Watch the wattage though. The ones I use are ok up to 300 watts only. You should be ok at 200 watts. Can you link it for me or let me know the product name and where to find it please? this sounds ideal for the otter months and if it doesn't break the bank definitely worth it for constant root temps. 32 minutes ago, purepotstill said: If you have a big tray inside covering the tent's surface, you could put some sand in. It will diffuse the heat and act as a buffer. I won't put cardboard on something getting hot, but that's me. BTW, mine is 150W for 1m² and stays warm but never overly hot. Is yours as hot as you won't touch it ? Can you give me a lift to the seaside? Can't touch it, it will cook mi sausage fingers. 1 Link to comment Share on other sites More sharing options...
purepotstill Posted March 19, 2023 Share Posted March 19, 2023 Just now, Axiom said: Can you give me a lift to the seaside? You can find some sand in any hardware shop, don't you ? It's often needed for doing some work in houses, you can find some 20lbs bags, or even fill a few buckets from bulk. They sell some in some garden centers too. 2 Link to comment Share on other sites More sharing options...
Axiom Posted March 19, 2023 Author Share Posted March 19, 2023 @purepotstill So you mean put the grow trays / saucers in a slightly bigger sand tray with the heating mats at the bottom underneath? Sounds good actually. - except the sand tray would probably melt a bit too? I've had the heat mat wires directly under Gardland trays.. It warped the plastic a tiny bit (grooves form the wiring) melted in but not much at all. Any sign of melting plastic is a cause for concern, though as nobody wants their plants breathing plastic fumes. I like the idea of a wood / metal mesh type contraption. Old wood bed slats or something. Link to comment Share on other sites More sharing options...
purepotstill Posted March 19, 2023 Share Posted March 19, 2023 I'd make a tray-sand-heat mat-sand sandwich. 2 Link to comment Share on other sites More sharing options...
KC Posted March 19, 2023 Share Posted March 19, 2023 Sounds like a lot of wasted power, I think the roots like a gentle heat not a full on cook. I'd say your thermostat is fucked. 4 Link to comment Share on other sites More sharing options...
Clubs Posted March 19, 2023 Share Posted March 19, 2023 I use a piece e of capillary matting then put the probe through a hole in the bottom of the pot. 3 Link to comment Share on other sites More sharing options...
purepotstill Posted March 19, 2023 Share Posted March 19, 2023 (edited) Well, you don' really lose power because the sand will stay warm for a while after being heated, and even take some. But a fucked thermostat is credible, I wouldn't want a heat mat to get so hot I couldn't touch it. Edit : I make a pre-hole in the soil with a bamboo stick before putting the probe in. Works good enough for me, but my mat never get this hot. Edited March 19, 2023 by purepotstill 2 Link to comment Share on other sites More sharing options...
grower951 Posted March 19, 2023 Share Posted March 19, 2023 I second what @KC said, the mat should just be warm not hot to the touch it'll cook your roots and even put you at a fire risk 2 Link to comment Share on other sites More sharing options...
Axiom Posted March 19, 2023 Author Share Posted March 19, 2023 16 minutes ago, KC said: Sounds like a lot of wasted power, I think the roots like a gentle heat not a full on cook. I'd say your thermostat is fucked. I got the 200W/m2 instead of the 150W version because they are mainly used on a concrete cold floor in unheated garage during the winter... The idea was to have them working constantly to take pressure off the oil rad, as it would heat the whole tent more efficiently. There is nothing wrong with the probe / thermostat. I have confirmed this because I have 2 in different locations doing the same thing. They always have. The plants looked great throughout most of the grow and even in fabric pots, dry backs were only an issue towards the end of flowering.... and that was bottom feeding!! as for the pot in question, the plant looks great lush lime green but that could just be because I'm not overfeeding for once But still, 38c bottom of fabric pot is a bit mental and I'm starting to realise why my plants were so 'thirsty' all the time. I agree about the wasted heat too. The probe at bottom of the pots will help a lot. The weirdest part of all this is when I touched the bottom it was hot & moist My theory is that the roots at the bottom of the pot are fried and its just wet coco at the bottom couple inches of the pot. I guess I could cut it open and check and then velcro back together. 40 minutes ago, purepotstill said: I'd make a tray-sand-heat mat-sand sandwich. I'm thinking silicon is heat resistant and may act as a slow release heat buffer. If I used it as a thin layer on the underside of my trays it would protect the plastic and also dissipate excess heat to the air in the room, which means less heat cooking roots and more heating the tent. Means I would use the oil rad a lot less in the winter and at a much lower level, when it is being used. The sand idea made me think silicon... so thanks. I'm thinking there must be a lubricant / gel like substance I can apply which stays wet or drys. Either that or get some catering silicone baking sheets or something in bulk and stack them. 28 minutes ago, purepotstill said: I wouldn't want a heat mat to get so hot I couldn't touch it. You would if you were growing a giant cold stone rock. I guess I underestimated how good the Kingspan would be. Link to comment Share on other sites More sharing options...
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