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Radiant Aluminum Plates pay back?

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If you plate the bathroom, but not the adjacent room, I bet you'd find the bathrooms will run much warmer without the additional zone.

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  • Granite Stater
    Granite Stater Member Posts: 11
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    Radiant heat with or without plates? Payback?

    Has anyone ever figured out the payback on installing aluminum plates in a radiant floor heating system? I realize that the plates will transfer heat alot quicker than a suspended (pex clipped up) radiant system. I am building 2500 sq ft two story house and to add the plates could be an extra $10,000 dollars. The heat loss does not call for plates. The professional plumber that is installing my system has a theory that makes sense to me, The plates will heat the floor quicker but the return water temp is going to be alot lower, so the bolier is going to run just as long if not longer. With the suspended radiant the return temp is going to be closer to the out going temp because the plates are not sucking the heat out of the tubing as fast. Please give me your theory on this. Another question is my upstairs is going to be on six different zones, should I put up an insulated blocker in the celings so that the heat wil not travel down the bay(floor joist) into the other zones? I know that heat will rise, but I do not see how it will not radiant to the other zones that are at different temps. To me the heat is going to follow its path to the coldest point. All of your help will be greatly appreciated. This house is being built in New Hampshire.
  • [Deleted User]
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    Your plumber is mistaken...

    He's also not paying your monthly gas bills, so why should he care?

    Can the installation be done without plates? Well, if you ran the numbers, and it says you can, then you should be able to. But, and thats a BIG butt, when your wife throws down the rugs she wants, you now have a lower output, and you have little to no wiggle room to play with. You can't "turn it up", because you will probably be running at the max recommended temps any way. With plates, which utilize conduction for heat transfer, which IS the KING of heat transfer, you have LOTS of wiggle room if needed.

    For me, and my money, I'd go with the extruded plates and a modulating/condensing heat source. If WarmBoard were feasible, that would be my intial preference, but it sounds as if its too late for that right now. The initial cost increase will reduce your gas bills by a significant amount, but if you go plateless, you'll never know...

    There is no right way to do anything wrong.

    As for joist dams, absolutely.

    It's your money, spend it wisely. The first time.

    ME
  • Uni R_3
    Uni R_3 Member Posts: 299
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    Formulae

    The numbers are fairly simple. For a present value of $10,000 divide in the estimated annual savings. The savings is the estimated annual bill times the expected efficiency hit from running higher temps. With ODR, your temp will probably only be high about a dozen winter days. That hit shouldn't be too big. Plus some type of opportunity cost should be factored in - you could have invested that $10K instead. Given all that, you just might find yourself looking at an impossible 100 year payback.

    The payback won't be very impressive most likely depending on what numbers you use, but you really must think forward. We're the generation that has seen energy consumption outstrip long term sustainable energy supply levels of known resource technologies.

    So think green both ways - that payback will come way down every time the energy resources all ratchet up and they will as the world places higher and higher demand on energy equality. Don't think all this new demand from China and India aren't going to drive up world energy costs!

    A rough way to get your estimated annual fuel bill would be 5 x annual heating degree days (can be found online for a city near you) x square footage of livable space. Divide that per 100,000 to get it to therms and multiply by the rate per therm. That should give you a rough upper end depending on quality of insulation, if you're top of a mountain etc.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    For new construction consider Warmboard It's a structural floor with a continuous layer of fairly heavy aluminum on top. Quite cost effective in new construction. Google the cost and compare to $10,000 added for plates while subtracting the sub-floor...

    If you truly must have six different zones just in the upstairs of a 2,500 s.f. home, consider FHVs (floor heat valves). I won't mention specific costs but certainly comparable to a decent thermostat and a zone circulator/valve.

    As to suspened vx. plates/Warmboard I have to agree with previous posts--your plumber isn't paying the heat bills... Bare tube (suspended or "staple-up") systems in your area of the country are often considered "constipated"--they can't put out anywhere near what's going in unless you utterly force it out via HIGH temperature.

