Opinions on using radiant heat??

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strmh

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May 24, 2008
61
Northern Maine
Right now I'm heating my shop via in-slab radiant heat. I've got an EKO 60 in the shop that heats both it and my house. Hot water from the boiler first goes to the house (hot water baseboard) and then I'm pulling the shop's radiant off the return from the house. I've got two radiant zones in the shop and I'm keeping the thermostats set at about 66-67 degrees. (total of 7 loops)

I use a Ranco aquastat to power the radiant zone controller. If the returns to the boiler drop below 150 degrees, the ranco cuts power to the radiant zone control. Once return temps get back up to 158 or so, the Ranco powers things back up.

Once the slab is up to a nice temperature, there's hardly any temperature drop between the radiant supply/return. When the zones quit calling for heat, the slab will cool just enough so that the radiant goes through numerous on/off cycles before return temps remain high-enough to keep the ranco from shutting things down.

Here's my question.....should I just set the shop's thermostats to just have the radiant run all the time? Would this then make the radiant almost transparent to the system? It seems to me that once up to temp, the slab would just serve as big heat bank that hardly pulls any heat from the water.


Thanks,

TH
 
Are you using a mixing valve for the slab ? 150 is way too hot for the slab, should be more like 100 or less depending on your loss. ( r values)
 
Yes, I should have clarified.....I use mixing valves and send 95-100 water to the slab.....
 
I have mine running at around 130-140*. The idea with warmer temp was a quicker recovery.
 
i have also heard no more than 120* to a slab. if left my shop like that the circulator would run 24/7 and the shop would be cold. what does it hurt to run it hotter? back to the topic. id get the shop to temp and leave it irregardless of return temps. i find it easier to maintain room temp rather than letting it fluctuate.
 
It seems to me that once up to temp, the slab would just serve as big heat bank that hardly pulls any heat from the water.
Click to expand...

That would depend on how much heat the shop is pulling from the slab.
 
My basement floor water is at 130* and seems to work good. It seems Ive heard about water temps should be 100 or less though. Why is that?
 
strmh said:
Yes, I should have clarified.....I use mixing valves and send 95-100 water to the slab.....
Click to expand...
I would think that if you left the slab on, it would remove heat from the water until it eventually got up to your water temps and that would be way above your setting of 66-67 deg. , unless loosing it that fast (as DaveBP said).
 
strmh said:
Right now I'm heating my shop via in-slab radiant heat. I've got an EKO 60 in the shop that heats both it and my house. Hot water from the boiler first goes to the house (hot water baseboard) and then I'm pulling the shop's radiant off the return from the house. I've got two radiant zones in the shop and I'm keeping the thermostats set at about 66-67 degrees. (total of 7 loops)
Click to expand...

Using the return as supply for the radiant is a great application. Many publications promote this, as well as other posters on this forum, generating great results. I plan to take advantage of this idea next year with some modifications as well to hopefully gain better stratification in my storage do to the lower return temperatures.

strmh said:
I use a Ranco aquastat to power the radiant zone controller. If the returns to the boiler drop below 150 degrees, the ranco cuts power to the radiant zone control. Once return temps get back up to 158 or so, the Ranco powers things back up.
Click to expand...

Great application for boiler protection, especially during the beginning of the heating season or slab 'start-up'.

strmh said:
Once the slab is up to a nice temperature, there's hardly any temperature drop between the radiant supply/return. When the zones quit calling for heat, the slab will cool just enough so that the radiant goes through numerous on/off cycles before return temps remain high-enough to keep the ranco from shutting things down.

Here's my question.....should I just set the shop's thermostats to just have the radiant run all the time? Would this then make the radiant almost transparent to the system? It seems to me that once up to temp, the slab would just serve as big heat bank that hardly pulls any heat from the water.
Click to expand...
Yep, go for it. This is why they call it low-temperature high-mass radiant. You supply just enough heat at a near-continuous rate to equal the areas heat loss. You should find that your delta T will remain between 10-25 depending on your flow rates through the loops. After all we are talking about a high-mass low-temperature heat emitter not a low-mass high-temperature fin-tube heat emitter, so design and the application of those designs are a bit different. Everyones situations are different...but I think for your situation, you will find your slab-radiant will become more efficient, or transparent if you like, by providing near-continous circulation with the lowest possible supply temperature to satisfy your areas heat loss.
-Bob
 
Thanks for the replies...

The area I'm heating is insulated fairly well. I think most of the slab's heat loss stems from the areas near the overhead doors that are more directly exposed to the outside.

I've been wanting to try this, but I wanted to bounce the idea around with the forum before doing so. I'm going to give this a try and see what happens.

-TH
 
May be a good application for a 100 gallon or so buffer tank just for the infloor. Make the tank a separate zone heated by the return. That way if the boiler return does get below 150 and the boiler needs to "catch up" u still have heat to your infloor from the tank virtually eliminating any cycling of pumps. If that is a concern.

Brandon
 
2.beans said:
i have also heard no more than 120* to a slab. if left my shop like that the circulator would run 24/7 and the shop would be cold. what does it hurt to run it hotter? back to the topic. id get the shop to temp and leave it irregardless of return temps. i find it easier to maintain room temp rather than letting it fluctuate.
Click to expand...

120* is a standard rule of thumb for radiant floor heating.
 
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