We are well underway with a new ICF home 2200 sq ft – walk out basement. Our method of heating will be an outdoor gasification wood burning furnace with radiant heating throughout the house. Our initial intention was infloor in the concrete as well as under the floorboards upstairs. Our builder insists that putting the lines in the concrete floor of the basement is not a good idea. That an incredible amount of heat is lost into the earth below the concrete (even with insulation) and that there are nightmare stories out there about people having problems with the lines under the concrete and having to break up there floor. Can anyone either support his concerns or put them to rest? It is the first and only house we intend on building, so the plan is to get it right and the way we want it from the beginning! This topic is a bit of a stressor right now as the only people we have to ask around here are the ones who sell the product and are unlikely to tell you don’t do it.
Also – is just running the lines under the floorboards with heat transfer plates an efficient enough method of heating the upstairs?
Thanks to anyone with some advise!
Replies
With over 20 yrs of inslab hydronic......
I'd say it will work well.
As with most anything, if it fails you lose. Done right, how long will it last? Don't know-only 22 yrs experience in it so far.
Layout walls you plan on putting in the basement-don't put hose there.
Take pictures with some sort of scale in the shot so you know where the hose lies later in life.
Sleeve even flexible tubing where it passes through block, cold joints etc in the slab.
All connections are above slab and don't run more than a couple hundred feet of hose w/o returning to the manifold and begining again.
Layout closer at exterior walls, don't put under cabinets or too near a toilet flange (they say it will melt the wax-I haven't found that to be a problem and within a few inches of the flange-remarkably it warms the seat................)
Best of luck.
Some thoughts
I have no idea how much of an issue it is to bury the heat loop in a way that makes it inaccessible should it need repair. I think it would prudent to avoid it though. In the situation described in the first post, I would look for a way to install it in the ground floor / basement ceiling only.
From that location, I would want the heat to conduct upward to the first floor from where it could radiate upward, and radiate downward into the basement. The downward radiation would heat all the objects in the basement, including the concrete floor. Then all of those objects would conductively heat the air, which would then circulate by convection and heat the walls. In terms of pure radiant transfer, the basement ceiling would be more effective than the first floor because the basement ceiling will have more unimpeded surface area.
I would make this hydronic loop accessible from the basement, as opposed to burying it in the subfloor. For the downward radiation, an ideal radiant surface should be provided. It would probably best to use two loops, each as a separate zone. One loop would conduct upward, and the other would radiate downward.
I am not conviced that, if you were to bury a loop in the basement floor slab, it would be a heat loss problem. Although, I do not know how much insulation would be needed under the slab to avoid excessive loss. But you would have a large temerature difference between the slab and the ground. I would heavily insulate the basement walls and slab, even with the heat in the ceiling.
In slab is a proven system:
The in slab hydronic heat is a well proven system. But it does need to be designed for the climate to work well.
I have seen problem systems, the worst constructe by my ex brother in law, aka Concrete Boy.
Concret Boy and his buddy the plumber designed and installed a pex tube system that was atrocious. There wasn't any insulation under the slab. Concrete Boy decided that he would thicken the slab, and put the tubes in the top, because heat flows up (it doesn't unless you talking convection). He tied the tubing to #3 rebar with out enough chairs or supports under the bar, so when they placed the concrete they pushed the bar and tubing into the bottom of his thick slab. They did manage to pull it back up in a few places, but not most.
They used a propane water heater for the heat source instead of a dedicated boiler. The water heater could deliver about half the BTU required for the 4500-sf home, if the place had been built as a well thought out and insulated stud framed structure with r-30 walls and an r40 roof. This place, however was a log home that he had been told not to chink, until the logs settled under their own weight and closed the gaps. Maybe in British Columbia, where the company he bought his log home package from is located, logs will stay moist enough to settle. In the mountains of southern Idaho, the logs never moved. YOu could see daylight through every extrior wall. Concrete Boy, was burning thorugh two or three 500-gallon propane tanks a month, in a not too cold winter.
