Building a new house with radiant floor heating, can’t decide whether to put the tubing into sand between 1 x2 sleepers with plywood on top or to mix Portland cement with sand to make a hardening mixture onto which we will apply tile directly.
Anyone know which is more efficient? And easier ? (we’re not getting any younger!)
Thanks!
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Replies
As with most subjects, I know just about enough about this to be dangerous, but I would think if you have too much thermal mass that it will take too long for the floor to reach a temperature where it will begin to radiate heat to the occupants. Then if you want to turn it off, it will be a long time before it cools down. There must be an optimal mass for the system. (But I don't know what that would be.)
There are many options for installing imbedded tubing between a subfloor and a finished floor, sand & sleepers being about the worst. For a tile or stone finished floor covering, I prefer the lightweight concrete overpour, such as Maxxon's Thermafloor product http://www.maxxon.com/product_detail.asp?ID=4 .
There are a bunch of us here who believe that in a practical sense, you cannot have too much mass. No worries about ramp up/down times, assuming the structure is designed in its entirety as a system designed for this. Heck, Tom's house has essentially a year long ramp up/down time and works well. But sand is not the means to do this.
My own beliefs are that you go either high mass (thick slabs, mass walls) or you go entirely low mass (Warmboard or equivalents) and skip the middle ground of gypcrete/thin slabs. But whichever way you go, pay as much or more attention to the envelop and controlling unwanted air infiltration, controlling moisture content, etc. These have as much of an effect on comfort as your implementation of RFH.
I concur with the previous posters, sand is a poor radiant transfer medium. However I see no problem with thin pours of concrete.I also see no real benefit to mass unless you are doing passive solar, off peak charging, or other techniques that require heat STORAGE. Mass Stores Heat, it has absolutely nothing to do with efficiency of heat transfer. Naturally if you are pouring a slab anyway, it would be ridiculous not to use it for radiant in most cases, but there is no reason to consider mass systems only when considering how to do radiant except for heating methods requiring storage of heat (time shifting of loads).If you don't need to store heat, then mass or the lack of it is just another factor to consider in your controls methodology.-------------------------------------
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Speaking of mass.
I have not yet gone thru a heating season in the finished house though I am sort of looking forward to it. While under constuction the RFH worked great keeping the house dry and warm but got $$$ being unfinished.
Anyway, this years cooling season is upon us. I'm finding that cooling is easier and lasts longer with all of the gypcrete in the floor. Can I expect this to continue or is it only because I'm only there on weekends? The odd part to me is that even when first walking into the house, it's much cooler than the outside after being closed up for a week or more.
Do you have any insight?
cool basement in a well sealed envelope? Best guess I've got..-------------------------------------
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I concur with the previous posters, sand is a poor radiant transfer medium.
I've heard this in several places on this board (from people who definitely know more than I about this), but if sand is such a poor radiator of heat, then why do you burn your feet on it at the beach?
I'm not claiming to know more than the experts, I'd just like to understand the physics behind this.
Edited 7/5/2006 2:56 pm ET by Soultrain
Thanks to everyone, I appreciate the input!
I should explain a little further. We live in Northern Canada, so amount of time to heat/cool floor isn't much of a problem - I hope it heats up in October and stays that way 'til May!
Initially we were going to staple the tubing up to the underside of the main floor with the aluminum fins but the design of the house - maybe calls for a little more efficiency in one particular area.See, the house consists of (3) 20 ft. by 20 ft. pods (with basements) placed in a triangle formation and the living/dining area is a floor that is suspended from the pods about 7 ft. up in the air like a bridge, there will be a sort of dry gully running underneath this area. So in the pod areas the upper floor is above a heated basement, the living/ dining area has cold exterior air beneath, albeit on 14" TJI's packed with insulation. Also, tall ceilings and lots of windows especially on the North side. So, we're wondering if more radiant mass is required for this area, or if it's not worth the effort. We are using a Takagi on demand water heater for the RFH and domestic hot water.
One of the pods will store water cisterns in the basement, 3600 gallons.
I would attach a picture if I knew how!
First, you burn your feet at the beach specifically because it doesn't conduct heat very well. Dig your feet a few inches into the sand and suddenly it's not hot anymore.. if it was conductive, the whole mass would be heating up. Instead the surface heats up quickly and the rest much more slowly.Second, Puzzle it sounds like you are committing several errors here. First, a Takagi is not a great radiant heat source. Second, you are about to install a fairly expensive heating system and no one has apparently done a real heat load calculation or you would KNOW what you need where.This is a big no-no. Don't install a foot of pipe without a load calculation. Otherwise you're just guessing, and as you are seeing, guessing is no way to design a heating system.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Thanks, Rob.
