Thread: Insulation for heated pond

Hi Andy,
my view is that over time the kingspan would give way under the massive weight of the water - so I'd recommend not insulating the base. I just insulated the sides of my part raised pond and I've found it quite good at retaining the heat over winter. Also by insulating the floor you miss out on any ground heat coming up through the base.


IMG_3304.jpg

a bare pond floor will act as a heatsink helping to stabilise temperature swings.
especially in winter, if you insulate the walls well, to the equivalent of 100mm of celotex (4.50m2K/W), and 35mm polycarb on top.
mine hasn't dropped below 12C all winter with no heating.

Originally Posted by ABN67

Thankyou davethefish1
Joining this forum was one of the best decisions I made when I decided to build a koi pond, there's so much to learn from the wealth of experience here.

I'd agree with that.

I found the info and advice on here so helpful.

I definitely avoided making a number of wrong decisions thanks to this forum.

Sent from my Pixel 4a (5G) using Tapatalk

Just an alternate view…This isn’t always the case. For me the floor should be insulated. For example if heat warms the floor, why insulate a house extension floor?
Alot depends on your ground, on poor ground (ie heavy clay with groundwater) surely that isn’t going to warm the pond with ice cold water under the slab unless I’m missing something? Also for example on my pond I insulted to give a good dry base for the fibreglass as the slab never fully dried out. I’ll never buy into the collapsing insulation either! Fibreglass is extremely flexible

it only gives heat up at a given depth down, ground temperatures are warmer at depth and generally never freeze...but only usually single digits unless you have heated it all summer
a house is ground level or above so wouldn't benefit, especially as a house is generally 20C+ a lot warmer than underground temperatures too.

there's swings and roundabouts to both methods i think.
if you don't insulate the floor it takes more energy to heat it in summer, but it gives heat up if not heating high in winter...

if you insulate all areas in cluding the floor it will hold heat better if heating above ambient, but has no thermal mass other than the water its self... so if you stop heating, it will lose heat more quickly.
depends on what you want to do...

This is something I came across when installing water pipe.

Says it all really and essentially supports the non-insulated base argument:

According to 'The Department for Environment';
"Pipes should be buried at least 600mm (two feet) underground. At this depth, the soil acts as a natural insulator and prevents them freezing".

However I believe the current recommendation is actually now 750mm.

Originally Posted by RS2OOO

This is something I came across when installing water pipe.

Says it all really and essentially supports the non-insulated base argument:

According to 'The Department for Environment';
"Pipes should be buried at least 600mm (two feet) underground. At this depth, the soil acts as a natural insulator and prevents them freezing".

However I believe the current recommendation is actually now 750mm.

agreed, it's the basis of ground source heat pumps.
they are more efficient that air source heat pumps.
but you need more land to make it work well and it costs a lot more to install

just concept art...not a bad size house though but garage way too small lol,

Originally Posted by deejaysmi

It's like that old question - what does more damage to a wooden dance floor, an elephant or someone in stiletto heels?
Yes there is a large weight of water but it is spread over a huge area; the hydrostatic pressure at 2m deep is about 0.2 Bar.
Also think about diving to the bottom at the deep end in your local swimming pool, your ears will pop but you're not going to be crushed....

at the sides of the pond that is true,
as gravitational forces are perpendicular, so only the water pressure at 0.2 bar (20 kPa) at 2 meters deep is pushing against the side walls.

but what the insulation under the floor is actually supporting the gravitational weight of the water at 1000 kgs/m2/ meter deep, spread across the floor area.
so at 2 meters deep is supporting a load of 2,000kg per square meter of compressive force.

thats a lot, and standard celotex/kingspan PIR type roof insulation K107 is only rated to a compressive strength of 100 kPa or 1,000 kg/m2 at 10% compression.

a standard flooring specific insulation like TF70 has a strength of 140kPa or 1,400kg/m2 at 10% compression.

but some high strength flooring specific insulation like kingspan GG700 is rated to 700 kPA or 7,000 kg/m2 so will compress much less at 2,000kg/m2

or kingspan GG300 at 300 kPa or 3,000kg/m2

https://www.kingspan.com/gb/en/produ...oof-board/?s=t

https://www.kingspan.com/gb/en/produ...loor-tf70/?s=t

https://www.kingspan.com/gb/en/produ...ard-gg700/?s=t

this is Scorchios pond who had some leaks due to compression of the insulation debonding some of the connections on the side walls and bottom drains.
looks to have been a double 25mm layer of standard PIR insulation that would probably compress more than 20% so over 10mm compression.

the fix was the company removed the floor and insulation and re glassed the pond.
would have helped to dish the insulation to the bottom drain and seal against the flange...


https://www.koiforum.uk/pond-constru...d-build-7.html

If you layed the Fibreglass up properly then insulating the floor would be fine, but we're talking a lot more layers then the normal pond 2 layers 450csm and some tissue. This is because that is a tiny amount of fibreglass and just enough to waterproof a structure (some pros only do one layer 600csm and tissue because they're good enough to get away with it). Going over insulation at the floor you'd need to account for the compression by making the structure out of something else, but its still not ideal.
You'll need to consider that you'll loose the heat sync with the ground which, arguably, you want to have if you aren't heated, but probably want to avoid if you are heated.
So basically don't bother, unless you're heated. If you're heated, I'd make a steel box section frame to make the structure (or bricks)and insulate the gaps, possibly marine ply over the top or similar then do a heavy lay up with the Fibreglass. This way the Fibreglass will only want to compress in between the frame sections.

... guess work here, but if you did the frame sections say 450mm wide across the longest side of the pond and, depending on the width, had a support down the middle or every 900mm or whatever looks right, then that would be ideal.
Either that or find some poly foam insulation that won't
compress. Fibreglass suppliers sell a high density poly board about 8 or 10mm up to 100mm but the thick stuff is about £150 for 1200mm length.