Concrete Boy is firmly convinced that hydronic heat doesn't work.
I completed a 5200-sf office building this year. The floor is a concrete slab on grade. There is 8-inches of foam, over a moisture barrier, with a vapor barrier over that. The pex tubing is tied to #4 rebar at 12-inches on center, at midslab of the 6-inch slab, the foundation walls all have 4-inches of foam, to 8-ft below grade. The exterior walls, are framed with 2X6s and filled with blown in fiberglass in the interior. There is 4-inches of foam on the outside of the house wrapped sheathing. The ceiling has 14-inches of blown in fiberglass.
We used the hydronic system to heat the building once we were dried in last winter. The system was on 24-7, for four cold months at 68-degrees. It took 165 gallons to top of the tank last spring.
I'm convinced hydronic works.
It is like most things: well designed systems, properly executed work well; and poorly designed systems, poorly executed work poorly.
I strongly encourage you to find a mechanical engineer, and/or heating contractor who have built enough systems to know what they are doing. Don't leave this to the general, who doesn't think hydronic works. His system probably won't.
WenWS,
You mentioned in the top post that you would be using an outdoor gasification wood buring furnace. I am curious about that furnace. Can you tell us a little about it, how it works, and who makes it? Thanks.
Slab heat
I did the slab our home in Calgary and insulated underneath with a styrofoam product called Insulworks from Beaver Plastics that has built in slots which your pex will clip into. One does need a quantity of jagged plastic staples to help the secure the pex tubing on corners and runs out of the raceways.I find it worked beautifully and have zero regrets. I am also a 23 year professional plumber. My floor section started with the gravel, followed by vapor barrier, the insulworks with the pe installed and then I put the rebar over that whole arrangement. While my foundation was not ICF, I did insulate all the basement foundation walls with 1 1/2 sheet foam; and utilized it to hold down the corners of the slab insulation so that no sheets were uplifted during the slab pour. It also prevents thermal bridging from the heated slab to the walls so it worked well for me. I would recommend that you run another piece of 3/4" pex tubing to a spot in your slab that is equally distant from a few separate loops, plug that end and bring it out of the slab alongside your heating loops; this is to function as a slab sensor conduit. You can better control the heat with a slab sensor.
I heated our upstairs floors as well, but didn't use the heat distribution plates. I wanted to use real sand-on-site hardwood flooring and was concerned with fasteners getting through. I devised a system where I cut plywood into 2 1/2" strips and fastened them to the bottom of the top web of my engineered I-joists; I then clipped my Pex to the bottom of these strips which gave me about 2 1/4" stand off from the floor sheathing. Underneath this I fastened a double layer foil bubble wrap and then had all the joist cavities sprayed with 1/2 lb spray foam as I already had the contractors doing the house exterior walls and attic with 2lb spray foam. In the instances where the HVAC return air ran in a joist cavity, I installed the tubing and bubble wrap as noted, but followed with a layer of 1" fibreglas foil face insulation and then fabricated a metal liner out of return air joist liner where I used a hand seamer to fold the edges to allow screws to tighten the liner in tension against the joists. This prevented the negative pressure of the return air from collapsing the assembly and restricting proper airflow. A second failsafe for the fastener concern is that I installed a double 5/8" subfloor, so as it turns out the 2" hardwood cleats don't even penetrate that at all. This sytem works very well and operates fantastically at a lower water temperature than normally called for in a staple-up installation. My only regret is that on start up it does have a few expansion noises here and there that I was quite careful to avoid, but its quite minor and frankly imperceptable with a bustling household, just when its quiet at the very beginning of a heat call do you notice it. Once the system is warmed up its dead silent.
