A true story about hardwood floors and radiant heating

rb_6

Unpublished - for all the TECTs (Thermal Environmental Control Technicians) here at Dan's place...distribute as you like.

Hardwood Floors and Radiant Heating
Copyright 2004, Robert Bean, All rights reserved. Approximately 1400 words



So tell me why you can’t use radiant with hardwood I asked the lovely women in the audience. “You just can’t” she said, “everyone knows radiant wrecks solid wood floors and the only product suitable is an engineered laminate.” For a split second I was grateful for the highly trained speed bumps between my brain and mouth since the solid hardwood covering our radiant floor for over six years looks like the day it was installed. Fortunately I was born with an inquisitive streak and always like giving people the benefit of the doubt so I ask the million dollar question again… “why?” Giving me the all knowing evil eye, and in a tone that made me feel like there was a pointed hat atop my bean, she in a Matrix slow motion syrupy syllables said…”cause the heat will dry it out.” Although she didn’t come outright and say it…I heard the silent words….”you dummy.” I responded using a tried and true communication technique of repeating back what she said, but in an inquisitive tone… “the heat will dry it out?” The return communication technique in her eyes told me I was not only dumb but deaf. I took at quick look at my watch and figured quickly, there was 30 minutes left in the presentation and had to move on to other topics so I followed up the “why?” with, “let me guess you work for an engineered floor company is that right?” A little surprised at my forwardness she came back with, “Well yes, but what has that got to do with it.” So I tell the crowd, my wife and I have solid hardwood floors and radiant as do most of my clients and all we can say is someone owes us a great big check because if radiant wrecks solid hardwood and only the laminates work then evidently we all have laminates but paid dearly for solid - so I’m thinking - call the hardwood police - we’ve been ripped off. What do you think happened to us? Backing down a bit from her passion she says, “I don’t know…all I know is what I’ve been told.” Ah ha herein lays the lie and the time to expose the truth.



I remind the audience we have about two minutes to cover the facts so let’s get them out on the table. Wood is a hydroscopic material which means it’s like a sponge. It absorbs moisture and release moisture based predominantly on relative humidity. If the wood is dry and the room is moist the cells in the wood will absorb whatever they can and in the process expand. What’s more, if the room is dry and the wood moist then the cells release the water and contract. That’s it…the expansion and contraction in hardwood is nothing more than a change in moisture content and water vapor, and just like temperature and pressure, moisture always goes from high to low. I didn’t make this up, moisture specialist, Donald P. Gatley, P.E. says this in his authoritative book on moisture, “The equilibrium moisture content of materials is almost solely dependant on relative humidity and is largely unaffected by temperature.” So who am I to argue with a man who gets paid to study water vapor? So it doesn’t matter if it’s a furnace or radiant heating…consistent moisture control is our numero uno focus.



At this point I ask the audience, “so does anyone want to know why the radiant hardwood floors I’m familiar with, look absolutely exquisite?” Most hands go up so I take this as a signal to layout what is necessary for the marriage between radiant and hardwood to work.



First let’s look at how lumber is milled. Boards are cut from the log either as “plane sawn” or “quarter sawn” materials. Hardwood, milled as plane sawn has its grain running parallel with the sub floor. Quarter sawn wood has its grain running perpendicular to the sub floor. The reason why this is so important is wood expands more across the grain than with the grain. In fact, according to the wood scientist, wood changes approximately 0.1% along the grain in quarter sawn lumber and 5% to 15% across the grain with plane sawn. At this point I pause to let this information sink in….think about that I suggest… “5 to 15% for plane sawn and only 0.1% for quarter sawn”… I ask, “can anyone tell me what type of cut we should be specifying for our radiant floors?” Now the audience is paying attention because this makes a lot of sense as most things which work do…so I lock their thoughts in with this quote from the folks at www.bchardwood.com, “…the benefits to this (quarter sawn) cut of wood are straighter grain that is up to 50% more stable than plain sawn flooring, and a superior looking product featuring less variation, longer lengths, and medullary rays.” Once everyone agree this is a no brainer, we start talking about wood variety because certain species such as teak, oak, cherry, walnut, mesquite, and others are known for their dimensional stability whereas maple and beech exhibit more movement in response to moisture changes…and just so everyone knows I’ve been doing my homework I point out the extensive laboratory testing by Launstein Hardwood Floors in Mason, Mich., who agree with the list of recommended species. Finally we get to the short list of other recommendations such as use narrow widths (less than 2.25”), use boards with beveled edges and darker stain colors which conceal shrinkage crack between boards better. Last but not least we cover off the procedure to introduce hardwood to its new permanent place in the home….



