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Low temperature staple up radiant heating

hotpauliehotpaulie Posts: 1Member
I’m evaluating a possible staple up radiant heating job.
The house burns a lot of propane and the owner wants to stop spending as much as his mortgage on heating the house in winter. Insulation and air sealing land are in the works but beyond making the house more efficient, I’d like to make it less dependent on such an expensive fuel Source.
Air to air heat pumps have been explored and they will probably be what I go with on this job but I’m curious about another.
An air to water heat pump.
Expensive but really cool.
The model i was after puts out 120degf water until 14degf then it derates until minus 5 when it shuts off.
My average low temperature in my coldest month last year and before was around 17 but we frequently get days and sometiese a week we’re we are below 14f. At that point I could still use the heat pump and it would be vastly more economical than propane. I could supplement it with electric auxiliary heat but that is only slightly cheaper per btu.

My question is: can I run a lower water loop temperature (say 105 degf) if I run more tubing closer together in the floor joists?
Pex can theoretically be bent to a radius of 6 times it’s diameter so I could theoretically install 6” on center and fit 3 runs into a typical joist bay.
Has anyone ever tried running loqer than 120degf temps in radiant staple up jobs?
Does the closer spacing even translate to lower temps?
There’s a shag carpet in the loving room which will be eventually replaced with hardwood. Linoleum in the kitchen which will eventually be replaced with tile or hardwood and then typical carpet in the bedroom.

Comments

  • hot_rodhot_rod Posts: 11,749Member
    Just know that the operating cost is directly tied to the building efficiency. The type of heat emitter really cannot change a high load building. I'd spend dollars on the tighten up first.

    A more efficient boiler, and modulation can reduce some fuel cost, properly applied, but it will take the exact amount of BTU/hr to heat regardless of the "system"

    And there are some high load buildings where radiant floors alone will not cover the load, regardless of tube spacing and SWT. I'm comfortable with mid 20's BTU/ sq. ft output from comfortable radiant floors. if you load calc shows larger btu requirements....

    A room by room load calc would answer all your questions, How large is the load, how to reduce it, and what type of emitters and SWT can you work within.

    Loose the shag insulation/ carpet, it too has R value working against heat transfer f you go with radiant floor applications.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • KathieKathie Posts: 2Member
    Does that mean you can not use an area rug, over laminate?
  • hot_rodhot_rod Posts: 11,749Member
    Any floor covering you put over a radiant floor will reduce the output. Usually you can accommodate an area rug. Thin with no pad if possible.

    1/2" carpet and pad, consider that R-1.4, multiply by 1.5 if it's wool carpet, according to the RPA RadPad calculator.

    It comes down to the heat load and design. If the floor without any coverings just meets the load on design days, any coverings or objects that block the energy will change the heating output, and could possibly leave you in the cold :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • ZmanZman Posts: 5,044Member
    hotpaulie said:

    I’m evaluating a possible staple up radiant heating job.

    The house burns a lot of propane and the owner wants to stop spending as much as his mortgage on heating the house in winter. Insulation and air sealing land are in the works but beyond making the house more efficient, I’d like to make it less dependent on such an expensive fuel Source.

    Air to air heat pumps have been explored and they will probably be what I go with on this job but I’m curious about another.

    An air to water heat pump.

    Expensive but really cool.

    The model i was after puts out 120degf water until 14degf then it derates until minus 5 when it shuts off.

    My average low temperature in my coldest month last year and before was around 17 but we frequently get days and sometiese a week we’re we are below 14f. At that point I could still use the heat pump and it would be vastly more economical than propane. I could supplement it with electric auxiliary heat but that is only slightly cheaper per btu.



    My question is: can I run a lower water loop temperature (say 105 degf) if I run more tubing closer together in the floor joists?

    Pex can theoretically be bent to a radius of 6 times it’s diameter so I could theoretically install 6” on center and fit 3 runs into a typical joist bay.

    Has anyone ever tried running loqer than 120degf temps in radiant staple up jobs?

    Does the closer spacing even translate to lower temps?

    There’s a shag carpet in the loving room which will be eventually replaced with hardwood. Linoleum in the kitchen which will eventually be replaced with tile or hardwood and then typical carpet in the bedroom.

