I am going to build a 20×26 shop attached to the garage. Would like to put in radiant heat in the slab, but would like to have a wood floor. Would a floor of 2×4 sleepers (laying flat) covered with 3/4″ plywood be ok on top of the radiant slab? In other words, would the heat “get thru” the wood?
Thanks,
Paul
Replies
eventually at a reduced output..
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WOW!!! What a Ride!
Forget the primal scream, just ROAR!!!
I'm not a radiant floor guy but my first thoughts are, if you're going to put down sleepers, why don't you put the radiant heat between the sleepers so you won't have to heat the whole slab. You could even add some insulation under the plumbing and over the slab.
using a floating floor would be the best bet.
two layers of wood is generally doable, it'll raise your water temperatures a bit though.
as always, it depends on your heat load!
remember slab is a mass system.. doesn't turn up or down immediately, if this is a part time shop.
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Like NRTRob said, it is possible, you are heating mass and the more mass the greater the response time of the system. The thinner the sleeper the less of an air gap, the lower the system temp and the shorter the response time.
gotaal10
The R value of wood is about R1 per inch. Understand that R value doesn't prevent the transfer of heat simply delays it..
If you warm up a chunk of wood eventually the whole chunk of wood will be at the temp it's warmed to.. less any loss in radiation..
So if the concrete gets to 90 degrees the wood will eventually achieve 90 degrees less radiated temps.
Frenchy,
this is a strange statement. "The wood will eventually get to 90 degrees, minus radiated temps".
That means, it will never get to 90 degrees. It may not ever get anywhere close to 90 degrees if the heat load pulls heat away faster than you can push heat through the floor. The R value of the floor is not irrelevant to efficiency or ability to transfer heat. It is quite critical, in fact. Put an R5 floor on and you're unlikely to ever be able to get enough heat through it to keep a room warm in a real heating climate, for example, at any water temperature you are likely to be able to generate.
Energy is conserved, but what you're thinking (the heat will get there eventually) is not useful in heating system design or in thinking about heating systems. Heating systems are about delivering heat in a certain quantity over a certain period of time. Both quantity and time are important factors. Doesn't do me any good to take all year to provide an hour's worth of heat to a room, to use an extreme example to illustrate the point.
So in the real world, R value does prevent the transfer of heat. If it didn't, insulating your house wouldn't save you any money. But it does... why? because you lose less heat over a period of time, with R value slowing down how fast the heat "leaks" out. A "winter" is a period of time.. several months. With more R value, less heat Leaked out, even though eventually all the heat leaked out, while it's hanging around it's keeping you warm. More R value kept it hanging around longer, so you didn't need as much.
I'm responding to this because I see very misleading claims by reflective insulation manufacturers all the time about this, acting like R value doesn't do anything and that reflectivity is the only real way to avoid "heat loss", and your statement sounded just like them, so I don't want anyone reading to have a seed planted about R value that is totally wrong. The idea that R value only delays heat loss, while technically accurate, is not a useful way to think of heat transfer. You can never forget that time is just as critical as BTUs in the heat transfer equation.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
NRTRob,
I understand what you are saying and I can't disagree with it. Yet if you heat up something and that something yeilds it's heat thru radiation or other ways of transferance it is making a contribution towards warmth. It's sort or the princple of a soapstone wood stove. The radiated heat of the wood burning is prevented from entering the room by the absorbtion process of the soap stone.. it is eventually released over time as the room cools below the temp of the soap stone.. The same happens with solid wood.. heat is absorbed and eventually released..
Words like thermal mass enter here. and we can be extremely scientific about it but for our purposes. it should be enough to say that heat will travel thru most solid items reasonably well and thru insulation with it's air barriers less well.. short and simple the differance is R value.. Copper has a extremely low R value,, foam has a high R value..
Dense solid wood has a lower R value than softer woods do (Oak will transfer heat quicker than pine will) so a floor made with a hardwood will transfer heat quicker than a pine floor will.