Before Bringing Hardwood to Site Check List:



All concrete slabs should be 28 days or older before bringing in flooring.

Ensure any moisture producing trades such as wall boarding, plastering and painting has been completed for at least 48 hours.

Ensure environment is at normal living conditions with the HVAC system operating for at least 48 hours and the humidity stabilized to the yearly setpoint, typically between 30 to 50% RH.

Ensure sub-floors are clean, dry, cured and environmentally stable and verify with both moisture and temperature test according to NWFA procedures, Section V,a-1,5,6

Ensure a 6-8 mil vapor barrier is installed and sealed over cementatious substrate.


Delivering Hardwood to Site Check List:



Hardwood delivered to the home must be divided into small lots and placed in the rooms where it is to be installed.

Acclimate wood flooring 7 to 10 days before installing
NWFA recommends wood flooring to be within 4 percent of sub-floor before installation is safe.

Professional installers carry moisture meters with them and will perform the test according to NWFA procedures.

Prime all four sides of kiln dried hardwood before installing.




During and After Installation Check List

Wood which has been cut or mitered should have ends sealed with a transparent sealer before installation.

Let wood flooring further acclimate before sanding and finishing, 4 to 24 days depending on regions.

Finish floors to specifications

Use a suitable radiant floor control strategy to gradually raise and lower temperatures based on heating loads and weather conditions.

The floors surface temperature should be operated to less than 85 ºf (30 ºC) and rooms constantly maintained at a nominal 40% RH based on comfort and health researchers Dr. Fanger and Dr. Elia Sterling.


That’s it…really most of it is common sense and applies to any type of heating system, not just radiant floor heating.

I close of this seminar topic with a reminder to expect resistance from the amateur installers and expect to pay less for plane cut timbers and some species of wood. Putting the amateurs together with a low budget will always and exactly deliver the lie that gets spread around the industry. If you want the truth you have to pay for the reality which means using professionals and good methods and materials. On that note we moved on to the next topic of interior environments for health, wellness and comfort.

Thanks to Dan Peel for inspiring these words...he was in the audience this spring and was there with some great information.

_________________________________________________________

I'm thinking we already have a Carlson - Holohan award - how about a permanent web based memorial hosted by ___ _______(New Yorker...glasses...just admitted he's a blogger...know anyone like that?) Just a thought...imagine our kids and kids kids coming here to see where the industries finest used to hang out...kind of like a cyber pub...with all the superstars hung up on the --- (you guessed it) --- the Wall.

Just a thought.

Steve_OH

Your numbers aren't quite right

The 0.1% number you give for movement along the grain is just that: ALONG the grain. In other words, lengthwise along the plank. That number is no different for quarter-sawn vs. plain-sawn. There is a definite advantage to using quarter-sawn lumber, but the difference between quarter-sawn and plain-sawn is only about a factor of two, not a factor of 100 (the exact ratio depends upon the species). For example, if you're using northern red oak, the tangential shrinkage (plain-sawn) from green to 6% moisture content (MC) is 6.6%, and the the radial shrinkage (quarter-sawn) from green to 6% MC is 3.2%.

6% MC is pretty typical for wood stored indoors. I recommend _Understanding Wood_ by R. Bruce Hoadley for everything you ever wanted to know about how wood moves as humidity changes.

