Radiant Hardwood Floors


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Old 01-16-23, 07:59 AM
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Radiant Hardwood Floors

I just bought an apartment and the builder had hydronic radiant installed throughout. 95% of the apartment is 4" white oak; two bathrooms are tile. The boiler is the Navient NPE-150S.

Whats a good temperature to set the boiler at? I believe its currently at 130F, which I think is a little high for wood flooring? Additionally, someone in the building told me the installer (no clue who), said we shouldn't set the thermostat above 70F. In my mind, why does that matter? Isn't it the temp coming from the boiler thats more important for not messing up the wood?
 
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Old 01-16-23, 12:23 PM
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Wider wood planks could cause cupping of the floor with higher temperatures. A water temperature too high can cause what they call sweaty foot syndrome. I would say keep it as low as possible and still heat the home. Drop the temp 4 degrees at a time and allow 2 days before re-adjusting the temp again.
 
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Old 01-20-23, 01:52 PM
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thanks all. I've had the boiler set at 120F for the past 5 days and heat has been good; although its only be 30-45 F at night-day -- (fairly warm for NY this time of year). Not sure what the return temp is but I will check next time I'm in the basement.


 
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Old 01-27-23, 11:23 AM
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Radiant in slab (concrete) I normally suggest not to change the thermostat temperature due to slaw reaction time on thermostat changes, Find the best temperature for your home and play with water temperature giving at least a day between changing water temperature. Do not change more that 3-4 degrees at a time.
 
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Old 01-16-23, 08:27 AM
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no odr and I dont think there is a mixing valve.


 
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Old 01-16-23, 10:52 AM
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Is the flooring solid wood or engineered? Higher temp for solid wood should not be a problem. Engineered may have some manufacturer's limit.

I run some radiant flooring in a bathroom and kitchen/dining room as part of a mixed hot water/cast iron/copper baseboard system with multiple zones. My atmospheric boiler is set for 150 degrees. In the radiant/CI kitchen/dining room zone the radiant is via aluminum plates under a 3/4 inch subfloor + 3/4 inch solid oak flooring and the temp (without shoes,, etc.) is noticeable if you think about it but certainly offsets the feeling of a cold floor. In the radiant/copper bathroom zone the radiant is above the subfloor and under tile on 1/4 inch cement board. The floor there is toasty warm but not too hot.

In a full radiant system I think 130 is the recommended maximum water temperature AT THE FLOOR for comfort reasons.

Wall thermostats are set for 68-70 degrees. I do not have embedded temperature sensors in the radiant.
 
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Old 01-16-23, 12:38 PM
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I went down and the boiler was actually set to 180F. The other three units in the building (with same floor and boiler) were set to 160F. I decreased my boiler to 130F. As far as I can tell, there is no mixing/tempering valve for the supply line to the floors.

The floors are 3/4" thick, solid oak, 4" planks. The bathrooms are tiled. I am still trying to figure out who did the radiant install to get more details, but afaik, the system isn't zone, so the same supply runs under the hardwood and the tiled bathrooms. Since I've moved it, the system has been on too much so its hard to say if things will feel warm to the touch or not.

Thanks
 
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Old 01-16-23, 01:49 PM
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The other three units in the building (with same floor and boiler) were set to 160F
If yours is a top floor or an end unit with more exterior wall exposure, the setting may have been set higher to offset additional heat loss.

​​​​​​​hard to say if things will feel warm to the touch or not
For the obvious reason, when I feel the portion of the floor under a bath mat or throw rug, the difference is noticeable
 
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Old 01-16-23, 03:02 PM
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Multi tenant with commercial fire alarm system.
No mixing valve.
Boiler supplies domestic and heating hot water.

The top floor gets the benefit of the rising heat from the apartments below and doesn't require higher water temps. As mentioned keep the hot water heating setting as low as possible while maintaining adequate comfort.
 
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Old 01-16-23, 03:48 PM
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Wider wood planks could cause cupping
Issues with flooring is due to moisture, not temperature. Just like floors that squeak in the dry winter will swell with the summer humidity and be quiet!
 
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Old 01-16-23, 05:08 PM
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Thanks, everyone.

We are the third floor of a four story, four apt building (each apt has a floor). Looking more closely, I noticed the supply/return valves are swapped on my boiler (the blue valve is on the supply side and the red valve is on the return side). I imagine the valves are identical (??) and its just color coding on the valve for convenience?

I can't believe I missed it, but it looks like scoop is install backwards relative to pump flow. annoying... Nevermind...I just looked at the boiler again, the scoop and the pump are flowing in the same direction (the picture I originally took made it seem like the scoop was backwards).
 

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Old 01-17-23, 08:57 AM
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I imagine the valves are identical (??) and its just color coding on the valve for convenience?
If it bothers you, you could swap the handles. Common usage would imply red for hotter (supply ) and blue for cooler (return).
 
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Old 01-17-23, 04:04 PM
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I spoke to the builder today; each floor is 6" of concrete, then 3/4" plywood and 3/4" oak. the PEX is in the concrete. Any recommendations on temperature? They told me to feel it out and find what is comfortable/works.