A load calculation was done (a year ago) but because we are slow builders, we've since had too much time to think! At the time they calculated we were planning to use the staple up system, but they told us that in this zone on the coldest days (-40 ish)we would possibly have to turn up the water temp a bit as we couldn't fit any more rows of tubing between the joists @19.2" on center. Sorry, I don't have the figures here- I am at work (self employed not just goofing off!)
So, in the meantime we were thinking that we'd get better efficiency by putting the tubing above the floor in a better radiant mass under the floor tile. Also that way we could probably add more rows of tubing as we wouldn't have to contend with running between floor joists.I do know that we'll have to consult with them again before we proceed...
We already have the Takagi, but we figure even if it's not up to the task we can add another. Although the house is not very big in terms of sq. footage (1800 sq. ft. on main floor) but we do have long distances to span- the house is 80+ ft. wide and 56 ft. deep at the outermost points.
Thanks again!
Puzzle
Are you using heavy gauge plates in the joists?-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Hmmm, don't know- here's a picture
http://www.radiantcompany.com/prices/prices.shtml
Sorry, don't know how to attach a proper link!
Thanks.
Puzzle
Those are lightweights.Use Radiant Engineering's Thinfin or Thermofin plates (assuming you're using 1/2" pipe, I hope), or Uponor/Wirsbo's Joist Trak, or RTI's Radiant Trak in the higher load areas at least.You can get a good 30 degree water temperature drop using those ... much better at heat transfer.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Thanks very much, Rob.
We have a few other issues that are too lengthy to go into here.
I was just looking at your website, think we'll give you a call- not looking for free advice but I think we want a second opionion on what we have in mind.
I heat my home with a Takagi. I have for 4 years. It also provides all domestic hot water. We have a 2.5" stained cement floor on joists. Most of the winter we have the temp on the water heater set at 110 degree's. We bump it up when the temp goes below -25.
The floor heat usually kicks on around 4 or 5 in the morning. It might run once or twice in the late afternoon, if it is really cold or we have the door opening alot. Our house is built with SIPs.
This makes for nice warm floors in the morning and we never ususally have to have the heat over 67 to be comfortable.
Jill
Oh, good to hear it! I had been worrying a bit about our choice of heat source. But I figure even if we had to add another Takagi it would still be cheaper...
Thanks!
Puzzle
just because it heats the house doesn't mean they are heating it nearly as efficiently as they could be with a proper heat source, and the action of their radiant system is far from ideal if it's only coming on a few times a day.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
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I understand that, too. But it's always encouraging to hear that at least they're not freezing to death! (You have to understand that while we've been building we've been living in a 14' x 16' cabin on the property with rudimentary heat, electricity and water- so we have reached a point where it takes very little to impress us!)
We've had a LOT to debate and are just slowly reaching a consensus as to how we want to proceed.Will talk to you this week.
Thanks
Puzzle
It's all good, there are just a lot of systems out there that are "working great", that missed the boat by a mile. But they heat a room and so people are thrilled, not knowing "what could have been".Thus anecdotal evidence is always tricky ;)-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
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"the action of their radiant system is far from ideal if it's only coming on a few times a day."
Can you explain that? Our system only calls for heat a couple of times a day. Why would that be a problem? I would say that means we have a well insulated system that holds it's temperature well and only kicks on when it needs to.
The most efficient system is one that replaces BTUs lost exactly, typically. Certainly the most comfortable operation is one that is continuous.If it's only slamming on a couple times of day, the mass is balancing it out to some degree, but you are not getting the even operation that would maximize both efficiency and comfort.On a takagi though it's probably better since takagis would do a horrible job at more continuous operation. But that doesn't make it a better operation, just a workaround for a substandard heat source.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Oh, oh! Horrible???
I would agree that running the Takagi non stop is not good! IF your system will need to cycle on and off many times a day and heat the water 40-50 degrees or more each time then I would chose something different for a heat source.
My house is very well insulated and sealed and holds it's temp. very well.
I still don't get that.
You are saying that I should have a system that is constantly working and burning energy because it is more comfortable?
Using that as an example, you are saying that a forced air furnace should be always on so that I am more comfortable?
I am missing something here. My heat turns on only when I need heat. I am not uncomfortable in any way. I only burn what I need not any extra, therefore I save money. I think there would be somthing wrong with my home if I had to have the heat constantly running.
My Takagi also only heats the water to the temp. I want. It does not heat it hotter and therefore I do not add any cold water to the system. Therefore I save.
What am I missing? I am not an expert just a homeowner.