-Steve

Duncan_16

green wood

What exactly do you mean by the term "green" wood, in the last sentence of your first paragraph, Steve?

When I hear the term green wood, I think in common terms as in firewood. In this sense of the word, green means the sap and the interior of the wood has never had a chance to dry from the time it was cut down as a living tree. Drying to the center of the wood is accomplished either with time, or with kiln drying. In either case, attention is paid to moisture content throughout the process to avoid checking (cracks).

I'm thinking you'd be fairly hard pressed to find green wood from a commercial lumberyard, unless they're buying from local mills. Isn't most commercially available, milled flooring kiln-dried?

Just want to make sure I understand the term correctly, that we're comparing apples to apples.

Constantin

It always amazes me how propaganda can work...

First off, thank you for the article. I think it's a good piece and it illustrates how certain "truths" get propagated and never get challenged. Groupthink, et. al. at work... and it was particularly egregious for someone from the laminate industry be spouting off like that, an obvious conflict of interest.

When the time came to rebuild our house and install a new heating system, I knew that it would be radiant heat, covered by hardwood. My mum's place has had it for years, and there are no issues with that building... you simply have to know an hour or two in advance that you're going to use a room - some rugs, and a lack of insulation between floors slows the response time... ;-)

Yet, time and time again, some people try to tell us such a system won't work... as a Chinese proverb puts it: "Those that say that it cannot be done should not not interrupt the ones doing it" (or something like that).

Anyway, thanks again for the anecdote and the recommendations. I will print them for our builder, which will probably move forward the date of delivery for the oak so that the stuff can properly season and dry in the warm basement... which has dried on it's own accord for the last 5 months. BTW, I am happy to report that the concrete basement slab has CRACKS (gasp!) ... in all the right places. Looks like our expansion strip strategy worked perfectly.

Dave Yates (PAH)

RxB, your timing is...

perfect!

I have an early AM meeting with homeowners who are scared stiff our radiant heating will ruin their hardwood flooring. The flooring contractor won't let up and has been braying to anyone with an ear that we'll ruin the hardwood. So much so, that the owners commented "Now we're stuck with a system that will warp the floors"!

When I ran the numbers on the first floor (it's two floors of radiant), we were riding a knife edge for upper limits, so we added a two-stage (heating side) stat and a hydronic coil in the ductwork. Good thing we did because the Mrs. went out and bought a Persian rug. No problem though as we can tweak the hydro-coil response by lowering the floor circuit delivery temperature (did that anyhow because I didn't want to run at limit temps).

They changed to carpet on the second floor - even though they'd wanted hardwood - again due to the installer's comments. This, in turn, changed our needed delivery temps and we then split this off with its own zone and thermostatic control.

Like any snowball rolling downhill, this then threw off the master bath temps (tiled floor) and we set it up on its own zone too.

A Munchkin with Vision-1 rides the heating curve while 3-way mixing valves dumb down as needed in the lower temp zones.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

steve b

wood shrinkage

I agree, Hoadley's book is excellent.

Quarter sawn wood certainly is more stable, but also more expensive.

The bottom line: if you want a wood floor that stays flat and doesn't gap, thoroughly acclimate the wood to the house atmosphere before installing, and then keep the humidity level constant year round at the acclimated level.

If you don't humidify the air in the winter, and allow the RH to drop, and then open windows during the humid summer you will see a wide range in humidity and much expansion and contraction of the wood -regardless of the type of heating system. Some of the best wood floors you'll see are in museums and galleries that tightly control temperature and humidity.

Of course, to avoid stressing the wood you want to limit the temperature in a radiant floor.

rb_6

Thanks for the information

Thanks all for the comments and suggestions...the article is intended to motivate consumers to do some homework before spreading the tale...

We deliberatly left out topics on EMC (Equilibrium moisture content), FSP(fiber saturation point)and DCC (dimensional change coefficients) basically any points a wood specialist would understand but a consumer would (wood) roll their eyes at....and decide to use anything but solid hardwood.

