Radiant Floor Heating

[Mark Blatter]

Yes, it has an expansion tank. See photo below. I does over time drop to zero, or at least to 2 -3 psi. There are four loops, each about the same length. Each has a cutoff valve so it can be isolated. The pressure when running drops about 8 psi, then back up when idle.

When I first filled the system, I filled one loop at a time, running it for quite a while to ensure all the air was removed. I actually closed the air bleed valve for a few days after running the system for a month or so. Then I opened it and it had a small amount of compressed air that hissed out. I have periodically checked it the same way and have not noticed any hissing sounds for the past year. Not saying there isn't air being released, just no enough for me to hear it.

I did just read on the internet (where everything is true and accurate) that you should not have the expansion tank pointing up like mine is, but hanging down in order to keep from creating air pockets.


Manifold.jpg

[Mark Bolton]

In defense of the internet expansion tank you do wan the expansion tank down because you have the potential of creating a double air cushion. In your configuration you could collect air on the water side of he expansion tank leaving a large volume of air on the water side of the bladder which would compound pressure fluctuations.

That said, the fact that you say the pressure drops by 8psi then returns at idle makes total sense. The entire system expands with heat (including the water) and the pressure in such a low pressure low temp system could likely drop when heated and raise when cold.

The dropping over time to zero can be endless issues in such a low pressure system.

[Mark Bolton]

Cant tell by the photos but looks like maybe a cast iron flanged (gaskets) circulator (low pressure) you may think about swapping that out for a bronze circulator so you can run street pressure in the system.

[Jack Frederick]

In addition to Mark’s excellent suggestions, which direction is your circ pumping. Is it “to” the close radiant loop to the circ. Perhaps I missed it but have you run a high pressure (house supply pressure) during the purge cycle. If not, I think you will have a really difficult time getting the air out of it. You need the turbulence to pick up the air. I would move the X-tank to the bottom of the Spirovent. Lay it off to the side. You are on the suction side of the circ, but on the wrong side of the tankless. Tankless units have vey high pressure drop so your location may actually create a situation where air is introduced into the system. Again, “Pumping Away” will detail this issue. Move the X-tank. Also, Mark is correct on the CI vs bronze or SS circ. Is your pex oxygen barrier?

[Jon Endres]

I have a very similar system and a very similar 'problem' (not sure it's a problem). Mine is fed not from a tankless, but from an outdoor wood boiler feed loop going to a plate exchanger. Over time the pressure in my system drops to zero, but will rise to 5-8 lb when it has been running for a while. I do have an expansion tank, a Spirovent which burps or hisses occasionally, and absolutely no evidence of leaks, and my loops were pressure tested before and after the concrete was poured. I'm guessing that the system somehow is still bleeding off air, and that's after three years of running it. I do use a small pump to put water in the system once in a while, and it'll bring the pressure up to around 10 psi, but it will drop down again during the heating season. I'm not sure there's a solution, but for what it's worth, the system heats my garage just fine. Constant 60°F this winter here in Vermont.

[Mark Blatter]

I forgot to mention that I pressurized the system prior to pour concrete. City inspector required it to be taken to 100 psi and left there for a few days. He then returned and checked it. No drop in pressure at all. I left it pressurized when pouring concrete and had no issues. I actually left it pressurized for about 12 months until I was ready to set it all up. Then installed everything per the diagram from Radiant Tech who designed the system for me.

The pump pulls from the water heater, thus pushing it into the loops.

I did not use house water as I, for whatever reason, wanted to fill the system with distilled water. Thus could not use the house water. I think next summer I will hook up the hose and flush out the entire system with clean water and see if that perhaps removes any lingering air bubbles.

[Jack Frederick]

The horse has all ready left the barn on your system, but I used to throw a couple drops of oil of wintergreen or peppermint in the tubing, pump up the pressure for the test/pour and go to the guys working the slab and give them a whiff of it. If they got a whiff during the pour I could get in, find and repair the damage. I only had a problem on one job where the same guy punctured the tubing twice. It was a couple thousand sq ft pour and I was able to get him off the pour. No more problems.