Biggest problem is I get so much heat from the units below and insulation from the unit above, the system hardly runs. Its nice I don't have to run my boiler but it also means my floors stay generally neutral temp; they never feel warm(ish)
 
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Old 01-17-23, 04:48 PM
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Condensing boilers can run at very low temperatures. Try the lowest setting for a couple of days and raise it a few degrees every other day until you find a floor temp you like.
 
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Old 01-17-23, 05:09 PM
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There's nothing like free heat.
The important thing is the floor is not cold.
 
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Old 01-20-23, 08:53 AM
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There's nothing like free heat.
In the 1970's I rented an apartment that was the first floor of a two-family house. Each unit had its own oil-fired forced-air "octopus" furnace that shared a common return via the basement space. Each unit had a separate contract with the oil company. I set my fan switch to come on at a very low temperature and the fan ran almost constantly. An unintended effect was that I got the benefit of all the heat in the return air from both units. My oil bill was about $75 for that season during the "oil shortage". My landlord who lived above complained that his own bill was the most expensive he ever had for his own unit.

Just for fun I took these photos of the temperatures of my radiant floors today. The room temperature is set for 69 degrees, the outside temp was 35 degrees, the boiler output is 150 degrees:


Residual radiator temp in dining area. Zone not calling for heat.

Floor temp in dining area with radiant heat. Zone not calling.

Floor temp in area that does not have radiant.

Pipe temp at baseboard in bathroom. Same loop as radiant. Zone calling for heat.

Radiant floor temp in bathroom.

Maybe this will help the OP in setting boiler temps.

 
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Old 01-20-23, 12:20 PM
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the boiler output is 150 degrees
Clarification: My boiler set point is 150 with a 30 degree differential so the supply temp to emitters will range from 120 to150 minus any pipe losses along the way.
 
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Old 01-26-23, 03:54 PM
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So Ive been running at 120F and, since the nights have gotten a bit colder here, I have noticed the heat does kick on in the night. This often means I have noticeably warm floors when I wake up, which is great.

I have noticed, though, with the thermostat set to 72F, after the morning warm up, the latent heat in the floor still brings the room up to 75F by mid day (even with heat off).

I noticed that the thermostat (honeywell T3 non-programable), was set as forced hot air so I switched it to radiant.

Do you think that will help with the overshoot or should I lower the boiler temp more or maybe get a learning thermostat that better predicts heat cycles ... or both?

 
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Old 01-26-23, 04:41 PM
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I have lost 2 replies. Will try again tomorrow. Use programmable tstat like a time clock to shut off heat sooner.
 
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Old 01-27-23, 09:44 AM
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I have lost 2 replies.
Trying again...

Your concrete slab is a big heat sink--slow to heat up and slow to cool off. It will not respond in a timely manner to a room air thermostat. You need to continue to evaluate your heating cycle hoping to find a schedule that will produce the results you desire. Most likely turning off the radiant earlier so that the room temperature does not overshoot later. A programmable thermostat can be used to do that by acting as a temperature-related time clock.

As an example here is a description of how I control the radiant in my bathroom floor. It will not be the same for you since you are heating a concrete slab and I am not, but you may get some ideas about how you can control your heat.

My bathroom heat is a subset of the bedroom loop. The radiant was not part of the original construction and was added later. I have two thermostats in a short hallway outside separate openings (without doors) into the bathroom and into the bedroom. Therefore they measure the air temperatures in the two rooms somewhat indirectly although there is direct line-of-sight to the bathroom floor. When the bedroom t'stat calls for heat hot water runs through the entire loop: bedroom--> bathroom baseboard--> radiant in floor --> return to boiler. When the bathroom t'stat calls for heat hot water runs only through the bathroom sub-loop: baseboard--> radiant floor--> return to boiler.

I set the t'stats so the bathroom is always warmer than the bedroom; the bathroom heat comes on earlier and shuts off later than the bedroom heat. Here is the schedule:

Wakeup: Bathroom 70 degrees @ 4 AM, Bedroom 68 degrees @ 7 AM
Daytime: Bathroom 65 degrees @ 11 AM, Bedroom 63 degrees @ 9 AM
Evening: Bathroom 70 degrees @ 9 PM, Bedroom 68 degrees @ 9 PM
Overnight: Bathroom 65 degrees @ 11 PM, Bedroom 63 degrees @ 10 PM

Whenever the bedroom shifts from lower to higher temperature it takes about 40 minutes to heat up.
Bathroom floor stays warm until about 1 AM at night. (If I want it to stay warm longer I could set a setback time later than 11 PM.)

You can also try setting your thermostat at a lower temperature (68?, 65?) that will provide the 70 degrees you want.

What do you have for air conditioning? A combination of radiant floor and heat pump mini-splits would be an ideal more responsive situation. The floor could be set for a constant (low) temperature and the heat pump mini could raise the room temperature as needed.
 

Last edited by 2john02458; 01-27-23 at 11:44 AM.
 

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