But if you want all the details...the book recomended by Steve is great as are other sources such as the Canadian Wood Council et al


The exact phrase for the text in question is taken from a number of sources and most read something like this:

"Between the fiber saturation point and the ovendry state, wood will only change by about .1 percent of its dimension along the grain (lengthwise in a flatsawn board). It will change by 2 to 8 percent across the grain and across the annular rings (top to bottom), if quartersawn; and 5 to 15 percent across the grain and parallel to the annular rings (side to side), if plainsawn."

"The ideal moisture content for flooring installation can vary from an extreme of 4 to 18 percent, depending on the wood species, the geographic location of the end product and time of year. Most oak flooring, for example, is milled at 6 to 9 percent."

Steve_OH

Green wood

"Green" in this context means "fully saturated with moisture." It's what you'd get if you soaked the wood in water for several days.

I agree that wood flooring is never sold green, and I apologize if I implied that it was. The point I was trying to make is that overall, the shrinkage in quarter-sawn lumber is half as much (twice as good, in a sense) as it is in plain-sawn lumber. The reason I used the numbers that I did was because that's the way the tables are always given, shrinkage from green to whatever. The basic idea, though, is that the ratio of tangential to radial shrinkage stays pretty much the same, no matter what your starting and ending points are. In any given situation, quarter-sawn wood is always going to shrink half as much across the width as plain-sawn wood. (Conversely, quarter-sawn wood shrinks twice as much across the THICKNESS as plain-sawn wood does, but that's never a problem in a floor, of course, although it does play a role in furniture, cabinetry, etc.)

Let's look at a more realistic example, for a house without humidity control: Let's say worst case low humidity in winter is 25%; equilibrium MC under those conditions would be 5%. Worst case high humidity in summer is 75%; equilibrium MC under those conditions would be 14%. (These are average numbers; again, there are slight variations from one species of wood to another.) Using red oak as our material, we find that the shrinkage going from 14% MC to 5% MC is 2.8% tangential, 1.2% radial.

If we're using 2" strip flooring, that works out to a variation from summer to winter of 0.056" (nearly 1/16"!)across the width of a plank for plain-sawn, and 0.024" for quarter-sawn. Even with the quarter-sawn, you're going to end up with noticeable gaps between the planks, but they'll be only half as big.

The bottom line is that as the original poster pointed out, you need to control the humidity! That's true even if radiant heating is not part of the picture. Radiant heating DOES exacerbate the situation, since a warmer floor means a drier floor, and at a time (winter) when the floor is already at its driest, but if you control the humidity, it won't be a problem. Quarter-sawn lumber gives you some extra insurance against shrinkage, but it's not magic--what it gives you is only a factor of two, and by itself it's not enough.

-Steve

Unknown

Great timing Robert

This answers lots if questions I had just a couple of weeks ago here:


http://forums.invision.net/Thread.cfm?CFApp=2&&Message_ID=137925&_#Message137925

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

S Ebels

In my humble experience

These things are mandatory for a successful radiant hardwood install.

1. Constant circulation. This does away with sudden bursts of temperature hitting the floor.

2. A system that evenly distributes the heat. Any thing that allows more than a 1 to 1.5* degree variation across the floor raises the odds of having a problem.

3. Reasonably controlled humidity. I have never seen a problem with a wood floor that could be blamed solely on high temps. Moisture entering and leaving the wood is what makes it move.

4. Acclimate the wood. The longer the better. Minimum of 3 weeks at local ambient conditions. Acclimate means, take it out of the boxes, spread it out, lay it flat and let it sit there allowing the moisture in the house and the wood to equalize. Don't just haul it in the house and leave it stacked up in the cartons.


