radiant slab heat

[morpho]

Anyone have any experience with a heated slab and a wood stove and how they play together?

Basically will the slab suck in a bit of the ambient temp supplied by the stove and not kick on the boiler as much or does the wood stove just add a bit to the air temp and I shouldn't actually expect the stove to take the load off the boiler?

kind of an odd one I know...

Thanks.

 

[bholler]

if there is insulation under the slab the stove will help to heat it. But the thermostat for the furnace will not be in the slab it will be on the wall so the furnace will be on much less regardless but the slab will probably be cooler in areas far from the stove

 

[morpho]

Hi bholler

Oh she is insulated under the slab R10 and around the perimeter R10. R40 walls, R60 ceiling.
I put the thermostat in the floor actually...which works great for the boiler.
Not sure how the physics of a wood stove heat on a space though. (convection)

 

[Grisu]

The stove will heat the room air which will mean the slab will loose less heat. The boiler should go on less often.

 

[morpho]

cool...I am very interested to see what will happen this winter.

 

[DougA]

My house is built on a concrete slab, fully insulated underneath but not heated. My slab will always feel cool to the feet, even when it's room temperature, since it is a high mass. I use the slab to help regulate the temps in the home, so it will give off it's heat if the air is colder and give off cold during a hot spell in the summer. Compared to a similarly insulated wood floor, your stove will work a bit harder in the winter since it has to heat all the mass, in addition to the air and surroundings. However, since your slab is heated, I would expect it to lessen heat needed in the slab when the wood stove is on. I think you will find the heat from the wood stove much more comfortable than the heat from the slab.

 

[morpho]

sweet!
I like the heat from the slab actually, especially as I can walk around with bare feet all winter. (direct contact with the floor actually makes you feel warmer)
So I will have three heat sources. Radiant slab heated from the boiler, The slab heated from the sun (passive solar) AND the wood stove.
...exactly why did my ancestors stop here?...I have no idea. I still think they should have banked a hard left and stopped when they heard the margaritas in the blender.
Oh well.

Thanks Doug.

 

[bholler]

I agree that the stove will heat the slab some and the warm room air will reduce the heat loss of the slab greatly so furnace will run allot less. But i am wondering why you put thermostat in the slab if you are trying to heat the room with the slab heat? To me it doesn't make sense but i don't really know i am a chimney guy not an hvac guy. Can you explain the reasoning to me i really am curios.

 

[EatenByLimestone]

The temp of the slab regulates the temp of the house. You may want to use the boiler to initially heat the slab, but after that the stove, depending on type and placement, may be able to hold it. Time will tell. The hard part will be getting the slab to temp at first. After that it should be easier to keep warm.

 

[morpho]

bholler,
The stat is in the slab because it acts as a massive radiator and is slow to heat and slow to cool. So if the stat is on the wall and you reach your set point and the boiler shuts off..well that slab is possibly way past where it needs to be and it is going to keep raising the room temp even after the pump has stopped. Picture a big ole train rolling down the tracks with no brakes...if you stop feeding the fire when you get to the station, she will roll right past and keep on going. Air temp is almost irrelevant.... trust in the slab!
Works great. You avoid wild swings.

Eatenbylimestone,
Ya, there is no way the boiler will be shut off and heat maintained by the stove totally and I wouldn't expect the stove to heat up the slab enough to make a difference. I am just hoping it slows down the heat loss in the slab and thus how often the system fires up to maintain the desired floor temp...as well, the passive solar aspect is a 16' "solar south" facing triple glazed reverse energy star window that heats up the space and the floor when its sunny, but is a bit cool when it's not. I think its still a net gain overall, but when it's -40 and dark out...you can feel it pulling a bit of heat from your body a bit....thats when the stove will hopefully shine! ....that and fire is cool to play with!