You're thinking of operation as on/off. Either ALL ON or off. In years past, that was the only operation available and you'd be right.You're going to replace the BTUs lost at some point. (if you don't, you'll be cold). The longer you go in between cycles, the more ooomph you need to "catch back up". This means running water temps higher than needed, which has a fairly direct impact on efficiency. It also means that while you are not heating, the floor is cooling down, then heating back up again when it calls for heat. Again, mass can even that out a bit, and depending on your home and/or thermostat selection, it can even it out a lot. Or, it might just have wider swings and more discomfort.. it depends.However, if you can provide true modulated output to replace BTUs lost AS THEY ARE LOST, you never have to play "catch up".. you just replace what is lost, when it is lost, with a much lower output and lower water temperature. You can either do this with a modulating heat source (one that can modulate water temperature, not just output), or with mixing/reset controls, though a modulating heat source is by far the best choice. The takagi "modulates" its output to a setpoint, but doesn't modulate water temperature. So in that respect, it would be better than a poorly controlled conventional boiler (though one with reset controls and that is properly sized would beat the takagi), but if you're doing gas, heating a whole house with anything other than a modulating/condensing boiler really makes no sense these days, if you have a low temp system.. I've run the numbers. Payback is fairly short for all but the smallest loads. And you get a much more consistent and comfortable operation out of the deal as well. And none of this open system nonsense!-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
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Well, the discussion is certainly interesting!
Are you saying "steady ON" similer to how the Taco mixing block works? Just wondering..
That's the basic idea, yes. It uses "outdoor reset" to modulate the radiant water temperature to something closer to what you actually need at any particular time, rather than leaving it set to the hottest temp you'll need (or in one of the parent poster's cases, a point a bit below that and then manually adjusting your water temperature later).That poster is doing 'outdoor reset' of a very limited degree; they are running at 110, then turning it up when it gets really cold.That makes sense. What makes even more sense is to have the system constantly doing that math and adjusting itself on an ongoing basis.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Yes! We have no outside reset. The temp does not actually need to be raised when realy cold but I do it so that the run time is shorter. The next home will have more bells and whistles but I find that the less complication the less problems.
Thanks Rob, While I have faith in the system that was installed there is a little voodoo in it to me and I'm learning more about it as I move into the house while understanding the full system and it's inner workings. (It's a System 2000, LP fired, Boiler Mate indirect DHW, RFH and BB. AC in ductwork ) I'm not a total dummy in the HVAC dept. I live in 3500 feet, I personally manage 1 @ 24,000, 2@ 12,000, and 2 @ about 3000 sq. ft. all for one family. We design with the KISS attitude and the most complex is the 24K home.
With you being in Maine (we built up at Moosehead) I wish I found this site, and you a little sooner than when I did.
I must be the "customer" you would hate. We have an open system. It works for us but I am not saying it is the way to go. It has many concerns that a hands on homeowner has to deal with.
Our Takagi does regulate the temp of the water. I can read the temp going in to the the heater and the temp coming out. Therefore I can decide the temp going into the floor. We use 110 for most of the time.
I am soaking up all you say, because I am about to build a new bigger home. All the info you have to offer helps me in my new choices. I am likely going back to a Takagi or similar. The decsion is not final!
We are going to be heating our water mostly with a solar system and the water heater will only be for extra need in winter. If done right it's use should be minimal. What would you do in this situation? What kind of boiler?
I also can not go back to a system that runs out of hot water. I love my long hot showers. It is also a balance of up front costs, running costs and sytem size. Our house size would not warrant the cost of a boiler.( unless they have new smaller ones that are way cheaper. Again this is what works for us! I would not put a Takagi in a 4000 sq foot house. The efficency is lost(or at least I beleive so
I don't hate any customer, but if you were mine this would not be the system you have, because I wouldn't design an open system ;) I've seen too many kill themselves in short order. Never mind the health risks.Most homes I work on are around 2k square feet. Many are very well insulated. My average load is probably about 35-40kBTUs/hr under design conditions, in a relatively cold climate (lots of degree days). Oddly it's even higher loads in more mild climates, but mostly because the houses are much larger (that midatlantic region is hopping!). And not as well built.If you're in a climate with real winters, and your design load is over 30kBTUs/hr, make the budget fit. The mod/con boiler will pay for itself. This assumes a nice low temp system to work with.If you're using it only as backup, honestly I know a lot of people using mod/con boilers for backup.. and it does lend elegance and simplicity to the system, but frankly I don't see the point in caring about a backup source efficiency, PROVIDED IT IS REALLY BACKUP and not "second stage primary" heat. The less it's used the less it matters what you use.As for your other post, yes, you run 110 because you don't need it hotter most of the time. In fact, most of the time you don't need 110 either. However there is a limit to how much you want to play with the takagi, and frankly, trying to run the takagi at a water temperature close to what you need is not a very good idea as it will most likely short cycle itself. Your "burst effect" heating is probably the best way to run a takagi.But it's not the best way to run a heating system, that's all.