  • ALH_4
    ALH_4 Member Posts: 1,790
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    Plates

    Plates might not pay for themselves in cash savings. However, they greatly increase the output and thermal performance of the radiant floor. At times, the difference between plates and no plates is the difference between needing supplemental heat or not. Some of the manufacturers' output ratings for staple-up and suspended tube are very optimistic.

    There is a difference between temperature and heat. The suspended tube must be hotter to create convection in the joist bay, while the pex in plates can have a much lower supply temperature and deliver the same amount of heat. Air is a good insulator.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
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    Not a good physics student

    Very interesting theory your plumber had, but he must not have paid attention in physics class. Here's the deal in simple terms.

    His theory was - "the plates will heat the floor quicker but the return water temp is going to be alot lower, so the bolier is going to run just as long if not longer."

    Got that one half right.

    A gallon of water, based on its temperature and mass, flowing through a pipe, has a certain amount of heat energy associated with it. As it moves along the pex, it gives off it's heat energy to everything it comes in contact with. Air, not being very dense, and having little mass, does not absorb very much heat energy. Thats why we use the "transfer plates" - to extract the heat from the pex, by means of conduction, to heat your floor.

    As this happens, the temperature of the water in the pipe drops accordingly. The heat energy is being transferred, from the pex, into the room above, and eventually satisfies the thermostat which then turns off the boiler and pump.

    Now lets look at the suspended pex in the joist bay. Your plumber's theory was - " with the suspended radiant the return temp is going to be closer to the out going temp because the plates are not sucking the heat out of the tubing as fast".

    Well he's right about that. The difference between the supply and return temperatures will be alot closer. But what does that really mean? It indicates there is less transfer of heat energy taking place. Your thermostat is still in the room above asking for heat. So the boiler / circulator keep running longer, trying to answer the call. This is not efficient situation. It typcially will cause your boiler to cycle more. The boiler is staying on longer, - it can't get rid of the heat energy it's making, and goes off on high limit. Keep in mind, that everytime the boiler is firing, approx 18% - 20% of your fuel dollar is going right out the chimney (assuming you have a conventional boiler).

    You indicate your in New Hampshire. Your outdoor design temps must be close to 0F or lower. Like Mark said, a few throw rugs and you can be in big trouble. I agree, if you are trying to do a radiant home, a condensing boiler would be a smart choice which would have a substantial payback.

    Just one more point, - $10,000 to add the plates to a system of pex tubes under the floor in a 2500 sqft home ?? or is tht the price of the entire radiant heat option? If thats the additional charge to install the plates, I would suggest looking for a few more quotes.

    Good luck on your project. Keep learning - keep asking questions - it will help you make better choices.
  • Plumdog_2
    Plumdog_2 Member Posts: 873
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    my 2 cents

    use an above-the-subfloor install and you will be happier.
    A lightwieght overpour works great. (if it ain't already framed)
  • hot_rod
    hot_rod Member Posts: 22,158
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    Depends on the heat load numbers

    I'm starting to see BTU/sq. ft. numbers fall into the low teens and below, more and more often..

    ICF and SIP homes without excessive glass can easily hit those numbers. Plateless can make below 15 BTU/ sq. ft numbers fairly easily.

    Actually for bedrooms and sleeping areas I feel panel rads with TRVs make a lot more sense. Quicker recovery, not effected by furniture and floor coverings, and probably less $$'s.

    Not a lot of benefit from warm bedroom floors when mujch of it is under furnishings, and little time is spent standing in bedrooms.