    If you go radiant, particularly if air to water heat pumps are in the mix, you want to design for the lowest water temp possible. For under floor installations, that will mean using transfer plates. You will be better off with 2 loops per 14.5" bay with plates rather than 3 loops without plates. Improving the building envelope will also help reduce temps greatly.

    Keep in mind that, with outdoor reset, you only need the highest temp on your design day. You may end up with a system that requires 130 on design day but will run at 105 on the average day. Your heat pump might run at a COP of 1 on the design day and still end up running an average of COP 3
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • ZmanZman Posts: 5,044Member
    Kathie said:

    Does that mean you can not use an area rug, over laminate?

    @Kathie
    Some of these conversations are fairly nerdy discussions about squeezing that last few percentages of efficiency out of a system. Floor coverings have insulating properties that will require slightly higher water temps which will use a little more fuel.

    Yes, you can use floor covering with radiant.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • pecmsgpecmsg Posts: 844Member
    If they want to save energy Tighten the envelope!

    Low temperature radiant, high temperature rads, Steam ALL cost money as it leaks out at the same rate. A btu is a BTU!
  • hot_rodhot_rod Posts: 11,749Member
    Most of the radiant design software programs include an "assumption" report.

    Basically assuring the radiant design will heat the home or existing building as it was presented.

    If anything in the building changes from the original plan, the system may not perform as designed, agree and sign by the X :).

    Insulation changes, window changes, poor construction workmanship, and yes a change of floor covering can and will effect the final outcome.

    There are easy number crunching step to assure you do not risk having an under performing, or uncomfortable radiant system, may as well use them.

    I have been in radiantly heated homes that have small portable space heaters stashed in rooms to cover under-performing designs, some where slab homes that were later carpeted and padded.
    There is a safe limit to how much you can "crank" SWT. The floor covering folks are clear about tha

    Bare slabs have a temperature limit to maintain comfort to bare feet, 80- 82°F is a common range. Cranking SWT to overcome some carpeted areas may cause the bare slab areas to be too hot to the foot.

    Include any mix of floor coverings in the original design, would be wise advise.

    Pros on this list can offer design help is you do not want to tackle this yourself. Expect to pay for a professional, guaranteed design specific to your project.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • ZmanZman Posts: 5,044Member
    pecmsg said:

    If they want to save energy Tighten the envelope!

    Low temperature radiant, high temperature rads, Steam ALL cost money as it leaks out at the same rate. A btu is a BTU!

    This is true, however...

    Air to Water heat pumps which extract heat from the outdoors and use it for to heat the building perform much better at low water temps. Condensing boilers run more efficiently at low temps. Hot water solar panels perform mush better at low temps.

    Both building envelope and emitter design are critical to maximizing efficiency. The better the envelope the lower the heating requirements, the lower the water temps, the higher the efficiency. You can't look at just one part of this if you are seeking a super efficient home.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • kenjohnsonkenjohnson Posts: 34Member
    Having just designed and installed my own underfloor radiant heating system with a geothermal heat pump (and received a great deal of help from here in doing so), I can offer the following advice.

    1. It is a lot of work to design the loop system and run the loops. I was able to do both. If you have to pay someone to do it, they will charge a lot. It's an awesome system when it is finished with a great, even heat, but not everyone will want to pay for the time and trouble.
    2. If you are not going to use a high quality, thick aluminum plate on the PEX tubes, it will not work with low temperature water (less than 120 degree F water temperature).
    3. If you use aluminum plates, you will hate to grind off every nail that protrudes where the plates will go. This takes a lot of time and is dirty, messy work.
    4. Two pex pipes per bay is optimal. Three only gives you about 10% more heat output and makes the loop design vastly more complex and difficult to implement. It's not worth it to do three - just run slightly higher water temperatures. I did three loops in a couple of areas and wished during that install that I hadn't.
    5. I tightened my house up a lot and insulated it very well - about as well as you can doing a conventional renovation. I will still need 120 degree water or so at 0 degrees F outdoor temperature. If I could only supply 105 degree F water, it would still meet about half my heating needs.