I'd like to install an outdoor wood boiler eventually as a secondary heat source, as much for novelty as redundancy, but am very happy with the choice of boiler I made; an IBC 15-150. The only thing I would change there is the wall I mounted it on. I think its best mounted to a wall fastened to the foundation wall, but left away from the rest of the framing. It operates nearly dead silent, but on initial firing it makes an abrupt click when the gas valve snaps open 100% before modulating down to its chosen rate of fire. Again just something perceptible when its quiet, but mine is right under my headboard and adjacent to a bedroom wall. I sheeted my mechanical system wall entirely in 3/4 good one side plywood and painted it prior to installing anything, and its a great way to make it tidy.
The attached photo of my mechanical room is a bit old, before I had a few things completed or the floor epoxied, but the meat and potatoes of the heating system is there. The boiler serves the basement slab and main floor "staple-up", an HVAC fan-coil, and a stainless steel domestic hot water heat-exchanger style tank.
Radiant slab
I am almost finished with a similar type house - 2100 sf, ICF , slab-on-grade, all radiant heat, Tarm Solo Innova gassification wood boiler.
I have also heard some of the radiant heat horror stories, and all of them (that I have heard of at least) are caused by poor installation. Concrete will contract as it sets up, that's why you put in expansion joints. You should avoid having pex lines cross these joint as much as possible. If you cannot avoid them, you should put the lines in a sleeve across the joint. The sleeves can be black PE tubing or there are special sleeves sold for this purpose. I have pictures of my installation if you are interested.
As far as heat loss in the slab goes, I have 2" of foam board, as well as the foam from the ICF at the perimeter. That is the minimum I would go with. I had to insist on getting this much in, my contractor said it was a waste of money. Don't rely on the radiant barrier stuff - it's a scam.
In Denmark - where I come from - they use 13" of styrofoam under the slab by code! This is probably a bit excessive.
So, all in all, a radiant slab is a good way to go if it is done properly.
Thank you to everyone who provided input! I was very pleased to find a site that I could reach a broad audience to get input! I am guessing by this weekend a decision will be made as to whether the pex lines are going in the concrete or not! Seems most think it is best!
To answer some questions
Location - Easter Ontario - about 2 hrs west of Ottawa
Outdoor Furnace - Central Boiler E Classic (CentralBoiler.com)
When everyone speaks of slab on grade - we dug a big hole for our "walk out" basement and had to break a lot of rock - the building inspector wasn't happy with the idea of step footings in this "fractured rock" type location, so we have now filled and compacted a huge amount of Quarry ran, minus 3 rock - and had it compaction tested by an engineer. So there is anywhere from 2 to 6 ft of this stuff under our foundation. That said - we were told we don't need a frost wall given what we have in the hole!!! We will be back filling up to the home to bury some of the basement and attempt a ground level walkin main floor! - not sure if this is slab on grade or not!
Thanks again for your help!
Wendy
In-floor Heating
I am designing a house in northeast Alabama to use radiant heat flooring. It looks like all the comments in this thread are from those who have built houses way farther north than we are. What kind of insulation should we consider? Walk-out basement will have heat under slab. First floor will have heat under engineered joists. Our coldest winter has temps only in the single digits to teens F. CaberTosser, that was an excellent description of the method you used for your under joist installation. I wonder if that method is way overkill for the climate in our area. Would you possibly have any pictures of the under joist installation?
For in-floor heating above a "conditioned" space insulation under the heating elements is irrelevant to overall efficiency, and only affects how much of the heat is directed upwards.
One Idea:
I am designing a superinsulated house that will be one story with a full basement. The basement will be high quality space with concrete slab floor. I will heat the house with a hot water boiler and a distribution loop on the basement ceiling. The loop will run around the basement a few feet in from the perimeter, and maybe make another pass down the center. But there will be no comprehensive grid as is typically used with in-floor hot water heating.
This heat loop will be fin tube radiation elements, which heat by conducting to air and causing convection currents. This will heat the air under the basement ceiling, causing it to spread out and evenly conduct heat to the whole ceiling. The warm ceiling will then radiate heat straight down to heat the slab. It will also heat all of the contents of the basement with radiant transfer.
