Q: Protecting pots + trays from underfloor heat mats

[purepotstill]

I grow in a cold garage too. Temps can get as low as 5°C in the room (but only in the heart of winter, not now). Best thing I've done to make the oil rad more efficient is to build a box around it where's the intake is and insulate the tent with thin insulation material. Looks like that. The non insulated wall you see overlooks the house, so it doesn't need it.

 

[Axiom]

@purepotstill When are you launching the shuttle?
That looks good, what are you using to hold the insulation together? velcro?
I've done the bottom of mine but not done the sides yet. I've got a roll of bubble insulation ready to go just not had the time yet. 
Hoping it keeps tent cooler in the summer also.

 

I need to build an oil rad box that's going on the to-do list!

[Wacky Wardrobe]

2 hours ago, Axiom said:

Can you link it for me or let me know the product name and where to find it please?

Ebay £8 : Fan Speed Controller Fully Adjustable Lighting Lamp Dimmer Switch MAX 300w

 

You'll be able to reduce your wattage with this and run the cable at a lower temperature.

You can aim to have it stay on all or most of the time instead of cycling with a little trial and error.

[RUFUS HOUND]

alright mate, just so i understanding your set up.

 

You have 200w heat matting, I presume this is the under floor variety and not a seedling heat mat.

These types UFH are normally fitted buried under tiles and adhesive, which gives it mass to store and help dissipate the heat.

what size is your tent and heat mat ?

 

I run with a 90W garden heating cable buried in a sand bed linked with a temp controller (for root temps only ).

The probe from the temp controlleris close to the middle of the pot and buried all the way down, to about an inch from the base of the pot set at 24'C.

 

I would say you need more thermal mass, try your mat under a few floor tiles with your pots on this and see if it helps

Edited March 19, 2023 by RUFUS HOUND

[purepotstill]

1 hour ago, Axiom said:

That looks good, what are you using to hold the insulation together? velcro?

Yes, dual lock velcro.

[iShouldCoCo]

3 hours ago, Axiom said:

I'm thinking making a hole right at the bottom and setting the temp to about 22 might solve the issue.

I did this, although my big square pots have large holes that open to the bottom and side so perfect for probe poking.. no issues so far!

[Axiom]

36 minutes ago, RUFUS HOUND said:

You have 200w heat matting, I presume this is the under floor variety and not a seedling heat mat.

Yep, bang on. 

36 minutes ago, RUFUS HOUND said:

what size is your tent and heat mat ?

1.2m tent but for that space iv'e used 1m2 of adhesive backed wire the underfloor type. 

1.2m2 was out of stock for the 200w version I wanted.
The wires are quite thick.  

36 minutes ago, RUFUS HOUND said:

I run with a 90W garden heating cable buried in a sand bed linked with a temp controller (for root temps only ).

The probe from the temp controlleris close to the middle of the pot and buried all the way down, to about an inch from the base of the pot set at 24'C.

 

I would say you need more thermal mass, try your mat under a few floor tiles with your pots on this and see if it helps

24 is nice but remember when the heat switches off from the mains the wires stay hot for a bit, and that can climb quickly in the summer. 
For this reason I tend to set my thermostats 1-2 degrees below target.

1 hour ago, Wacky Wardrobe said:

Ebay £8 : Fan Speed Controller Fully Adjustable Lighting Lamp Dimmer Switch MAX 300w

 

You'll be able to reduce your wattage with this and run the cable at a lower temperature.

You can aim to have it stay on all or most of the time instead of cycling with a little trial and error.

This has got to be the winner! As long as it doesn't burn the house down? This thing works with heating elements? Seems designed for fans so can someone tag an electrician pls  

Just now, purepotstill said:

Yes, dual lock velcro.

thanks bud.

Just now, iShouldCoCo said:

I did this, although my big square pots have large holes that open to the bottom and side so perfect for probe poking.. no issues so far!

no harm in poking a hole in fabric either  ... I actually cut my pots open when I'm done with a Stanley knife and then staple them or use safety pins for the next run.
Works a treat if you need to look at your roots too  

[Wacky Wardrobe]

24 minutes ago, Axiom said:

This thing works with heating elements?

As I said. I use them myself at times specifically for this purpose.

It's a simple dimmer. Works for light bulbs, heating elements, fan and pump motors etc.

I have heat mats with a similar device built into the cables.

As long as you observe the max wattage rating it will be fine.

 

[ratdog]

get some ceramic/porcelain tiles to sit the pots on, i do and works a treat

[RUFUS HOUND]

41 minutes ago, ratdog said:

get some ceramic/porcelain tiles to sit the pots on, i do and works a treat

already said that in my post but he seems to have skipped over that

[Clubs]

There's another way to do it, which I found quite effective. 

 

So, without trying to sound more scientific than I'm capable of, hold your hand over a heat mat and you'll detect no warm air, therefore,  for heat to transmit from the mat to the inside of the pot, there needs to be direct contact between the two. Unfortunately, this almost always results in a hot surface where your roots reach and rest across the bottom of the pot, damaging the roots in the bottom and stressing the plant. This is why I often use a layer of capillary mat - to soften the impact of direct contact with a heating element. 

 

However, when you press a plate onto the mat, one with high thermal conductivity properties, such as an aluminium plate, this heat then warms the air space above it. Pizza trays are ideal for this and you can get one in your local supermarket for around £6. 

As you have now heated the air under the pots, you can use a little mesh/criss-cross construction and sit your pots on top of that. If using a plastic Airpot, their bases are raised off the ground anyway so they can go straight onto the pizza tray.

 

If you're concerned about water pouring over the mat, you can put one those thin aluminium disposable baking trays on top the mat. The weight of the pot keeps it all down flat with a warm cushion of air under the pot.

[RUFUS HOUND]

3 hours ago, Wacky Wardrobe said:

Ebay £8 : Fan Speed Controller Fully Adjustable Lighting Lamp Dimmer Switch MAX 300w

 

You'll be able to reduce your wattage with this and run the cable at a lower temperature.

You can aim to have it stay on all or most of the time instead of cycling with a little trial and error.

top tip mate , I have one of those on my exhaust fan - never realised it could give me basic control over heat mats

[Baron von greenback]

My mate uses a dimmer switch for your house lights he just cut the cable and wired it in from both sides I think any kind of kit that dims anything can be used to control other things also on the heat mat issue I got some ot them like sponge big jigsaw thing you get for kids to do on the floor they hold the heat in quite well and there cheap but like I think Rufus hound said you have proper underfloor heating should screet on top then tile adhesive then your tiles absorbing all the heat 

[Michael Luchóg]

The sand and the element are the right shot, still used in commercial nurseries . I guess a small underfloor heat mat with a bed of sand would be ideal as the temperatures can go up in 2 degrees C or something like that. The display shows increments of 0.5 degrees but the click comes every few degrees. That's Chinese stuff though, eh! The sand is a great conductor, maybe not the handiest for an indoor set up. Never tried it except with a layer of sand in a heated propagator, rooting cuts on a cold window.

[Devon Cream]

Had same problem started using the RTA system pot trays.