    I'm glad that I installed what I did. I also understand why most wouldn't want to pay for the labor and materials to get it. I think for most people, especially those who say "I'd like to save some money on my heating system", the best bang-for-the-buck is a air-to-air mini split ductless heat pump or two, maybe even one that runs very efficiently well below 5 degrees F.
  • hot_rodhot_rod Posts: 11,749Member

    Having just designed and installed my own underfloor radiant heating system with a geothermal heat pump (and received a great deal of help from here in doing so), I can offer the following advice.

    1. It is a lot of work to design the loop system and run the loops. I was able to do both. If you have to pay someone to do it, they will charge a lot. It's an awesome system when it is finished with a great, even heat, but not everyone will want to pay for the time and trouble.
    2. If you are not going to use a high quality, thick aluminum plate on the PEX tubes, it will not work with low temperature water (less than 120 degree F water temperature).
    3. If you use aluminum plates, you will hate to grind off every nail that protrudes where the plates will go. This takes a lot of time and is dirty, messy work.
    4. Two pex pipes per bay is optimal. Three only gives you about 10% more heat output and makes the loop design vastly more complex and difficult to implement. It's not worth it to do three - just run slightly higher water temperatures. I did three loops in a couple of areas and wished during that install that I hadn't.
    5. I tightened my house up a lot and insulated it very well - about as well as you can doing a conventional renovation. I will still need 120 degree water or so at 0 degrees F outdoor temperature. If I could only supply 105 degree F water, it would still meet about half my heating needs.

    I'm glad that I installed what I did. I also understand why most wouldn't want to pay for the labor and materials to get it. I think for most people, especially those who say "I'd like to save some money on my heating system", the best bang-for-the-buck is a air-to-air mini split ductless heat pump or two, maybe even one that runs very efficiently well below 5 degrees F.

    Tell us more about the design & installation. What was the btu/sq. ft load on the rooms, or the highest load area?

    Floor covering and subfloor R-value?

    I'd like to see how closely our number crunching matches real world installation performance data.

    Simulation-wise a 120°SWT, 115° AWT should get you around a 15 btu/ sq. ft.hr. output from an R-1 floor panel. I would guess in a "tightened" structure that may be adequate.

    I'd also suggest most, maybe all heat load calc have some "fudge factor" in them. Do any heat load calcs take into account internal gains? None that I have tried.

    So the calculated load may have a 5-10% safety factor? Throw some internal gains, as all homes have "stuff" inside turning electricity into thermal energy, maybe load calcs are 15% + on the high side?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • kenjohnsonkenjohnson Posts: 34Member
    Each calculation was room-by-room taking account specific square footage and R-value of windows, headers, framing, and wall/floor/ceiling cavities, all calculated in Excel. There was no fudge factor used - I ran the same basic data through several other calculators and the results were so much higher as to be unusable. I assumed infiltration was negligible (first blower door test was 1.4 ACH50, and I've tightened it up a bit more since then). I assumed internal gains of about 1500 BTU/hour, but also assumed infiltration losses would negate those gains. I assumed no solar gain (a good assumption in Central NY winters).

    A typical floor is about R-2, with some averaging higher due to presence of floor rugs. Net effective radiated heat is about 15 to 17 BTU/square foot (would have to boot up my other computer to know for sure) at 0 degree F outdoor temperature.

    I'll have some better, though still not final, performance data this winter after I finish all of the joist insulation under the plates/tubes and the storm windows installed. The winter after the house will be occupied and I'll have final data (I will post it).

    But with the ODR settings last year, water temperature was 123 degrees F at 0 degrees F outdoor, and the house was able to warm up from 63 to 70 degrees in about 7 hours with the circulator running constantly on a cloudy day. So it's pretty much working as modeled. I've tweaked the ODR to run at lower temperatures, so we'll see if it keeps up as designed with below 0 degree outdoor temperatures.
  • hot_rodhot_rod Posts: 11,749Member
    Usually when Siggy runs simulations for our examples he uses Syracuse, NY as a weather station close to his climate. Here is some BIN data for that area.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • kenjohnsonkenjohnson Posts: 34Member
    Syracuse is a good 5-7 degrees warmer than where I am at.
    Regardless, system is up and running, as designed. Works great, thanks to the great advice I got here. I'd highly recommend this approach if you don't mind spending the money and/or the time to do it right.
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