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Member Posts: 301
Just curious on what the temperature of the water should be in my radiant heated 4inch slab?  Finished floor is a combo of tile, carpet and laminate flooring.  Thanks in advance

• Member Posts: 2,666
It depends.

I am not a professionial, but determing the correct temperature to put into a radiant slab is impossible given the information you gave (or did not give).

For example, I have a zone heated by copper tubing in a concrete slab that is almost certainly thicker than four inches. The heat loss at the 69F I prefer to heat that zone is such that if it is 6F or less outside, I put 120F water in. Design temperature is 14F, and at that temperature, I use 112F input.

A rule of thumb I have heard is never to put more than 120F in a radiant slab. I have put more in when I did not know what I was doing (left it where the former homeowner left it) and I estimate I put 140F in. The first symptom was that the asphalt tiles popped off the floor in the kitchen. Also terrible swings because that boiler had no outdoor reset, so it always ran at maximum temperature, or off.

If you do not have outdoor reset with a slab, I suggest you get it (if practical). Then calculate the heat loss and calculate the btu/hour you need to overcome it. From that you can calculate btu/hour/square foot. I do not know the maximum you should put into a slab, but if you need more, or more than 120F, I suggest you consider supplementary heating (e.g., radiant panels on the walls or ceiling). But before taking my advice, get your system reviewed by a profesional who knows radiant hydronic heating.
• Member Posts: 9,546
How are the zones divided up?

Or are they? Meaning your floor coverings have different r values so each zone would require a different water temp. Setting a water temp to say 130* may give you the temps you need to off set heat loss in the carpeted room, and have you dancing accross the floor in the tiled room.

So first question is if you are able to use different temps in the different floor covered zones. IF not you may have to find a happy medium.

Gordy
• Member Posts: 301

That is the problem.  I have two zones downstairs and both zones have a combo of a thin berber carpet with felt pad, tile and the other zone also has two rooms with a wood laminate flooring.  I currently have 100deg water going through the zone with the wood and 90 going through the floor with just the carpet and tile.  Is the water too cool so the boiler will have  to continue to run?

My boiler is set at 180 degrees and I do have baseboard heat upstairs.  I have a system bypass to heat the return water.  I just want to make sure I have the right temp water so the house heats efficiently.
• Member Posts: 9,546
edited October 2011
Baseboard

I will assume that the baseboard is a seperate zone correcta? The main thing is to not get floor surface temps above 85*, for human comforts sake.  If you had real wood flooring that temp would also apply to protect your real wood floor from damage, but you have laminate flooring. You could go as high as 140* supply temp. IF you had to, and still be safe.   The issue I see is the heat loss in rooms with higher R Value flooring ( carpet, and laminate) verses the tiled floor. While you may overcome the r value to heat the space in certain higher R Value areas, you may over heat others. So with out changing the system to be able to zone the areas with different temps you may have to experiment with a happy medium temp. Is this a new install?New boiler, New complete system?
• Member Posts: 301

baseboard is a seperate zone.  It is an existing boiler with an indirect hwh. 3 zones total.  Smith 150,000 btu bolier
• Member Posts: 9,546
Other zones

What does zone 2 and 3 cover for the RFH?

Gordy
• Member Posts: 301

Sorry, not sure what you mean by RFH?
• Member Posts: 9,546
RFH

• Member Posts: 3,086
edited October 2011
Heat Loss

I think you need a pro to come in and do a heat loss. Nobody here can tell you what water temp to run. We would all just be guessing like you are. You habe multiple finished floor surfaces and all have different r-values. One temp won't do it. Especially the carpeted areas. Who installed the radiant?
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Member Posts: 9,546
I totally agree

With Chris. To recognize real comfort which is what radiant heat is about. You really need to be able to separate those areas with different temps. The heat loss in the areas along with the r value of the floor coverings will dictate the supply temps, and flow rates.

Finding a happy medium may be a temporary solution, but not the best solution.

