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Radiant underfloor heating


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Not that this will help you much, but out of the 5,000+ homes I have inspected I have maybe seen 6 or so homes with radiant floor heat. I had one last week, it was a slab construction as well! I simply told my client that I knew just enough about this type of system to tell them that they needed to contact the company that installed it to inspect and show them how to work it. This was my way of telling them that I did not have a clue as to what I was looking at! My client was not upset with me one bit, in fact they praised me for being honest with them about my knowledge or lack of knowledge of the system.

This home also had a conventional forced air HVAC system that provided heat and cooling to the home.

I have attached a couple pictures of the water heater and the valves that controlled the system. The water heater in this picture had just been replaced, it cost $8,000!

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Usually each thermostat has a corresponding valve. Scott's pic shows 7 valves, so there are likely 7 thermostats and 7 zones (loops). You can run up and down the stairs testing all the floors for temp changes as you play around with the thermostats.

If you call for heat at all the thermostats at the same time, the whole system slows down. Tile floors are slow to heat up.

See if the thermostats open valves by taking temp readings on the tubing where it leaves the valve. You can hear if a circulation pump is running or you can feel it for vibration.

Check for a system for adding makeup water thru a check valve. Expansion tank, PRV, etc.

Then I tell my client what I tried and what the result was, or if there was no result, and it's always best if they can get the expert in to check the complicated systems.

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Usually each thermostat has a corresponding valve. Scott's pic shows 7 valves, so there are likely 7 thermostats and 7 zones (loops). You can run up and down the stairs testing all the floors for temp changes as you play around with the thermostats.

That's sort of true- loop effectiveness wanes at about 300ft of piping. So to get water to the outer reaches of the home, one installs a manifold in the area to avoid excessive loop lengths. There may be one loop or ten loops to a manifold The zone valves in the photo may each control a manifold.

It's quite conceivable that the seven zone valves are controlled by fewer than seven thermostats. One even.

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Usually each thermostat has a corresponding valve. Scott's pic shows 7 valves, so there are likely 7 thermostats and 7 zones (loops). You can run up and down the stairs testing all the floors for temp changes as you play around with the thermostats.

That's sort of true- loop effectiveness wanes at about 300ft of piping. So to get water to the outer reaches of the home, one installs a manifold in the area to avoid excessive loop lengths. There may be one loop or ten loops to a manifold The zone valves in the photo may each control a manifold.

It's quite conceivable that the seven zone valves are controlled by fewer than seven thermostats. One even.

It did have 7 thermostats. I just can not imagine subfloor heat with a concrete slab in our area. We might be at 15f degrees for a few days and then a warm front can push it up into the 60's or better! That slab is still going to radiate that heat for a few days I would think.

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Folks mistakenly imagine radiant floor heat means a "hot" floor. If it's properly designed and installed, most floors don't even feel warm. Arguments abound, but the floor is usually mid 70's to low 80's. So, you don't feel hot if the temps change.

There's no good way to inspect a radiant system without IR. All you can do is see if it runs, and look for basic design considerations such as those noted by Fabry, or primary/secondary loops.

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I see a lot of radiant systems and Scott's got it exactly backward. If it's warm for a couple of days and the temps suddenly drop it's slow to warm up, more so with a high mass floor like a slab, but it's minutes not days.

My thermocouple went bad this past winter and the house got down to about 50 before I got it replaced and the boiler back up and running. We were back to a balmy 64 in under 40 minutes. We experienced a similar issue at the day job the year before, and it took about 3 hours to warm up 5000 SF of concrete slab.

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