When heating season starts, I fire up the boiler and it only takes a few cycles of the system as the floor really doesn't fluctuate much between heating season and summer. I raise it about 10º and that gives me a steady air temp of 72º...the air basically stays at that temp all year thanks to the concrete mass. If its really cold outside and I am losing heat, I turn it up a few degrees...but not a lot. They have fancy systems that run the boiler off the outside temp, but "I am but a simple man".

 

[DougA]

Yes, you are correct to have the thermostat in the slab for the reasons you stated. I found the slab to be poor at retaining heat from the sun in our passive solar room. We can be low 80's in the dead of winter (well below freezing outside) on a sunny day with the wood stove off but once the sun is down, the wood stove goes on fast! I've looked at an exterior wood furnace and if I had a chance to build everything all over again, it would have been wise to run it through our slab as backup. A wood furnace at this point is not a consideration since I am way too lazy to go outside to fill it at 7:00 am. on a frigid morning.

 

[morpho]

Doug,
I have no idea how much the sun adds to the system overall, but free heat is free heat as far as I am concerned. "Make heat while the sun shines" as nobody says.
I know when it's sunny, the boiler runs probably a quarter as often. Its all cumulative I hope.

I can't believe I am saying this...come on winter!..I want to make a fire in my new stove.

 

[morpho]

Ya, I looked at the outdoor wood boilers and the upfront cost was a bit steep for me, not to mention they really don't make little ones for my little hyper efficient house.
(You don't even want to get me started on the issue of finding a small enough boiler!)

To put it into perspective...It cost me about $380 of propane to heat this place for 7.5 months and it was a wickedly cold season.

 

[morpho]

Its funny, I guess my biggest concern/hope is that the wood stove helps the boiler not need to turn on as much not so much for the heat...I can turn up the heat in the floor. What I really want is for the pump to not run as much. Those things suck precious amps from the system every time they have to bring the floor up to temp. Probably would have made more sense to buy a few more solar panels to run the pump...but it's a lot nicer sitting in front of a fire...that little circulator pump is kinda ugly and boring to stare at. (though some would say so is my stove!)

 

[morpho]

 

[EatenByLimestone]

Its funny, I guess my biggest concern/hope is that the wood stove helps the boiler not need to turn on as much not so much for the heat...I can turn up the heat in the floor. What I really want is for the pump to not run as much. Those things suck precious amps from the system every time they have to bring the floor up to temp. Probably would have made more sense to buy a few more solar panels to run the pump...but it's a lot nicer sitting in front of a fire...that little circulator pump is kinda ugly and boring to stare at. (though some would say so is my stove!)

since heat will want to move toward cooler areas, keeping the air as warm as the slab should keep the slab from losing heat to the air. You'll still lose it to the ground though.

 

[morpho]

I like to think of the lost heat to the ground/foundation walls as frost heave protection.
Thats my story and what I am sticking with.

 

[Auzzie Gumtree]

Are we going for the minamalist look

 

[morpho]

Hey Auzzie Gumtree,
Looks like a cool day there in Australia...30c here today...so I am busy swinging my maul getting ready for my rapidly approaching winter.

Not so much "going for" any look in particular...just the way it turned out so far. What I find for free or cheap or local or scavenge from my scrap pile...then when I saw this stove I zeroed in on it.
I like it a lot, but I can appreciate it's not for everyone. Though I can say I probably do lean towards more open space and less doodads all over the place...so maybe that makes me a minimalist I guess.
Hill Billy Minimalism... I like it....wonder if I can trademark that?

 

[Auzzie Gumtree]

doodads

Never mind trademarking Hill Billy you should try "DooDads" not heard that one before is it a Canadian-ism.

Where abouts in Canada are you from? i've been a couple of times but always in Summer. The winter here is pretty mild for most of you guys but it gets close to freezing most nights and up-to 5 -10 in the day. Still feels cold when your house has a lot in common with a sieve.