I have said this before here regarding my own 3/4" solid wood floor but I'll repeat it. I have purposely abused the floor in my living room, (3/4" solid birch) by driving the temp as high as 95-96*. It is installed over Stadler Climate Panel (7" spacing) with constant circulation via a Divicon mixing system. In spots where the sun reaches in for long periods (3-4 hours) the temp has been measured at a couple tenths 100*. The floor has not moved. Late in the winter I'll notice very small gaps, 1/64" to 1/32", when the RH in the house is at its lowest. This would be around 20%. After running it that hot, I don't think I have any reservations about recommending radiant, solid wood floors to anyone.

Mark Eatherton1

Thank you Robert!!

You are a scholarly gentleman!

ME

Floyd_7

Silly people.....

They will rant and rave about radiant heat.....
but still will install a hardwood floor over an unheated, damp crawl space, in a house with scorched air heat......

Ever run over a rumble strip on the highway?????

go figger....

Floyd

Duncan_16

Crazy woodheads.

Seems to me, it'd be a more precise use of language to call what you're describing as wet wood. But I s'pose every trade has it's own language.

Once I saw $30,000.00 worth of uncured (that is, "green") white oak laminated counters torn out of the Bear Mountain Inn at Bear Mountain State Park in NY State in the 70's because they'd used green wood to build them. Seems white oak was so hard to get they had to special order it. They were in a hurry. The counters all checked and were ruined. Pretty special.

As a wood guy, you'll hate this. As I recall, the geniuses in charge of the remodel tore out huge pieces of American Chestnut that were installed at the turn of the century. Full tree posts, railings, etc. Lovely. I never did find out where that wood went.

Duncan_16

Fully saturated with moisture.

Seems to me, it'd be a more precise use of language to call what you're describing as wet wood. But I s'pose every trade has it's own language.

Once I saw $30,000.00 worth of (I'm pretty sure) white oak laminated counters torn out of the Bear Mountain Inn at Bear Mountain State Park in NY in the 70's. They'd used green (uncured) wood to build them. Seems white oak was so hard to get they had to special order it. They were in a hurry. I guess the guys at the mill were too. The counters all checked and were ruined. Pretty special.

It gets worse. As a wood guy, you'll hate this. As I recall, the geniuses in charge of the remodel had huge pieces of American Chestnut that were installed at the turn of the century torn out to "modernize" the place. Full tree (big!) posts, and beams, railings, etc. Lovely. I never did find out where that wood went. It scarred me for life, I tell ya, I haven't been the same since. Because of that I drink and write bitter early morning emails. Grrr.

Mitch_4

proverb

I think the proverb you are thinking of is:

"those who think they know everything annoy those of us who do"

I am I mis-remebering the applicable proverb?

Kal Row

someone should have shown this lady bamboo floors...

they are beeeeutifull and a perfect fit for radiant...thin, strong, really low resistance, and minimal expan/contrac on temp or moisture - they use bamboo scaffolding on ski-scrapers in the far east, if it changed size/propoties a lot from day to night or rain/dry it would be useless

would love to know if any of you had a problem with a bamboo floor and radiant

rb_6

Guide Reviewers wanted


If any of you folks would like to review our soon to be released : Guide to Hardwood Floors and Radiant Floor Heating,

Please contact me.

Thanks for all your comments and feedback!

Duncan_16

\"fully saturated with moisture\"

> "Green" in this context means "fully saturated

> with moisture." It's what you'd get if you soaked

> the wood in water for several days.

>

> I agree

> that wood flooring is never sold green, and I

> apologize if I implied that it was. The point I

> was trying to make is that overall, the shrinkage

> in quarter-sawn lumber is half as much (twice as

> good, in a sense) as it is in plain-sawn lumber.

> The reason I used the numbers that I did was

> because that's the way the tables are always

> given, shrinkage from green to whatever. The

> basic idea, though, is that the ratio of

> tangential to radial shrinkage stays pretty much

> the same, no matter what your starting and ending

> points are. In any given situation, quarter-sawn

> wood is always going to shrink half as much

> across the width as plain-sawn wood. (Conversely,

> quarter-sawn wood shrinks twice as much across

> the THICKNESS as plain-sawn wood does, but that's

> never a problem in a floor, of course, although

> it does play a role in furniture, cabinetry,

> etc.)