    Invest radiant in the most used, cool surfaced rooms first. Baths and kitchens as well as gathering rooms are a must in my opinion.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Troy_3
    Troy_3 Member Posts: 479
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    Comfort=What value

    How much do you value comfort. Will it bother you if you can only reach 60deg. on the coldest days of the year? That may only be 10 days. If that is not acceptable then it isn't a factor of payback. Suspended tubes in your area is marginal at best. I tend to figure this is a system that will be required to heat this structure for the next 100 years. Don't scimp. Do it right or blow air! That's my motto. I agree that plates for 2500 sq. feet should not add $10,000.
  • jp_2
    jp_2 Member Posts: 1,935
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    pay now or pay later

    one answer is fairly simple.

    suspended systems require high water tempertures to heat the rooms. now think about this, which require more heat, keeping a pot of water on the stove at 100F or 150F?
  • Ruthe Jubinville_2
    Ruthe Jubinville_2 Member Posts: 674
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    radiant no matter what way

    I wouldn't have anything but radiant in a new home. Jerry put it in out 120 year old house in the kitchen, bath and part of the bedroom. Love the warm floors in bedroom and bath when you step out of bed. All are suspended and some under carpet. He always had to try out something for himself before he would sellit. .They are the warmest rooms in my house on the coldest days. Don't need the temp as high in the rooms with radiant. and I am in New England ..
    .. Ruthe
  • plates

    we have done well over 100 houses in new hampshire with radiant heat.all the heat losses are figured with -20 degrees.we use wirsbo heat loss program to figure the heat loss.Yes i agree that the plates transfer the heat better than suspened pipe.but in a cases where the heat loss dosn't reguire plates we don't install them.where the heatloss says we need them we install them.jobs done with out plates we have never had a complaint of to high of heat bills nor room not heating.in this case a 2500 sg ft house would reguire about 1100 plates at $8.00 a plate plus extra labor to install.so if this $10,000 dollar price is correct how much would you save 10% -15% if your heating bill is $2,200 a year thats a long pay back.We did a house that was 6,000 sg feet just the bathrooms plated in the house.Customer was talking while playing golf with a heating contractor and the other contractor said he would have never done the job with out plating it.So HO asked me why we didn't use plates for his house,I asked does heat heat on the coldest days up on the hill.He said heats great.Asked how much he spent to heat his house that winter,he said it was $3,000 dollars which he thoght was great.I explained to him that the heat loss didn't reguire plates and if we installed them it would be about 15,000 dollars extra if not more and if it saved you 20% on your heating cost it would take you a least 20 yrs to pay for it and if you had to pay an extra 15,000 dollars to install this heating system would you have done it-he said no.So i guess my point is yes install plates when it calls for them if you don't really need them give the customer the option if he would like to install them for the extra money.I am going by just my experence thats about all we do is radiant and every customer has heard about us from other customers we have installed for.I would dare say 100% satisfied customers plated and suspended pipe.
  • ALH_4
    ALH_4 Member Posts: 1,790
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    Hybrid Systems

    I agree, "hybrid" radiator/radiant systems are a very nice compromise.

    Radiant makes sense in kitchens where there is no place to put a radiator. Radiant also makes sense in bathrooms where people are not clothed and cold surfaces are uncomfortable. If the radiant is confined to these areas, adding plates is not a huge expense and it has performance advantages.

    TRV'ed radiators work great everywhere else.

    Constant circulation is necessary for these systems to function their best.

    Yes, I used TRV as a verb...

    The point is that plates are mostly about comfort and heating performance, and system efficiency. Not ironically, those happen to be three of the primary reasons people choose radiant heating.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
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    Plates under new bathrooms ?

    If I understood your post correctly, you would rather use plates in a bathroom than install the pex directly in the mud? I suppose that the mud install would require a much lower temp, hence another tempering valve and circ.




