Reply Tue 18 Feb, 2014 08:52 am
I am installing a wood stove this week and have a few questions as to the poured slab and heat transference. Our home is a on a poured concrete slab (no basement), our den or first level has a sub floor on top of the concrete slab, this is where we are installing the wood stove. the sub floor is 2x2" with foam, plywood then carpet. I have removed the sub floor exposing the area where I intend to build up the concrete to the same level as the sub floor, the area where I want the wood stove to be setup. My question is, should I bother to lay something down such as MDF or OSB before I pour this 50x60x3" pad? it will be against the exterior wall so I was wondering if heat transference will be an issue? should I insulate the 2 concrete slabs from one another?
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Type: Question • Score: 0 • Views: 503 • Replies: 11
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jespah
 
  2  
Reply Tue 18 Feb, 2014 09:07 am
@RushPoint,
I'm going to bump up your topic as I think it's interesting, but I don't have a response for you, except to note that your local building code might have some requirements in this area.
RushPoint
 
  1  
Reply Tue 18 Feb, 2014 09:52 am
@jespah,
thanks!

the building code only states that of the dimensions regarding the non combustible surface itself, 40x50", I added 10" to these minimum requirements so it should not be a problem.
0 Replies
 
farmerman
 
  2  
Reply Tue 18 Feb, 2014 11:30 am
@RushPoint,
if you "float" two concrete slabs against each other with some other material in between, you may invite cracks. Id pour s a monolithic slab and Id actually take some chunks out of the concrete pad so you get a better set. Remember to wet the under slab a lot before you pour.You may just want to add some perlite into the top layer to give it a different thermal signature.

Youre worried about conducting subfloor cold into the room? Does your slab sit high enough above the seasonal water table? Id be more worried about wicking if it sits within a seasonal water table But even that can be handled with a proper water proof mix of concrete

Wood stove or pellet? Pellets are great but lotsa work
RushPoint
 
  1  
Reply Tue 18 Feb, 2014 01:05 pm
@farmerman,
perlite! very interesting idea! I was thinking on using ditra between the two, I don't want them bonded as I might some day wish to remove this slab. Not so much worried about wicking, I have installed 8" socked weepers in 16" gravel depth, irrigation cloth then sod, this runs the entire perimeter of the home, ditra also runs against the slabs total perimeter with about 6" depth below the slab foundation of 10". There is a 60 foot, 10 deg. gradient that hooks up to our irrigation system that is distributed 300 feet down hill to our lower garden area. I don't expect water problems short of an artesian well spouting up directly under the foundation, lol, never know I guess!

the slab I want to pour is roughly 3 1/4" think and 2 sections, 20 sqr. feet each, 4" masonry meshing then finished with slate tile (natural cut). using SAKRETE gravel mix, I'm adding in a small amount of Portland as well as a bonding agent.

my home is 3400 sqr.', I bought a Regency F5100 95k BTU catalytic wood stove. 30 acres of matured hardwood so Wink

short of a thermal barrier between the foundation and the slab, do you think this formula will work? I was only wondering as to heat transference due to the fact my slab foundation is at grade! with -35 deg winters it does get quite cold.

thnx for your reply!
farmerman
 
  2  
Reply Tue 18 Feb, 2014 01:15 pm
@RushPoint,
I think it will work.I have a new building with a concrete floor and we get winters in the 10 to -5 F. Its such a nice thermal mass that the room on the base level is ALWAYS above freezing even with no heat, so I wouldn't worry. Sounds like you hve your water issues worked out.
. The only raso I suggested prlite would be even moe desirable if you want to eventually remove that slab and still have it act as a bit of an insulator.
0 Replies
 
farmerman
 
  1  
Reply Tue 18 Feb, 2014 01:16 pm
@RushPoint,
does your stove have a blower?
RushPoint
 
  1  
Reply Tue 18 Feb, 2014 02:11 pm
@farmerman,
blower and a top reflector, it's a rather large stove! 22" firewood with a max 30 hr. burn!!! 8hrs @ 80k BTU

I also built a duel filtered air handler separate from the HVAC system just before I dry walled 2 years ago, intake on ceiling above where I had planned to install the stove!

that "hindsight" thing is a good metaphor!

what ratio would you suggest with the perlite? or should I pour concrete on top of a layer of perlite? how would this application work?
JTT
 
  2  
Reply Tue 18 Feb, 2014 09:11 pm
@RushPoint,
Do not pour the one slab onto or into the other. Put a slip surface of some type between the two -sand, perlite, foam even visqueen or 30 pound roofing felt.

Since you want some insulation factor, foam would work best.

There is no need to even pour full depth concrete. You could fill it with rubble with a two inch cap of concrete.
0 Replies
 
farmerman
 
  2  
Reply Wed 19 Feb, 2014 05:14 am
@RushPoint,
we used to mix perlite in "light" concrete (for ornaments) at a 30 to 50% ratio (by volume) and we wouldn't ise any stone. I imagine that youd want to mess around with the mix if you keep the river stone in the mix.
Ive just come in from a night working in the barn and I slept a few hors in the new building and , without heat, it was still comfy. (Course it only went down to 15 F last night)

Is yours a "chunk" stove or a boiler unit? Im still looking for a good heating system into this 5k ft2 building on 2 floors. Its well insulated . I originally wanted a pellet stove but have found out since that pellet stoves need fairly regular and intense maintenance.

RushPoint
 
  1  
Reply Wed 19 Feb, 2014 12:11 pm
@farmerman,
with a building of your size, I would tend towards both the boiler system using a "food grade" glycol radiant floor heat for the lower level and a small wood stove on the second level. Depending on how much available wood you may have on your property of course! A boiler system doesn't so much care about the quality of wood you burn, my father built his own outdoor boiler and for over 25 years he burned literally everything from old skids to stumps, and or anything else he could drag out of the bush. Where we are, it can get as cold as -40 deg. C in Jan/Feb. (I remember one year it was -47Deg.C "with NO wind chill factor!" ) so your application may not require such a robust system!

He heated the shop (1600 sqr feet), the barn (1000 sqr feet), and his home (3000 sqr feet) all with one boiler system! They also had a small wood stove on the second level of their home and a high efficiency propane furnace for when they were away and could not attend to the fires.
He was at one time planning to augment the boiler with a propane system in the shop in effort to prevent the entire system from dropping to far in temperature when they were away, he built a 10'x10' metal addition on the shop, spray foamed the interior and had a small "botched" or reverse engineered propane furnace he planned to adapt to the glycol grid, never happened lol!

The stove I bought is one of the larger stoves on the market (520 lbs.), it will take a 22" piece of wood and the fire box is 4.5 cu ft. , so about 90lbs wood load, it has a rating of about 86% efficiency.
We owned a pellet stove years ago and I have to say, "what a huge pain in the ass!", not sure if the systems are still as bad but I'm tellin ya, I wanted to blow this stupid thing up! 3 years, then I got rid of it! they may not be as bad these days but I had everything from constant auger jams to combustion chamber malfunctions! and for what you pay for pellets you don't really get a good heat from them, not like a wood stove anyways, not much in the way of radiant heat.
RushPoint
 
  1  
Reply Wed 19 Feb, 2014 12:30 pm
@RushPoint,
outdoor boiler systems are the way to go with large homes such as yours! eventually, it's what I will have on my property.
0 Replies
 
 

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