>

> Let's look at a more realistic example,

> for a house without humidity control: Let's say

> worst case low humidity in winter is 25%;

> equilibrium MC under those conditions would be

> 5%. Worst case high humidity in summer is 75%;

> equilibrium MC under those conditions would be

> 14%. (These are average numbers; again, there are

> slight variations from one species of wood to

> another.) Using red oak as our material, we find

> that the shrinkage going from 14% MC to 5% MC is

> 2.8% tangential, 1.2% radial.

>

> If we're using

> 2" strip flooring, that works out to a variation

> from summer to winter of 0.056" (nearly

> 1/16"!)across the width of a plank for

> plain-sawn, and 0.024" for quarter-sawn. Even

> with the quarter-sawn, you're going to end up

> with noticeable gaps between the planks, but

> they'll be only half as big.

>

> The bottom line

> is that as the original poster pointed out, you

> need to control the humidity! That's true even if

> radiant heating is not part of the picture.

> Radiant heating DOES exacerbate the situation,

> since a warmer floor means a drier floor, and at

> a time (winter) when the floor is already at its

> driest, but if you control the humidity, it won't

> be a problem. Quarter-sawn lumber gives you some

> extra insurance against shrinkage, but it's not

> magic--what it gives you is only a factor of two,

> and by itself it's not enough.

>

> -Steve

Duncan_16

\"fully saturated with moisture\"

No wonder I got confused. Seems to me a more precise description would just be to call it "wet". Then "green" could mean newly harvested and uncured. So it's a trade term the wood guys use, not common usage. Gotta respect that.

Here's an experience with uncured wood for you, as well as a wood disaster.

In the 70's I saw $30,000.00 worth of newly installed uncured (I think) white oak, laminated counters in place at the Bear Mountain Inn at Bear Mountain State Park in NY State.

If I'm remembering correctly, white oak (if there even is such a wood) was difficult to find at the time, so it had to be special ordered from a local mill. The counter makers were in a hurry, and evidently so was the mill. The wood was green in the sense of the word I use. The wood in the counters checked across the grain and I believe were eventually redone or replaced. Special.

The REAL disaster is that the geniuses whose aim was to "modernize" the look of the place tore out huge (whole tree diameter) posts, as well as beams, railings, etc of 60 year old AMERICAN CHESTNUT !

That experience scarred me for life. I haven't been the same since. I still wake up in the middle of the night shaking with cold sweats, wondering what ever happened to that wood?

The bottom line I got from Robert's original post is that the heating guy pretty much has to know more about solid wood flooring than the UNinformed flooring guys !!! I'm thinking knowlegeable flooring guys know the score.

Keep makin' sense, boys. Glad we got that bubble foil thing straightened out, too. Two down, twenty-three eighty myths to go.

Steve_OH

Horror stories

We read lots of HVAC horror stories here, but there are plenty in the construction side of things, too. I remember reading one not too long ago: The author was visiting a home under construction as the installer for the kitchen cabinets was going about his business. The installer was building frames out of 2x4's to set the base cabinets on, and the author noticed that they were sopping wet. (It turned out that the installer had gotten them from a stack that had been sitting outside, uncovered, at the construction site.)

He mentioned to the installer that they would shrink about 1/4" when they dried out, and if he set the base cabinets on them and then fastened the cabinet backs to the wall, the fronts of the cabinets would end up 1/4" lower than the backs. The installer replied that this was the way he always did it, he never had any problems before, etc.

The author came back about a month later, when the house was just about done, and went into the kitchen, where he adminstered the "pencil test": You lay a pencil down on the countertop, and see if it rolls. Sure enough, the counters were way out of level, so much so that if you knelt down and got them at eye level you could easily see it.

So the end result is that whenever the homeowners spill something on the counter, it will end up on their feet within seconds.

-Steve

Plumdog

rb: I'd be happy to be a reviewer of your guide on hardwood and radiant. How can I contact you?