Insulating under WFO

[ErnieH1]

Hi there

Firstly, as this is my first post - Hi all.

I’ve got a really quick question. I’ve purchased a readymade woodfired oven (sorry to everyone who will frown on this). It is handmade, I’ve gone for their best insulated model. I’m time short and struggling to get materials at the moment due to Covid shutdowns so it was the easiest way for me to get on with finishing one part of the garden.

I’m building the base for it to sit on. The guy who I’m buying it from just said to build two piers and he always puts a 25mm ceramic board underneath and drops the oven on. I’m building a square with some lintels across part the way up to leave a wood store at the front and I was thinking about adding some thermal mass in the void under the oven.

I’ve been reading this forum for a while and people always say they’d add more insulation to the base. My question is this, would a 50mm/2” of ceramic fibre board be sufficient or will I see benefit if I fill the void under that with a vermiculite/cement mix? Alternatively, would it be worth filling with glass bottles or alternatively would I be better concreting to provide extra thermal mass under the fibre board?

I hope this makes sense, I want to make sure the base is well insulated. The spec of the oven seems to suggest the whole oven including floor is well insulated but obviously I’d need the ceramic board as a minimum to prevent thermal bridging into the blocks below.

Any advice greatly appreciated as I’ve already concreted the pad and will start building the walls in a day or two so could do with figuring out what’s best to order, fibre board, vermiculite or both.

cheers for reading.

[UtahBeehiver]

https://community.fornobravo.com/for...nsulation-base

[ErnieH1]

https://community.fornobravo.com/for...nsulation-base

Thanks for this. Sounds like calsil will be easier. Only other question would be, is it worth me filling the void under the over and calsil with anything and would I go for further insulation (loose vermiculite or even glass bottles) or would I be better filling it with mass such as concrete fill up?

Thanks in advance.

[david s]

My view is that it is the ideal place for wood storage as it’s warm. Also if air is able to flow through it’s better as a U shape restricts this and can result in a damp space.

[NCMan]

Thanks for this. Sounds like calsil will be easier. Only other question would be, is it worth me filling the void under the over and calsil with anything and would I go for further insulation (loose vermiculite or even glass bottles) or would I be better filling it with mass such as concrete fill up?

Thanks in advance.

If I understand you right, adding any thermal mass under your insulation will do no good, since you've already provided insulation. Thermal mass will have hardly any advantage if done like that. You'd want any and all thermal mass adjoining the oven to actually do any good. Also keep in mind that thermal mass can require more fuel/time to heat your oven.

[ErnieH1]

My view is that it is the ideal place for wood storage as it’s warm. Also if air is able to flow through it’s better as a U shape restricts this and can result in a damp space.

Thanks for the help. I was creating an area for wood storage underneath but was going to put a few lintels across part the way up so I could get more fill under the oven. I was thinking that the wood under here would just be decorative as in the UK climate it’ll be constantly rained at, especially when we get driving rain.

Thanks again.

[ErnieH1]

If I understand you right, adding any thermal mass under your insulation will do no good, since you've already provided insulation. Thermal mass will have hardly any advantage if done like that. You'd want any and all thermal mass adjoining the oven to actually do any good. Also keep in mind that thermal mass can require more fuel/time to heat your oven.

Thanks for this. Would you think it worth adding extra insulation to the void under the calsil like bottles or vermiculite or would 50mm/2” calsil board be sufficient? I am wondering if the 50mm calsil on top of the side walls and on the other side touching the underneath of the oven would create a thermal connection so any fill in the centre would be negated by this and rendered pointless.

Is just 50mm calsil going to be plenty? The oven base is already insulated, I can check how exactly but I know the base is supposed to be well insulated when it arrives. I just want to be without regret on the platform insulation.

Thanks for taking the time to help, much appreciated. My oven arrives Monday and I’m building the walls tomorrow. Just need to find someone who can lift it over the wall for me now and maybe an engine hoist to get it up on the platform.

one other quick question if no one minds. The guy making the ovens said he sticks the calsil to the block piers with heat proof silicone. Given the weight of the oven, is this necessary as it’s hardly going to be moving once the weight of the oven is on it.

[NCMan]

Thanks for this. Would you think it worth adding extra insulation to the void under the calsil like bottles or vermiculite or would 50mm/2” calsil board be sufficient? I am wondering if the 50mm calsil on top of the side walls and on the other side touching the underneath of the oven would create a thermal connection so any fill in the centre would be negated by this and rendered pointless.

Is just 50mm calsil going to be plenty? The oven base is already insulated, I can check how exactly but I know the base is supposed to be well insulated when it arrives. I just want to be without regret on the platform insulation.

Thanks for taking the time to help, much appreciated. My oven arrives Monday and I’m building the walls tomorrow. Just need to find someone who can lift it over the wall for me now and maybe an engine hoist to get it up on the platform.

one other quick question if no one minds. The guy making the ovens said he sticks the calsil to the block piers with heat proof silicone. Given the weight of the oven, is this necessary as it’s hardly going to be moving once the weight of the oven is on it.

The short answer is that any and all insulation under and around your oven is a good thing. Always. As for the quality of bottles, etc., that is left to you. I would do whatever you can, as it's the only chance you get, especially pertaining to the underside. Yes, pay attention to potential thermal bridging, which can and will soak up heat. The calsil will be ok, but more is better. As for the calsil being attached via silicone, that may not be necessary, but might help when the oven is being moved into place, to keep it from shifting. But, if you aren't concerned w/that, it is not needed. I personally would use it to avoid that possibility, since the oven is heavy and may need to be shifted a few times to get it in place and it may move your calsil (?) Best of luck to you and keep us all posted.

[ErnieH1]

The short answer is that any and all insulation under and around your oven is a good thing. Always. As for the quality of bottles, etc., that is left to you. I would do whatever you can, as it's the only chance you get, especially pertaining to the underside. Yes, pay attention to potential thermal bridging, which can and will soak up heat. The calsil will be ok, but more is better. As for the calsil being attached via silicone, that may not be necessary, but might help when the oven is being moved into place, to keep it from shifting. But, if you aren't concerned w/that, it is not needed. I personally would use it to avoid that possibility, since the oven is heavy and may need to be shifted a few times to get it in place and it may move your calsil (?) Best of luck to you and keep us all posted.

Thanks for this. I’ll let you know how I get on. Cheers.