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  1. #1
    Join Date
    Feb 2009
    Posts
    13

    Trying to Fine tune hydronic radiant.

    Greetings, Happy Holidays to all...

    Did a complete gut and remodel of my kitchen this summer and installed an underfloor hydronic system. Heating contractor did all the piping, from the furnace to the radiant distribution panel, controls, etc. I did the PEX staple up with metal heat transfer plates, and insulated the joist bays with 3.5" fiberglass.

    THis is the first winter and I am trying to tune in the system. Until this week, (outdoor temps in the 40's and 50's) the system heated room well. Winter then suddenly arrived in the northeast this week and I can't get much above 65 degrees (internal air temperature), with the outside temp in the high 20's to mid 30's. The flooring manufacturer (wood look laminate) recommends that the "surface" that the flooring is installed on is not above 90 degrees. When job completed in august the contractor set the floor temperature sensor for the radiant system at 90 degrees max. The floor construction is 3/4" red oak (original 125 year old planking), in various places building felt to level the surface, then 1/2" plywood subfloor, unison 2-1 foam underlayment and then the laminate. The sensor is on the bottom of this cross section, mounted in a 4"x4" area where the metal heat transfer surface was removed.

    Here is my question. Is there heat transfer loss through the floor cross section of 3/4 oak, 1/2 plywood and foam underlayment, OR does the whole floor eventually reach the same temp, i.e. in this case 90 degrees. The top side of the laminate is nowhere near 90 degrees, but obviously it's radiating the heat upwards. I'm sure you can see where I'm heading...can I nudge the slab sensor limit up a bit? I don't have any way to directly measure the temperature of the topside of the foam underlayment without pulling up the laminate. THANKS for all help.

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,315
    Get an inexpensive infrared thermometer gun and measure your floor temperature under various weather conditions. If during the coldest days you notice the floor temperature does not get as warm as during warmer weather (but where you still need heat), you may need some form of temperature reset for your hot water loop. Heat loss to the outdoors from your house increases as it gets colder outside, and if the water supplied to the radiant floor sections is always the same temperature, it may not keep you comfortable on the coldest days.

    From what you described, the floor sensor will not let the surface temp exceed 90 degrees, so if you're never even getting close to that point, your water loop temperature may be too cool.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #3
    Join Date
    Nov 2009
    Location
    Sacramento, CA
    Posts
    139
    +1 Could not have said it better Shophound

  4. #4
    Join Date
    Mar 2003
    Posts
    7,321
    most radiant systems are designed for no more than 68 degrees f indoor temp, thinking that with radiant all surfaces will be warm as opposed to scorched air. that being said, floor temp should be just a tad higher than skin temp(for obvious reasons). the whole floor is meant to be your heat source. as stated, you need to look at your actual floor temps. sensor location may not be perfect, and if so, raising the limit may just help. in addition, most radiant loops are designed with outdoor reset, so as temp drops outside, loop temp goes up to compensate. floor temp sensor may need to be replaced with a room sensor, since this is a low mass application, with loop temp limits remaining. are you doing constant circulation or powerheads?

  5. #5
    Join Date
    Feb 2009
    Posts
    13

    Reply

    Sorry guys...as the homeowner, Not sure about "powerheads", I can tell you the radiant circulator is NOT on all the time. I will look into the infrared gun. Could I get the same effect from using a surface thermometer and recording the floor temp under various conditions?

    I increased the floor limit from 90 to 95 degrees which raised the air temp in the room from 65-67, with an outside air temp of 35. Again, my concern at this stage was not increasing the floor temp too much for the laminate flooring. I am assuming that the top surface of my subfloor is not the same temp at the bottom of the subfloor where the pex and the sensor is.

  6. #6
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,315
    I'll let flange field the powerhead question.

    The IR gun lets you get a reading quickly, and you can move place to place quickly to see how evenly your floor is heated. It's also handy for other things, so it's not a "once and done" type of purchase.

    What I would want to know from the manufacturer of your laminate is which temperature is of concern to them. If it's surface temperature (which I suspect it is), your IR gun will be your best friend. If the sensor's ultimate purpose is to set a limit for surface temperature, yet senses from the subfloor, that's probably okay. You just set the limit so you never see surface temps near what is not recommended for it to be at.

    BTW, you did mention a two degree increase in room temperature. Was that enough to make you comfortable?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  7. #7
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,003
    Quote Originally Posted by tmy23 View Post
    Greetings, Happy Holidays to all...

    Did a complete gut and remodel of my kitchen this summer and installed an underfloor hydronic system. Heating contractor did all the piping, from the furnace to the radiant distribution panel, controls, etc. I did the PEX staple up with metal heat transfer plates, and insulated the joist bays with 3.5" fiberglass.

    Here is my question. Is there heat transfer loss through the floor cross section of 3/4 oak, 1/2 plywood and foam underlayment, OR does the whole floor eventually reach the same temp, i.e. in this case 90 degrees.
    Did anyone do a heat load calculation on the kitchen before the recommedations were made as to the design of the radiant system?

    Your "radiator" to heat the kitchen is your floor, well actually it's whatever square footage of exposed floor surface that has tubing under it. If the radiator isn't big enough in square footage to supply the required energy into the space to replace what is being lost you're not going to heat the space to the desired temperature.