[Stan Coryell]

Some of those tankless heaters have a trap primer in the unit. I recall a Bosch? set up that would lose pressure after a couple of weeks because of the trap primer. It was a small system, about a 500 sq ft apartment. An auto fill, expansion tank, and auto vent corrected the issue. How come you are running the pressure so high? 185* and 12 psi should be enough for a two story house.

[Mark Blatter]

I am running the system at 20 psi. Again, the guys that designed the system said it would take about 12 - 15 pounds to to raise the water up to the highest point, which is about 7' on the wall. Perhaps I misread it and it has never made any sense to me, but since they know the system and designed it, I went with what they told me.

I can also say that even on the days when the system would be around 3 psi inactive, it always ran fine and heated without an issue.

[Perry Hilbert Jr]

I had put radiant heat under the kitchen floor of our old farmhouse. The rest of the house had hot water baseboard heat and the whole thing was heated by a zero pressure out doorboiler. The kitchen radiant pipes would sometimes get air bubbles. This point was about 8 ft below the water level in the boiler. but each loop between joists had a high spot and low spot. I ran into a radiant heat system design guy once and I mentioned that I put my own in and he asked how it did and I told him I got air pockets in the part under the kitchen. He indicated that it was normal. Dissolved air gasses and little fine bubbles in the water would gather at any high spot between low spots and eventually be enough to cause larger air pockets that when the pump is running low, simply don't get pushed through the system but keep growing. when I added the radiant line the flow was split between it and another zone with a valve to restrict the flow an cause the excess pressure to flow through the other zone. (a no no) He advised that I open the taco valve for that zone to let pressure run full blast through that line every so often and it would blow the air out with water pressure. It worked. eventually, I rerouted the line to be one with the living room baseboard heat and the problem stopped altogether.

[Stan Coryell]

4 psi will give about 10 feet of head pressure.
25 psi, about 60 feet. Set the pressure at 7 psi.
The expansion tank needs to be equal to the system pressure. The tank needs to be on the return (oops) side, I can't tell. It's also upside down trapping air. I would put an automatic vent in the return above the heater. What's the drain going to the bucket?

[Mark Blatter]

4 psi will give about 10 feet of head pressure.
25 psi, about 60 feet. Set the pressure at 7 psi.
The expansion tank needs to be equal to the system pressure. The tank needs to be on the return (oops) side, I can't tell. It's also upside down trapping air. I would put an automatic vent in the return above the heater. What's the drain going to the bucket?

The system produces about three quarts of water a day in the winter when running. I don't have sewer in my shop and I don't want to drain the burn water directly outside as is would likely freeze and plug the drain. So I use a 5 gal bucket and empty it once a week or so. It also gives me water to help trees and bushes keep hydrated in the winter dry.

And it sounds like I can drop the pressure a bit too.

I will get the tank inverted this coming summer.

[Jack Frederick]

Stay up with that condensate collection and disposal. The ph on it is about 3.2 and it will eat a concrete slab in a hurry.

[Stan Coryell]

The expansion tank is trapping air. The water pressure exceeds the "spring" pressure in the tank, rendering it ineffective. I think the system is full of air. I would also read though the owner's manual, it's possible that water is discharged into the drain as a "trap primer" every few days. This would also add to your pressure loss. Also, as mentioned above, check the PH of the discharge. The plants may not like it.

[Mark Blatter]

I don't ever let that bucket overfill. Knock on wood, so far at least. I have thought about various ways to drain it out so it wouldn't freeze and be far from the concrete but no bright ideas yet.

As for plants, I spread it around and so far no issues. In thinking about it, I will pick up some ph strips to test the water. Just curious now.

I am sure it is from the burning as the only time it produces water is when the system is running.

Any thoughts about build up of 'junk' inside the tubing? Is that a concern I should be worrying about? If so, how to clean it out? Flush the system with a bleach solution or something else? How about that acidic water?