The warm ceiling will conduct heat upward to the first floor, which will heat air, causing it to rise, and will also heat feet by conduction, and heat all the contents of the first floor by radiation. The rising warm air plus the upward radiation will heat the first floor ceiling, which will re-radiate heat downward to the contents of the first floor.
What this lacks is the ability to put the basement on its own zone. But with high insulation values, I don’t think there is a need to maintain the basement cooler by having its own zone. There is the possibility of having multiple zones in the basement ceiling loop by which each zone would affect part of the basement and the corresponding part of the first floor. However, I anticipate using just one zone for the whole house.
KD
You say you can heat the slab with a couple loops around the perimeter, down the middle and radiant fin tube on the ceiling of the basement?
How did you come up with this idea?
Currently we are heating the house with a masonry heater. The floor is a slab with hydronic. The rooms are warm, the slab is cool.
Just to clarify, there is no heat piping in the basement slab. The perimeter loop I am referring to is fin tube, and it is all on the basement ceiling. It is not buried in the floor system of the ground floor. That is the system I used on the house I am in now, and I would use it for the next house, if I build it.
This house is two stories and a full basement. All three levels are 680 S.F. each. Here I have baseboad fin tube on the upper level, but not on the ground floor. To get the heat to the ground floor, I put the hydronic loop on the basement ceiling to spread the heat out on the ceiling and conduct through to the ground floor. I also have an open stairs into the basement, so warm air can rise up directly into the ground floor level.
I have two zones, one for the basement loop and one for the second story loop.
I have really high insulation values, so the heat load is light. So with this much insulation, I can just pour the heat in anywhere and it spreads out evenly throughout the house.
The house I am designing now will be one story, so it will just have one heat loop on the basement ceiling. The only thing that I need to work on some more is the exact design of the basement ceiling and the mounting of the heat loop. Depending on how that is detailed, I can direct more or less radiation downward into the basement. Non-gloss finishes are the best radiator surfaces. Such a surface could be above the heat tubes, or below them, so it hides them.
So as the fin tubes heat the air at the basement ceiling, the air spreads out and uniformly heats the entire ceiling. Then that whole ceiling becomes a radiator to send radiant heat downward. That downward radiation heats the slab, so it is not uncomfortable to walk on barefoot. And the heat also conducts upward to warm the ground floor.
ok
So right now you have one in operation that heats the basement ceiling and then somehow the slab is warm to the toes.
Find it odd, as even with isolating the slab from the ground and surrounding foundation, most will find the slab "cold".
A radiant cold.
I have not paid too much attention to the basement slab. It will receive radiant heat transfer from the basement ceiling, but my main concern was getting the heat to come through up to the ground floor from the basement ceiling loop.
That loop also heats the basement by heating the air from the top down. But generally, the basement feels fairly uniform in its temperature, and the basement floor is not objectionably cold to bare feet. But actually, I should check that slab temperature this winter just to see what it is. I could optimize the materials and finishes on the basement ceiling to radiate more heat down to the slab. I could also reduce the amount of air that gets heated in the basement. The main point of heating air with the fin tube is to create a shallow layer of warm air that spreads the heat out to the ceiling and thus to the ground floor.
This is a two-stage remodel that was almost a teardown. The only thing left of the original house is the basement. And there is no insulation under the slab. But when I bought the place, I dug up the foundation down to the footing and put 4” of extruded polystyrene down to the footings, another 1” down four feet, and put a 2” skirt of the same foam extending out about 3 feet horizontally just below grade.