Gordy
• Member Posts: 301

We hired a hvac guy that was recommended.  He knew what we were putting down for floor covering so he put more tubing in the carpeted and wood areas.  One zone is for our bathroom and bedroom and the other zone is for the living, eating, kitchen and entry way.  So there is not one temp that is recommend.  I currently have it set at 100degree but maybe with the colder weather coming and heat loss,  the temp should be a bit higher.
• Member Posts: 2,666
I currently have it set at 100degree

I have outdoor reset for my boiler and when it is heating my radiant slab zone, the temperature of the water supplied to the slab varies between 75F and 120F depending on the outside temperature. The outdoor temperature around here varies from one day to the next, and also changes if a warm or cold front passes through. Also, nights are sometimes 20F colder than the daytime. In other words, no matter what temperature I set, it will surely be wrong most of the time. I would hate to run out to my garage, where my boiler is located, to change the supply temperature several times a day.
• Member Posts: 301

I thought about an outdoor reset.  I also get a lot of sun which helps to keep the house warm during the day and the boiler doesn't run at all but  at night when it gets cold, the next morning, it could be 2 or 3 degrees below the thermostat setting.
• Member Posts: 9,546
diminishing returns

While more tubing can help lower water temps, and deminish heat stripping to a point, it is by no means a way of actually try to make a one temp fits all types of r valued floor coverings, or different heat loss rooms work together as a comfort system. Sounds like you will be experimenting.

Gordy
• Member Posts: 3,086
edited November 2011
Did Your

HVAC guy leave you the radiant design and heat loss? If not then needs to be reversed engineered to be able to give you the correct anwsers. We all can sit here and throw temps out to you that may work but that would be like putting 15lbs of air in my tires because the car will move. Would I be driving comfortably? Would my gas milage be the good?

How is the radiant being mixed? That is also an awful lot of boiler hp for what seems like a light load.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Member Posts: 9,546
Control is key

And may not be that bad to incorporate into the system. Photos are worth a lot to help, along with what Chris asked.

Concrete slabs can be hard to control ( fly wheel effect) with out a proper control strategy. What may work for a supply temp now probably will be to cool when winter hits. Then as you come out of winter that supply temp will be to warm.

You have all ready stated you have a fair amount of solar gain. While this is a money saver it also compounds controlling temps in the house, and the system.

Fly wheel effect is when you have a mass (concrete slab) being heated, or cooled. Once heated, or cooled it stores that energy, and it takes more time to dissipate that energy. It also takes more time to charge the slab with that energy. Unlike a low mass system that responds fairly quickly to temperature changes.

What happens with out control ( floor sensor, outdoor reset, indoor feedback, zoning) you tend to over shoot the thermostat setting because once the thermostat is satisfied the slab has not released all the energy that has been put into it in that cycle. This can cause many trips through out the winter to adjust water temps being supplied to the slab.

With outdoor reset it does this for you automatically according to the feed back it gets from an outdoor temp sensor. As the temperature outside goes up, or down it adjusts the water temps accordingly. Your baseboard if properly sized does not always need 180* water. Only on design days which is about 3% of the heating season.

If you can tell us your floor coverings, tube spacing, heat loss in each corresponding zone we can tell you what temps need to be for that zone. How you get those different temps is going to have to be dealt with through controls.

We are not bashing you only trying to get you what you deserve through the keyboard.

Gordy
• Member Posts: 6,232
we like to see

the temps maintained so that you have 70 degree F on the coldest day of the year inside your home . this is not a sure thing to design for buh it keeps us habby.

serendipitous window and door remodels with cascading glass expanses and garage doors left open are things that drastically alter the ability of any form of residential heating to overcome.

what will come across to asking a professional is that his answers might be somewhat different than you were thinking that you would hear.

Chris and Gordy are doing what they can to basically say that the number varies as the environment changes both in door and out.

outdoor reset is quick however weather responsive controls are slightly more expensive to predict the next variable to change in the equation . day before yesterday the slab had about 79 degree fluid rolling , yesterday the outdoor temps dove to about 15 18 below 0 F and changed to nearly 87 or so...

now, a professional could by doing some fancy pencil work , knowing the amount of windows and doors the sites topography and a host of other information be able to tell you just how much r value the insulation Under the slab might be...or knowing that info, tell you how much insulation is in the walls or ceilings... however, without a blower door test things could still be a bit sketchy on any vast anomalies ...

what that means is there are differences not only in the application of pipe to slab say , buh there are quite a few other details that enter into being able to say ,

" the temp should be" ....

and fire out a number.

quite a while ago an old contractor told me that you should always design the fluid / water temps to never exceed 100degrees F with radiant floor heating.

thats then, this is now .... however i do tend to like his thinking...

Weezbo

*~//: )
• Member Posts: 5,853

Nice to see ya Weezbo. Have missed your special prose and articulations.

Stick around, wontcha?

ME
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
• Member Posts: 9,546
Ditto what Mark said

Nice to see ya back Weezbo!
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