Adding underfloor radiant heating with PEX?


Hi: We're remodeling the bathroom in our small 1930s house. I'd like to put radiant heating in to replace the radiator that's there now. From my reading, I'm thinking of adding loops of oxygen-barrier PEX under the floor (easily accessible from the unfinished basement) and tying it into our existing natural gas hot water boiler radiator system. The system is closed loop with iron pipes and radiators. I was thinking of using heat spreaders & then insulating below the tubing. Does anyone have any advice on this? Am I likely to need a tempering valve to reduce the temperature of the water in the system? Are heat spreaders unnecessary? Any problems with tying into the iron pipes? Thanks in advance, Freud
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Freud wrote:

If its closed loop system how can you add a tempering valve to lower the temp to the loop? You would have to dump water out of the system to put cold water (that has disolved oxygen in it) back in and then get the air out of that? Am I missing something?
I like idea of radiant heat but not in your case.
Rich
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snipped-for-privacy@home.com says...

I had just read about people adding tempering valves so I threw it out there. I'm not sure how hot the current system runs, and I'm also not sure what's optimal for radiant heat, though I've read that 100-110 degrees F is a good range. Thanks for your help! Freud
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Freud wrote:

You don't need a separate cold water supply to temper the water in a closed loop, the valves designed for this purpose simply recirculate the "sub loop" water mixing in heated water from the "main loop" side as necessary to control the temp. You typically need an additional circulator pump. The radiant heating system manufacturers have all the necessary components and expertise for this type of setup and typically can provide a design service and complete installation package for what you want. Pickup a copy of Fine Home Building and you'll find ads for many of the manufacturers and can review the info on their web sites.
Pete C.
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I am no expert but have looked into such a system for my own place. Most radiant system run a cool 120 degreees F. That doesn't mean you can't run it at a higher temp you likely can. The pipe will handle it so the only question is the flooring. What type of flooring do you have? How hot does your boiler run?
The pipes will be thermostatically controlled so they would have to cycle on and off more often. Some flooring may not stand up to such hot pipes or such frequent changes. A mixing valve is not a big deal from what I understand.
The designs I have seen use the metal spreaders but they are not necessary. Staples are also available which are just nailed to the joists. Some people claim that the spreaders make an annoying noise as they expand and contract. Manufacturers claim they have solved that problem. If you assume that insulation will be placed into the joists under the pipes then spreaders seem less of a concern to my mind.
A manifold is usually used in hydronic setups. This could be as simple a a tee and a valve which branches off the main line. the advantage is that an electronicallly controlled valve can be used with thermostats in the living quarters to have as many different zones as you wish. If you only want one zone then fine but if you want more control the hydronic systems are well suited for multiple zones. I would be cool to have a zone for each room and one for the hallway too. In Minnesota we heat our houses for 10 months of the year.
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We'll probably put in ceramic tile, but we haven't decided yet. I'm going to try to find out how hot my boiler runs.

Since our system just pumps the hot water around in a sealed loop (aside from a pressure relief valve), I think that it could be a problem as Rich pointed out above. But it might not be a dealbreaker if the floor can take it. The other concern, of course, would be that we don't want the floor too be too hot or we'll be jumping around like cats on a hot tin roof!

The zone idea is nice, but in our small house might be overkill. Thanks! Freud
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Warm tile sounds nice but tile may be one of the least flexible flooring and prone to cracking if real hot water is used intermittently underneath. There is laminate flooring which is popular in plastic,real wood, bamboo, vinyl and god knows what all.
They attach to each other and not to the floor allowing them to float. Resiliant flooring like vinyl are time tested and cost- effective. New flooring products are coming out every day it seems especially with the floating floors . It's not as durable or water resistant as tiles probably and maybe not the best choice in a bath or kitchen. I know that they are constantly improving and upgrading this type of flooring since it seems to be a popular choice. Some come with great warranties for whatever it's worth.

an opinion before you decide. One concern is the capacity of the boiler and what the maximum usage of that capacity may be during the coldest possible weather. My guess is that it can be done if the boiler is big enough. Since you have a boiler in place I think it makes you a better candidate for hydronic heat than not.
Of course you do the work in the summer. You have to shut down the system and drain it down before you can work on it. You can cut the pipe and tee off the main loop to the mixing loop. You likely use an anti back flow device at that point. Then you can build or install the mixing loop before the water entering the floor. The thermostatically controlled valve can come after the mixer. Pete C. gave a superb explanation of how the mixing works. You should take his advice and run your ideas past some pros.
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