""""I have not paid too much
""""I have not paid too much attention to the basement slab. It will receive radiant heat transfer from the basement ceiling, but my main concern was getting the heat to come through up to the ground floor from the basement ceiling loop."""
you said you are concerned about wether the staple up on the ceiling will transfer to the floor above... no it won't .. or .. not much..
heat moves from hot to cold.. if the staple-up "sees" the cold basement slab below.. a lot of that heat will tansfer to the air in the basement and to the cold slab
to move the heat up to the first floor you have to insulate below the radiant staple-up.. so then the heat will move to the colder floor above
and your basement wil be cold
but your first floor will be warm
not having insulation under the slab , means it will always be a heat sink
But my intention is to heat the basement and the first story at the same time with the one loop on the basement ceiling. The basement has an open stairs and I use the basement space quite a bit. The hydronic loop is on steel hangers and runs about 7” below the bottom of the floor joists. So it is about 14” below the sub floor of the ground floor. This is not a grid of heat tubes, but rather just a perimeter loop set in about 4 feet from the block walls.
This loop heats air that convects around to heat all of the basement air. That air rises and is very warm around the fin tube. It spreads out across the basement ceiling, and heats the sub floor of the ground floor. From above, that floor is noticeably warm to touch in the vicinity of the fin tube. But it is warm enough all over, and some warm air also convects up the stairway.
Then the warm basement ceiling radiates heat directly down and heats all objects in the basement including the slab. There is no insulation under the slab, but the walls are R-20 with 4” of extruded polystyrene on the outside of the blocks. There is also a horizontal foam skirt just below grade, extending out about 4’ from the foundation all around. The skirt prevents heat loss that would normally loop out from under the basement slab and then upward outside of the walls. So, in effect, the skirt insulates the slab.
With extra high insulation values of the house in walls and roof system, it makes it really easy to effectively introduce heat from a limited distribution system. It just spreads out evenly because there is no great loss through the walls and roof.
hanging fin tubes
I'm sorry Kdesign, I'm leery of your heating the basement rather than delivering the heat to the living space of the first floor. Radiant heaters should be about people heating not basements. Radiant systems whether they are at the baseboard or in the ceiings work to make you feel warm. It's about heating your body and secondarily heating the solid objects which may radiate long wave heat into the general spaces. The advantage to radiant heat is that the general atmosphere doesn't have to be as warm as a hot air system since the bodies feel the heat directly and the couch or the desk doesn't have to be warm. I think you will be happier if you bring the heat to the living spaces.
Distributing the Heat
Frank,
What I have got set up here for heat distribution works very well, and I am a stickler for being comfortably warm. And it gets plenty cold outside here in Minnesota in the winter. The heat is going into the living space in addition to the basement. It just goes into the basement first.
But I understand exactly what you are saying about radiant heat, and I am a big believer in it. If you had a room with warmed walls, floor, and ceiling, you could have the air temperature at say 30 degrees F., and make it feel like 70 degrees F. just by turning up the temperature of the walls, floor, and ceiling. That is the magic of radiant heat. A person would have no way of knowing that the air temperature was only 30 degrees.
But no heating system is delivering heat only by radiation. With most heat generators, heat is being transferred simultaneously by the three fundamental mechanisms of radiation, convection, and conduction. Radiation and conduction can be somewhat independent, but you can’t possibly have convection without conduction. One instance of radiation alone would be when the sun warms your body. There is no conduction or convection associated with heat transfer from the sun to an object. Although the object may further transfer the heat by conduction and convection. If the object has conductive mass, it will transfer the radiant heat of the sun to the interior of the object by conduction.
With a warmed slab, there are all three mechanisms operating. There is conductive transfer to your feet when you walk on it. There is conduction to the air film contacting it, and that causes that film to rise, thus creating convection as cooler air falls down to replace the rising warmed air. There is radiation to the surfaces of all people and objects in the room including the ceiling. All of the objects warmed by the radiation to their surfaces then transfer that heat through their internal mass by conduction.
All of those objects that are warmed by radiation to their surfaces and conduction to their internal mass then re-radiate from their surfaces in all directions, including to the walls. All of those objects also conduct heat from their surfaces to the contacting air by conduction, and then create convection loops that spread the heat out to cooler objects by the convective current of the heated air.
Even a force air furnace transfers some heat by radiation. It blows out hot air that circulates around and heats objects by conduction, including walls and ceiling. Then the warmed walls and ceiling radiate heat to any surface that is cooler than they are.