 

[Beauly]

I am interested in this thread... Just moving into a new, (to us) house, which has radiant heat in an insulated slab in the basement, and radiant tubes stapled under the first floor between the joists, with insulation under the tubes and maple flooring above on the floor. This will be our first winter. Yes I am not optimistic about the first floor stapled under the sub floor radiant tubes. Maple is nice, but not much thermal mass to play with!

However.....

Out goes the gas fireplace on the first floor in the living room with the cathedral ceiling leading to the two bedrooms upstairs...

And in comes the Scan Anderson 10 wood stove. (With the soap stone kit) ta dah!


So what is going to happen?


In floor heat will have very flat curve, right?

Woodstove, lit each night when we come home for the evening... I'm thinking it will add a nice boost of warmth into the living, kitchen and dining areas each night that the radiant just can't do....

Thoughts?

 

[morpho]

Never mind trademarking Hill Billy you should try "DooDads" not heard that one before is it a Canadian-ism.

Where abouts in Canada are you from? i've been a couple of times but always in Summer. The winter here is pretty mild for most of you guys but it gets close to freezing most nights and up-to 5 -10 in the day. Still feels cold when your house has a lot in common with a sieve.

I am...hmmm?...in the middle of the sticks in the province of Alberta if you have ever heard of that place.
Ha! your winter highs are my summer lows...sometimes I hate this place.

I lived overseas with a bunch of Australians over the years. (You folks are nuts by the way...just in case you were unaware of this fact...I am still mentally scarred by the events. Lets just say it involved A LOT of VB)

Doodad?...I don't know if it's a Canuckistan thing or not...just something my Grandfather used to say. Doodads, doomahickies, whatchamacalits...

 

[morpho]

I am interested in this thread... Just moving into a new, (to us) house, which has radiant heat in an insulated slab in the basement, and radiant tubes stapled under the first floor between the joists, with insulation under the tubes and maple flooring above on the floor. This will be our first winter. Yes I am not optimistic about the first floor stapled under the sub floor radiant tubes. Maple is nice, but not much thermal mass to play with!

Hey Beauly,
I have exactly zero experience with staple up radiant.

The slab in the basement will...ok..."should" send heat up to your living space in a steady rate. Is there an air circ fan from the basement to the upstairs?
The staple up will add to the whole thing and feel great on the feet for sure, but I don't have a clue how it maintains any kind of flywheel effect if at all. But thats where the slab comes into play..???
I think you will be surprised at how well it works.

Now, how to fit in your new stove into the heating scheme is another thing altogether. You might find you can turn down the staple up if the wood stove is running...(or shut it down altogether...but your thermostat will probably do that for you)
Cool stove by the way!

Anyway to contact the previous owner? They probably had it dialled.

 

[Highbeam]

I have a radiant heated slab in my shop as well as a woodstove. I haven't gotten the floor heat running yet but I plan to use the two seperate heating systems independently as stages. The floor heat will get me up to 40-45 and the woodstove from 45 on up. I put in a sleeve for a slab thermostat.

I can't imagine the two heating systems not fighting each other. I think you'll find yourself overheated since the slab that is set for say 70, will still be making the btus necessary for 70 but then the woodstove will pump in more btu. The fix is to set up your floor as the low stage. The floor gets you to 60 and the stove to 80.

You are further crippled by the differences in thermal storage. The slab takes forever to respond but the stove is kicking out heat right away.

I would expect some hot times and cold times while you try and prevent waste.

 

[morpho]

Hello Highbeam
Hmmm?
Well....aren't you just the downer on my little party!

What do you mean by "prevent waste"?

So if I turn down the set point on the slab and bring the space temp up to "cozy setting" with the wood stove, do you figure it will meet in the middle somewhere? (literally and figuratively... as in find a happy heat and that the slab will soak in some of the ambient room temp into the top inch or so)

Could be wishful thinking...I have zero understanding of physics.

Either way I guess I will find out soon enough!