  • plates in bathroom

    we plated the bathrooms because the heat loss caller for them.we always but the bathrooms on seperate zones because most people want their bedrooms colder than their baths.as far as in the mud their was a floor height issue.
  • ALH_4
    ALH_4 Member Posts: 1,790
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    plates

    It seems to simplify the construction process, and makes the tile guys happier if the installation is below floor plates instead of tube directly beneath their tile. If the rest of the system is radiators and the bathroom is radiant floor, floor elevations can be an issue with an above-the-floor installation. Temperatures for Thermofin are nearly the same as for concrete pours.
  • Radiant Wizard
    Radiant Wizard Member Posts: 159
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    With without Plates

    > Has anyone ever figured out the payback on

    > installing aluminum plates in a radiant floor

    > heating system? I realize that the plates will

    > transfer heat alot quicker than a suspended (pex

    > clipped up) radiant system. I am building 2500

    > sq ft two story house and to add the plates could

    > be an extra $10,000 dollars. The heat loss does

    > not call for plates. The professional plumber

    > that is installing my system has a theory that

    > makes sense to me, The plates will heat the floor

    > quicker but the return water temp is going to be

    > alot lower, so the bolier is going to run just as

    > long if not longer. With the suspended radiant

    > the return temp is going to be closer to the out

    > going temp because the plates are not sucking the

    > heat out of the tubing as fast. Please give me

    > your theory on this. Another question is my

    > upstairs is going to be on six different zones,

    > should I put up an insulated blocker in the

    > celings so that the heat wil not travel down the

    > bay(floor joist) into the other zones? I know

    > that heat will rise, but I do not see how it will

    > not radiant to the other zones that are at

    > different temps. To me the heat is going to

    > follow its path to the coldest point. All of

    > your help will be greatly appreciated. This

    > house is being built in New Hampshire.



    First off to anwser the question I have to aske a question. While the plates are one factor, how is the radiant system controlled. Are we doing fixed temp (ie, Thermostatic Mixing Valve) or Modulating temp (ie, injection or motorized mixing valve). While your contractors theroy sounds nice a good radiant installer/designer is going to design the system with a 15 to 20 degree delta T (difference in the temp going into the floor and the temp returning to the boiler) so that there squashes his thought.

    Here in my opion are the factors of why we use plates.

    1. Lower water temp equals efficient system. Remember for every 3 degrees we can run a system below 180 degrees we can save roughly 1 percent.

    2. Response time. The floor will come up to temp quicker with plates. Why does this matter...Look at the home. Is solar gain an issue. The last thing we want is Mr. Heat Tab (the Sun) to satisfy a room and then when he ducks at about 4 in the afternoon we have to try to get a stone cold floor to satisified. We never want to chase a set point.

    3. You pay for what you get and over and over I've seen regret.
  • Granite Stater
    Granite Stater Member Posts: 11
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    Anyone have any comments on Bryant's post dated 4/25/07

    Please comment on Bryants posting dated 4/25/07. What he is talking about seems to be very close to the way that my plumber described it to me. If the heat loss does not call for plates, then why put them in! Thank you all for your comments.
  • ALH_4
    ALH_4 Member Posts: 1,790
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    Plates again

    Plates increase the potential output of the floor, decrease the response time, and lower the required fluid temperature to provide the same output whem compared to suspended tube. Radiant is very forgiving. There are thousands of homes that heat just fine with convective radiant floors. If your heat loss calculation says you don't need them, then it's up to you to pick the fluid temperature you would like to use to heat your home. I strongly urge you to use a constant circulation control strategy.


  • Depends on what that means, doesn't it?

    Does that mean 180 degree water will heat the house? Or does that mean it'll do the job at 120?

    Are you using a condensing boiler? could you? would it save you the chimney too?

    Any risk of rug usage, higher than expected heat loads, high wind loads, etc?

    Personally, I am not an advocate of high temperature heating, for the simple fact that only limited heat sources can generate high temperature water, and I think future flexibility is important. Practically anything that heats can generate 100-110 degree water. Not so for 180.

    That said, a suspended tube/baseboard combo system can easily be used to run lower temps. suspended tube/ceiling combo systems can do the same, and both options eliminate floor covering concerns.