Baseboard heat warms air by conduction and causes convection. But it also directly radiates. Cast iron radiators do the same thing but their effect is less spread out that baseboard. Baseboards and radiators also warm the walls behind them and above them, and then those walls radiate heat.
So what I have set up in the basement is nothing unusual. It is just a distributed heat source that heats the ground floor by conduction from the basement ceiling. It heats the basement ceiling by heating air directly beneath it. The warmed air evens out the heat distribution to the ceiling. The warmed ceiling radiates down into the basement and heats all objects. The warmed ground floor heats upward by all three mechanisms just like a warmed slab with heat tubes in it does.
slab insulation
After reading all of the posts attached to Wen and reading that you use 4" of 2lb/cf of Performguard is the use of foil/bubble foil (calim R3 but reflective) or foil/foam/foil (claim R15)under a slab considered inadequate or ineffective? Could either be used under the Perfomguard or other foam for the moisture/vapor barrier?
doubletroublebubble
Thanks Mike.
I agree w/ Mike ... bubble wrap is largely snake oil product.
RE
This has been an excellent exchange of ideas on this subject. So, based on some of the ideas offered, if I put a fin/tube system in the first floor of a full basement house, then tubing would not be necesssary in the slab of the basement? I live in Alabama where winters are obviously much milder than those in Minnesota.
Andy
I have lived with radiant infloor heat in the slab of our built into the hill walkout passive solar house now for 22 yrs.
Your slab will not get real warm with no hot water running through it.
Think just a bit warmer than unheated tile. Heat up at the ceiling will not warm that floor. In fact with just socks on, it'll do the reverse to your body-radiant cool.
Admittedly, the furniture and all things off the floor will probably be fine-I guess.............
Also, there will be no mass to take on the heat and slowly distribute. If the place is super insulated and sealed, this might not be a problem.
Best of luck.
My objective is to just heat the interior as evenly as possible. Heating the slab in the basement or heating the ground floor of the first story could play a role in my even heating objective, but I don’t think it is essential to what I am trying to accomplish. Certainly, my basement floor is usually not as warm as the first story floor, and that floor may not be as warm as typically might be the case with a hydronic loop buried in a concrete slab or even installed in a framed floor.
But the basement floor does not feel objectionably cold even with bare feet. And the first story main floor is warmer. In the basement, I can feel the radiation coming down from the ceiling. On the ground floor level, all the heat feels 100% even and balanced from every direction.
But the main requirement for my even heating objective is to have a well-insulated house, including the basement. I have approx. R-45 walls in the basement. If the basement were not insulated, but the rest of the house was, then introducing heat into the basement with the intent of heating the upper levels would not be very efficient. This is because a lot of the heat would be lost from the basement walls leaving less to transfer upward.
And if the upper levels were not well insulated, depositing the heat in the basement would overheat the basement before heat would sufficiently transfer through the floor to keep up with the heat loss in the upper levels.
Having a lot of insulation allows the heat distribution system to be simpler. It takes time for heat to spread out by transfer principles in a house once it leaves a distribution point. If there are areas of high heat loss in the structural envelope, heat might be lost before it gets evenly distributed by the natural transfer principles that spread it out.
To overcome that problem, the distribution system needs to squirt the heat into areas where it is specifically needed. However, with high insulation values, you can just drop the heat in anywhere, and it gets distributed by the natural heat transfer principles of conduction, convection, and radiation. It has the time for that to occur because the heat loss to the outside is so low.
Andy
We live in "the basement". The sleeping rooms are on the second floor. Even with the open floor plan, the radiant in the slab doesn't just rise upstairs. Down, very comfortable. Up, pleasant. We only have in floor under the tile (h2o under tile underlay), 2- 4' baseboards in the two remote BR's.
In a basement scenario, with little or no living done there, I probably wouldn't have done heat in the floor........................well, maybe not-there's always a chance at a finished basement.