    When you said you did the PEX staple up with metal heat trasfer plates what kind of plates? Are they fairly flexible aluminum, able to cut them with metal shears? Is there one run of PEX in each joist space or is there two per joist.

    Is the insulation in contact with the transfer plates or did you leave an air space? 3.5" is normally considered minimal when insulating beneath radiant.

    Yes to your question. Any material between the heat source (the tubing) and the area it's trying to deliver energy to will slow the transfer process down. This is also why the insulation is below, to slow the loss of heat energy to the space below the floor joists. Radiant heating is all about a balancing act trying to get the energy to go where you need it to go. Directing it is all about making one direction much more attractive to the process of "taking the path of least resistance" than the others. Radiant energy goes in all directions and insulation is what directs it.

    You mentioned that the circulator is not on all the time. Is this the case even when the space isn't up to the temperature that the thermostat is trying to get it to?
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  8. #8
    Join Date
    Feb 2009
    Posts
    13

    Reply

    Trying to answer your questions. Design was recommended by the HVAC contractor who did the hookups. THe runs are 1/2" pex with two runs in each joist bay. There are two "loops", each is about 160' long. they are connected to a "prefabbed" unit that has the circulator, valves, temperature control, mixing valve, etc. The metal is light weight, able to be cut with tin snips. The metal plates are formed to create a "tunnel" to hold the PEX and cover the entire surface area between the joists. For that reason, the contractor told me not to worry about an "air pocket" and run the fiberglass right against the metal plates.

    The manufacturers limitation is 90 degrees for the surface that the laminate is sitting on, which happens to be foam underlayment. If I understand correctly the IR gun can actually tell me the temperature of the subfloor?

    thanks for your help..

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,870
    No, the IR will tell you the temp of the floor/laminate.
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  10. #10
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,003
    Radiant, like any other HVAC system, is not easily modified or changed once installed. This being the case any shortfalls as to how it performs is restricted to working with what you have and what is least evasive and expensive to change.

    The IR gun is a must to proceed. Why? You will need to be able to monitor changes to the actual floor surface temperatures as any variables are changed. The floor manufacturer has stated they do not want to see their product get warmer than 90. With that limit being set the IR measuring device is your best option on watching this.

    Suggestions as to how to proceed are limited by not being able to physically be there and do measurements myself. Radiant performance is no different than any other form of heating or cooling, it can be measured and the actual output and performance can be calculated.

    Your options as a homeowner are:
    Add more insulation under the tubing/floor. The harder you make it for any heat energy that you are delivering to the radiant system to go any direction other than through the floor and into the kitchen space the better. In suggesting more insulation I mean to increase it to the bottom of the joists. Remember, when using fiberglass, do not compress it. Fiberglass relies on the air spaces between the fibers to give it it's insulating capabilities.

    Anything else as far as increasing output of the floor requires changes to the radiant system and due to the rules of the forum I can't go there.

    You didn't say a heat load calculation was done on the space, instead you said "Design was recommended by the HVAC contractor who did the hookups.". A heat load calculation would have provided the information needed to be used in the design layout of the radiant system. That design layout would have given the contractor all the information needed to know exactly how to proceed.

    I'm suspecting that a heat load calculation was not done as it seems even at the mild temperatures you've already had, the floor is not able to maintain the space temperature as initially installed and setup.

    Design calculators/programs for the installation of a manufacturers products allow the contractor to input the space (heat load calculations), identify the heat source specifications available to supply the radiant, any limitations (maximum floor temperatures) and then will recommend the minimum things to be done during the installation that will provide the heat energy needed at design conditions. The program will also flag a space as beyond the capabilities of the system chosen and/or will allow the inputting of changes to different components and function to see if the right answer (design) can be found.

    Sometimes it's just not feasible to heat a room with radiant alone. This can be due to more heat loss than the floor can replenish, lack of available uncovered (no cabinets or appliances) floor surface to act as the radiator, restrictions on the maximum btu's/sq ft (same as max floor temp) allowed to be radiated through the floor covering (your laminate flooring) and the list goes on. What's the answer in these situations? Supplemental heat for those colder days when the floor can not supply the amount of heat energy that the space requires.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  11. #11
    Join Date
    Apr 2009
    Posts
    523
    I'd be curious to see the temp of the floor versus the temp the sensor is seeing. An IR temp would help a lot.

    If you want to find one CHEAP goto a hobby store and look there. You can use an IR gun to setup and tune nitro powered remote control cars/trucks...

    Like this one...



    You can find for 20-25 bucks. I have one that I found for tuning a nitro truck for 15 bucks. Works very well to my surprise but these only have less then a one foot accurate range which is fine for you since you are dealing with the floor.

  12. #12
    The radiant system you have is what is called a "low mass radiant floor", as opposed to a "high mass radiant floor" that would have the PEX buried in concrete/gypcrete.
    Tekmar has established these design water temperatures for radiant heat zones:
    High Mass Radiant-Design Temp=120 deg. Max Temp=140 deg.
    Low Mass Radiant-Design Temp=140 deg. Max Temp=160 deg.

    So you can see from this that your water temperature is well below the recommendations. This is not to imply that your actual floor surface has to reach these temps, but gives you an idea where your water temps should be. Hopefully the infrared thermometer will give you enough information to allow you to raise your water temperatures enough to satisfy your heating demand.

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