-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
May I ask what part of the continent you live in?
We are in western Wyoming but I am a transplanted B.C. girl.
May I also ask how big your house is? Ours is 1800 sq. ft. plus basement. 3200 sq. ft. total. Basement is Pressure treated wood foundation. We have 2x6 walls with 1.5" styrofoam added on exterior(R25). R40 insulation in roof and R50 beneath the living room floor which is suspended. i.e cold air below it.
We too will have an open system.
Just want to make sure I'm not getting into too much trouble! Also, have you had issues with the exchanger clogging up? I've also heard there may be problems with vent icing up in extreme cold temps -have you had any such issues?It's good to hear all points of view
Thanks, I appreciate your input!
Here's a nice thread with some discussion on tankless water heaters for you:http://radnet.groupee.net/eve/forums/a/tpc/f/4771065301/m/5071071481Whatever you do, please do not do an open system. A closed system is a one shot insurance policy for you, your home, and your heating system. There aren't many one time insurance policy payments out there, and this one you should take advantage of.At the very least use barrier pex so when you see my true ultimate wisdom, you can switch later and you haven't boxed yourself into anything. You can get such pex at reasonable prices.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Hi Rob,
Is there any reason why we couldn't switch to a closed system later if we find we're having trouble? I.e split the DHW off to a separate heater and use glycol for the floors?
Thanks,
Puzzle
If you use barrier pipe, your options are open. no pun intended.Non-barrier pipe means you may be in a situation that will promote premature breakdown of the inhibitors in glycol, which can result in excessively acidic pH levels and damage to your heating system. That stuff doesn't like oxygen either.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
I don't have barrier tubing- I believe I have heard that there is a chemical that can be added to help with this?
Hmm. You can add corrosion inhibitors to protect the ferrous components in the system (if any). But I am not sure about how to protect glycol's inhibitors from oxygen.Not saying you can't, I've just never looked into that. Maybe a call to Dow or something would be a good idea.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Does the glycol last forever (relatively) or does it need to be replaced or refreshed periodically?
My head hurts! Too much to think about here- but very interesting!
glycol needs to be checked every year or two in any system.In an open system, I would definitely check it every year. The question is how often you'll have to replace it, a messy and fairly expensive procedure. I'm not sure what is guaranteed in a closed system, but whatever it is, it's certain to be longer than in an open system, possibly much, much longer.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
1200 sq feet over a crawl space. Structural Insulated panel walls and roof. R28 and R40 We just insulated the floor( time is our enemy) Suspended cement(on plywood deck)
No problems with the exchanger freezing. It is inside. We have 3 -4 weeks of around 30 below. We have 2 zones. Living area and bedrooms. The bedroom zone almost never comes on because we like it cool(64-65) We get alot of sun in the winter and that keeps the temp up during the day. The living area has big south facing windows.
If you do go with an open system you have to plumb in such a way that you move the water through there on a regular basis. You don't want it standing over the summer or even very long in the winter. It is a precaution but every couple of weeks I will run the water through the floor when I am showering so as to move out stale water. I run the cold water through the floor in the summer before it hits the heater. That way I am constantly moving water so I never take a chance. I have had the heat off for three days in the winter while gone and it only went down to 55-60. I have a propane stove that is" in case". We have used it maybe 4 times in the winter. We use it mostly in the spring or fall for quick heat without heating the floor.(Maybe 3 or 4 times in a season).
An open system means no antifreeze and the possibility of freezing. You must have a back-up plan if you go that way.
You need a water softner! Scale is your enemy! One of the downfalls of the Takagi. They have systems to run a solution that will clean them.
Are you heating the whole house with radiant? including the basement?
Where are you in Canada?
Edmonton, Alberta.
Guess I'll check out water softeners. Thanks for the heads up!
Certainly plenty to think about here...
Whoops, sorry. Yes, we are heating the entire house with .
I don't want to be a downer but with that size of home to heat, you should price out and investigate a boiler as well. My house is small. The heater does not need to run alot. Your house might require more run time.
My next house will be at least that big and I will be looking at all the options. Also that much water running through an open system , you will have more buildup(hard water) and debris problem.
The bigger the system, the more complex your needs. Mine is small and simple to handle. I can not say that I will do the same with a bigger system.
"tall ceilings and lots of windows especially on the North side"
Hopefully you have some really good insulating strategies for all those North-side windows. I doubt I'm telling you anything new, but typical energy-efficient homes try to minimize north side windows - especially where it gets to 40 below!
Yes I know. But the lay of the land commanded! We did debate this long and hard...
That said, the windows throughout are triple glazed and we have 2X 6 walls to which we are also adding 1 1/2" of styrofoam to the exterior.
Thanks for the input.
Puzzle