I believe that a floor made of hardwood will radiate heat better than a floor made of plywood and carpeting.. My sub floor is a hardwood called tamarack on top of that is another hardwood either maple (hard) or black walnut..
The black walnut will be slightly cooler than the hard maple because hard maple is a more dense wood than black walnut is and thushave a slightly higher R value..
Both will transfer heat better than the same thickness in carpeting
But there is a big difference between your soapstone stove and a wood floor: The soapstone is a lot better at conducting heat than wood is. It has a lot of MASS, so it can store a lot of heat, that complicates things. But still, it conducts well. If it didn't.. imagine it was a stove made of unburnable foam... most of your heat would go up the chimney. You aren't getting around R value and conductivity, you're just slowing down the initial transfer rate because you have to charge up the mass first before it will shed its heat as fast as it is absorbing it (you raise its temperature so it sheds heat faster, until it heats equilibrium with the room temperature and fire's burn rate). And when you are done adding heat to it, you have a whole lot of mass that has heat to lose before it is room temperature again. Wood is not that great at conducting heat. You are adding significant resistance to heat transfer, when you add layers of wood. This means you are actually slowing the rate of heat transfer down, not just delaying the beginning the transfer and extending the end, but actually slowing down how fast heat can EVER travel through the material. Yes, the wood will absorb some heat and eventually it will give it up (but it doesn't have that much mass, so that's not worth thinking about really), and it will conduct heat. But adding layers of wood is not insignificant.All I'm saying is adding layers of wood is not insignificant. Look at underfloor heating systems... even with heavy plates. With a high heating load... but not so high that it would be very unusual... your water temperatures start getting higher than some heat sources can provide, even with only a subfloor and wood finish floor. and concrete doesn't conduct as well as aluminum does.... probably not the case here, but still. I have seen systems fail because the builder didn't understand that he can't just add layers of wood without checking first.You seem to understand it, it's just the language I see you using seems a bit off... and again, similar to those reflective insulation claims I keep seeing that drive me nuts, so this isn't really about you in any case heh... hope I'm not sounding TOO nitpicky..-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
NRTRob,
No, I do understand the differance and frankly you make sense. I realize that I am not using verbage common with your industry.. in part because I like to try to eliminate jagon if possible.
I also realize the trade offs, in my example the loss or trade off is the fact that too much heat may escape up the chiminey, instead of into the room as intended.. in the case of usage under a floor with say thick carpet on it. heat may be"sent" to someplace where it's not needed as much.. but no heat isn't really "lost"!
As long as heat is retained inside the building envelope* it has value.. I understand the pleasure of standing in front of a roaring fireplace and feeling that warmth, Yet realize the cost of that roaring fireplace is greater energy consumption than what the fireplace may provide..
With the advent of forced hot air the "roaring fireplace" became available to every room but at a cost. The cost was drafts and stratification of temps..
At least with in floor radiant heat we have the heat where it really needs to be. We can discuss transferance and radiation etc. the only question becomes how much is required to be comfortable.. Since the permutations for that calculation are endless. In my humble opinion the most efficent method will be to start short of the intended goal and work our way up to the smallest amount needed.
I realize that commerical contractors can't do that so they are required to oversize the system to ensure that something wasn't overlooked.
I'm in the unique position of being able to use two systems. My old forced air system as back up and my new in floor radiant systemn as my own test lab.. if my calculations should prove to be in error the back up system of forced air will provide comfort while I adjust my new system.
IN the case of the OP heat that is released into the floor (assuming proper insulation under the concrete) remains in the building only as long as the insulation package retains it.. with a poor insulation package heat loss may be greater than heat requirement. thus failure!
Are you doing a wood floor so it is easier to walk on? You could just pour a slab then use rubber mats in the work areas.
I like Jeff's idea the best. But if you must have wood, did you mean that the 3/4" plywood was the finished floor or a subfloor for hardwood? If it were the finished floor, you could dispense with the sleepers and use thinner plywood, such as 3/8".
In any case, make sure you have 2" of insulation under the slab. You may want to have an outlet in the slab for power for your table saw, too.