    When loads are very low, then suspended tube can be fine too.

    If running area A with good plates results in a water temperature that area B can use without plates to meet it's load, so be it; zone separately, and go crazy!

    Lots of options. But jacking a joist temperature up dozens of degrees doesn't seem particularly efficient. You'd expect to pay more to heat a room to 90, right? Well, what about your joist cavities jumping from 100 to 150? This could be a big consideration if you're over cold space especially.
  • how about a combo meal?

    I'm currently in the design phase with a heating contractor that is having a new house built. He is balking at the extra expense of the plates, and I can understand that. In this case, the area in question is $2132 cheaper in material using PEX clips in place of Joist Trak plates. The max water temp was 152F with clips, 109F with plates.

    I took a look at the design and found two rooms that were driving the max temp up, so I put plates back in the design for those rooms, which drove the max temp down to 128F, ending up being $1100 cheaper than full plates. I think its a good compromise between intial first cost and lifetime operating costs.

    I would have preferred to use the design with full plates as I feel it would be more efficient. However, I can't estimate the savings accurately. That frustrates me.

    Best regards, Pat
  • [Deleted User]
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    Super insulated homes...

    with heat load requirements at less than 15 btu's per square foot per hour probably would work OK. But then theres the noise issues. In the homes that I've worked on with staple up PEX with O2 barrier, when the zone first turns on, it sounds like a herd of crickets running through the floor. TICK TICK TICK tick tick tick tick tick, and the homeowners are NOT happy with the results. Use of the cheap flashing type of plates change that noise to the sound of an old oil can. BOOIIIiinnnng. Worse than the herd of crickets.

    My definition of pure comfort is not being aware of your surroundings. You are neither hot, nor cold, and you CAN"T HEAR YOUR SYSTEM. You are simply comfortable.

    Now, if all you're looking for is cheap heat, that is but one component of comfort, and it can be had with a 55 gallon drum placed near the middle of the room with a smoke pipe connected to it, and under worse case scenario, you can burn furniture, oak trim, old pets and mother in laws in it to keep warm:-)

    It's your money. Spend it wisely the first time to avoid having to spend it again...and suffer through discomfort in the process. And trust me on this, I work on a LOT of staple up systems with dissatisfied customers installed by other contractors. High utility bills, low comfort and noisy operation are the most common compalints. If your contractor can show you the math that says it will work, then the only unknown will be the noise and cost of operation.

    ME
  • jp_2
    jp_2 Member Posts: 1,935
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    IS heat loss Just heat loss?

    I would strongly question what is meant by "heats just fine"? compared to what?

    this is where I think a Btu is NOT a Btu.

    if a system can run at 95F compare to 150F and say there is just a 10% difference I have to disagree. true I have no real proof but I do know the higher your running temp the higher your energy losses and those losses are NOT linear.

    if you need to run temps 15% higher, thats more than 15% increase in energy.
  • ALH_4
    ALH_4 Member Posts: 1,790
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    Heat

    By "heat just fine" I meant that it will keep the room warm.

    I agree that the benefits of plates are more than they appear on the surface. Should we design systems just good enough to satisfy the thermostat? Is it wasteful to design them better than that? Is a satisfied thermostat also a satisfied occupant? That depends on whether that occupant is paying the fuel bill. ;-)

    I will never be a defender of suspended tube systems. However, it is possible to satisfy the thermostat with suspended tube if the heat loss is low enough. At what cost? That is difficult to determine quantitatively. I have never and will never design or install a suspended tube system because I believe the benefits of conductive methods outweigh the costs.


  • careful with absolutes andrew;

    in mild climates, you may not have enough time of heating to ever make this case, even if the PSF load is high (low degree day count).

    In any climate, the difference between installation methods in terms of temps and efficiency falls with the intensity of the load. Water temps between methods at 10 BTUs/sq ft, for example, are a lot closer than at 20 BTUs/sq ft.
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