coil in boiler, for infloor heat?

I just had a thought & will accept opinions on it. About 1/3 of my house is radiant infloor heat. It runs at 140 degrees. When we built this house they had not yet invented pex-al-pex tubing so my tubing can have oxygen infiltrate. I was told that it can cause corrosion of pumps and boilers so I added some secret sauce to the boiler water that keeps oxygen from getting into the water. The thing is that as years have gone by, the additive is slowly lost and they no longer make it. They discovered it causes a third arm to grow on Egypson mice or some such hogwash, so it's no longer legal. There is no replacement. When I add my coal boiler I will dilute what little there is and I'm a bit concerned about it. My thought was....buy the coil and run the infloor off the coil that in the boiler. I have an indirect hot water heater so I won't need the coil for that. I'm sure the coil would put out enough BTU's. Can anyone think of why it might not work?

Why don't you put an additional air scoop on that loop and run it the way it should be? Scott

The idea is to keep new oxygen from getting to components that can rust. When oxygen sneaks in, it makes iron oxide with anything it can. Once it does that the chemical reaction is done until new oxygen is allowed in. Most boilers soon have "dead water" in them, but my system keeps the water alive when the infloor tubing permeates O2. Purging air does not get the 02 out of the water. Another way to think if it is when O2 permeates through the tubing, air bubbles do not occur, only the oxygen molecule gets through to fill the molecular spaces in the water. At least that's what they taught us at radiant heat class 16 yrs ago.
Using the boiler coil for the radiant tubing would keep the water from contacting the boiler or other pumps and zone valves in the system.

That's true about the oxygen.

I just saw a wood boiler which uses a 6 gpm coil to heat his whole house and large outbuilding. The boiler is massive. Maybe you could use your indirect for the job, if it's an Ergomax brand, which won't run out of hot water. The Ergomax formula is: Gallons per hour X DT X 8.3 equals the BTU needed to create 120 degree water @ 5 GPM.

GPM X 60 = GPH

The temperature difference between the cold water inlet and the hot water outlet is DT.

Your mission is to determine if your boiler is large enough to produce enough hot water through a coil for the volume you need.

I have run O2 permiable tubing in two different hot floor systems, one I put in about 25 years ago, and my current one.. Both systems work fine,, not corrosion, pumps sit during the summer, and start fine in the fall... and they are cast iron pumps not bronze.

The trick is to have pressure on the system,, and to pump [push] the water through the tubing, don't pull the water from the tubing. Any amount of negative pressure allows the O2 to migrate through the tubing.. but under pressure this is either eliminated or so minor to be not an issue..

As for you hot water coil providing enough hot water for your floor heat,, I'd use the above formulas and give it a run through your calculator...

OR: Just give it a try... try the hot water coil and see if it provides enough BTU's..

The other option is to run the floor heating system through a water/water heat exchanger, and use the regular hot water from the boiler... a 40 plate water/water exchanger can be purchased for around $200 on Ebay,, [search outdoor wood boiler] and this size exchanger is good for around 150K BTU, if I remember correctly. Maybe 180K btu.. Piping is simple,, and you could add a fresh anti-corrosive,, such as automotive ethylene glycol or propylene glycol. in the isolated floor loop.

I use the plate exchangers in my systems,, they work great,,

Greg L

.

Thank you both for the advice and tips. I'll crunch some numbers & make a decision. I like the idea of the plate exchangers. Used to be they were over $500!

I've not had pumps go bad, but I have 5 zone valves and two have gone bad & a third not far behind. I honestly think it's not corrosion as much as goopy gunk from the additive. I have to replace air vents every year or two as they gunk up. When the coal boiler goes in perhaps I'll flush that crud from the system & find some lab rats to feed it to.

Speaking of air vents, it used to be you had to drop system pressure to replace one. They now sell a tiny ball valve that goes under the vent. To replace a vent, turn valve off, replace vent, turn valve on. What used to be a 45 minute project is now 45 seconds. Next time you go to buy a vent, buy some of the valves.

This is why I love this site.

Last week I read a book about radiant heat and was considering putting it in my first floor to keep the floors warm on those cold winter days. Oxygen inflitration was discussed at length in that book. I thought of adding an indirect water heater to eliminate the corrosion problem. Dam you guys are like mind readers.

LSFarm suggested a couple of weeks ago about using primary/secondary pumping when I connect my boilers. At the time I didn't have a clue what you were talking about but wouldn't admit it. The book I finished touched on the subject. It sounds like a pretty good solution. I just ordered another book dedicated to primary/secondary pumping. Hopefully I learn enough to be able to lay out my system without screwing it up to much.

LsFarm wrote:I have run O2 permiable tubing in two different hot floor systems, one I put in about 25 years ago, and my current one.. Both systems work fine,, not corrosion, pumps sit during the summer, and start fine in the fall... and they are cast iron pumps not bronze.

The trick is to have pressure on the system,, and to pump [push] the water through the tubing, don't pull the water from the tubing. Any amount of negative pressure allows the O2 to migrate through the tubing.. but under pressure this is either eliminated or so minor to be not an issue..

As for you hot water coil providing enough hot water for your floor heat,, I'd use the above formulas and give it a run through your calculator...

OR: Just give it a try... try the hot water coil and see if it provides enough BTU's..

The other option is to run the floor heating system through a water/water heat exchanger, and use the regular hot water from the boiler... a 40 plate water/water exchanger can be purchased for around $200 on Ebay,, [search outdoor wood boiler] and this size exchanger is good for around 150K BTU, if I remember correctly. Maybe 180K btu.. Piping is simple,, and you could add a fresh anti-corrosive,, such as automotive ethylene glycol or propylene glycol. in the isolated floor loop.

I use the plate exchangers in my systems,, they work great,,

Greg L

.

My experience with oxygen permeable tubing used for in floor heating is very different. I had extreme corrosion, including the cast iron pumps. I resolved the problem by isolating the oxygen permeable part of the system with a flat plate heat exchanger and, when I continued to have corrosion problems with the cast iron pumps in that part of the system, by replacing the pumps with bronze ones. I had the problems notwithstanding the fact that my pumps were set up to push.

With regards to ethylene and propylene glycol--without inhibitors these will very quickly turn acid when used in a heating system. Commercial anti-freeze based on either product includes inhibitors. However the inhibitors are consumed over time and standard practice is to replace the fluid (replacing the anti-freeze in a car every few years for example). It is possible to replace the inhibitors but they are not widely available and it takes testing materials to determine appropriate replacement intervals and doses.

For a home heating system I would strongly recommend isolation of oxygen permeable tubing using a flat plate heat exchanger and replacing any ferric materials in the portion of the system that has the oxygen permeable tubing. If you want an additive for portions of the system containing ferric metals I would suggest a product like 8-Way™ http://www.rectorseal.com/index.php?site_id=1&product_id=172.