I have a hot water boiler in a house that has a lot of air problems.

I have a hot water boiler in a house. The system has a lot of air problems. The circulator is on the return side of the boiler, and the compression tank is on the supply side — just like I find on most jobs. Part of the house is on a concrete slab, and there are pipes running under the floor. I’m going to shut down the automatic water feeder to see if we’re losing water. How long should I leave it off?

Dan replies: If there’s a leak under that slab you should see the pressure drop considerably within an hour. If you do have a leak, that would certainly explain the air problems. Cold water contains air. Heat the cold water and the air comes out of solution. The more leaks you have, the more air you have.

On this job, having the circulator on the return, pumping toward the compression tank isn’t helping you a bit. The circulator will drop its suction pressure whenever it starts, and that will just cause more air to come out of solution because of Henry’s Law. Add all this up and you wind up with a problem job.

Same Culprit, Different Victim

I bought my current home three years ago. It’s 23 years old with a gas-fired, hot water heating system. It’s a high ranch with three zones and one circulator. Since then, I have had nothing but problems, most of which center around having no heat in one zone. But sometimes there is insufficient heat throughout the whole house. The house will not get warmer than 63 degrees F when it is less than 20 degrees F outside. The no heat situation goes away when I bleed the baseboard convectors, but I could bleed these every day and still get air. By the way, the system has a bladder-type compression tank, which is set at 10 psi. I’ve had to raise the temperature of the water to 220 degrees F. My local heating person looked at the system in full operation during a cold spell and said the radiators may be undersized. He said I’d have to get a heat-loss analysis. He also told me I definitely need an air separator, such as the Spirovent.

What do you think? He suggested I could install the air separator myself since I’ve had experience replacing an entire hot water boiler. However, I don’t know which Spirovent to buy. Does it have to be installed on a horizontal run? Do I need a Spirotop? Is this the best solution? Please call me as soon as possible.

(I called and told him it sounded like he had a leak in the system. I advised him to shut the feed valve and watch the pressure gauge. Here’s what happened next.)

Sorry to bother you again. I ran that test you suggested. I shut off the feed water and watched for a pressure drop. The system failed the test. You were right when you said there was a leak in the pipe under the floor.

I’m reluctant to dig if there is any alternative because the floor is poured concrete and the pipe goes through a tiled bathroom and then into a bedroom with a glued-down, parquet wood floor. The burning question is this: Since this is a relatively slow leak, will a Spirovent be able to keep pace by removing enough air from the water that’s entering the system? Or will I have to dig up the floor?

Dan replies: I’m sorry to hear I was right. A Spirovent will take air out of the water, but that’s no cure for this problem. Since you’re heating all that fresh water, your fuel bills will be much higher than they should be. Another danger is the introduction of calcium and magnesium into the boiler when that fresh water flows through. This causes a condition known as “liming,” and that can clog the boiler, causing it to dry-fire. Dry-firing is what happens when the boiler runs with little or no water in it. It’s an extremely dangerous situation — one that can cause a fire or even an explosion.

In addition, the fresh oxygen that enters the boiler with the feed water will eat away at your boiler and cause it to fail. The leaking water might even undermine the foundation of the house. If I were you, I’d bite the bullet, find the leak and replace the pipe. It will never be less expensive than it is right now.

Good luck!

Yet Again!

I have a hot water boiler with three zone valves and a circulator on the return. The system has run for four years with no noticeable problems. Now, in the fifth year, there are all sorts of air noises. I keep changing the coin-type air vents, but the noise won’t go away. What do you think?

Dan replies: Here we have yet another leak in a buried pipe, right, dear reader? This is one of the reasons why I like to keep the automatic water feeder closed on hot water systems. I protect my boiler at home with a low-water cutoff. I have pipes buried under the floor, and I’ve had them leak. That’s why I don’t want that feeder open. I check my boiler once a week. I just walk past it and glance at the pressure gauge. It’s a habit. No big deal.

The Voice Of Experience

I enjoy your writing and turn to your section of PM as soon as it arrives. I knew the sort of plumber you spoke about in the August issue. Mine was the type of guy who could walk for blocks with a double-extra-heavy range boiler on his shoulders and install it on his way home. I think this was the same fellow who took the 5-foot cast-iron, leg-type tub up the stairs to the third floor without stopping. After he turned the tub over and crawled under it, he had me pass the handle of his claw hammer through the waste outlet so he could grab it from the inside. Then off he went up the stairs.

Now, I want to get to what prompted this letter. I have been winterizing summer homes in New England for a long time. This means homes with no occupants and no heat at all for the winter. I wish you would comment on the use of permanent automobile-type antifreeze used in residential, hydronic heating systems for winter protection. This is what I have been doing with no failures to date, even with subzero temperatures:

  • Test the job at 30 psi with cold water.
  • Increase the expansion tank’s size by 10 to 15 percent, or add another tank.
  • Remove all the supply connections by cutting the pipe. Use no automatic fill valve.
  • Drain the heating system and eyeball the volume of water.
  • At some high spot, dump in the antifreeze, equal to 50 percent of the water volume. Also, add some pump lubricant and conditioner.
  • Charge and purge the system with a garden hose at the boiler drain, with the circulators running.
  • We advise the homeowner that there can be no venting of the radiation. We also tell them to watch the system’s pressure gauge while the system is running. They should look for a rise in pressure. Should there be a leak in the tankless coil, there would be a pressure increase in the system.
  • We use a low-water cutoff to protect the boiler.

I did write to Prestone and asked how long their antifreeze would last in a closed heating system. They answered back with a three-page letter that I could not understand. I did gather that without new air coming into the system, the protection would last indefinitely. At least, this is what I wanted to hear.

I am here in Florida now. I gave away my snow shovel. I hope you will use this topic as a feature some time. It should be of interest to many. Thanks!

Dan replies: It took seven years, but I finally got to use that letter. I’d like you to contrast it with the advice my buddy Mark Eatherton, Colorado Madman, gave me when I asked him about winterizing radiant systems in the Rocky Mountains. This segment is from my book, Hydronic Radiant Heating — A Practical Guide For The Nonengineer Installer:

Mark Eatherton On Hydronic Antifreeze:

I think you should use glycol only when it’s absolutely necessary. The situations that warrant its use would be on snowmelt (pretty obvious, eh?) and in cases where the dwelling may be inaccessible for prolonged periods, or be subject to loss of thermal or electrical power. I would include any summer home in the hinterlands that uses propane for fuel, and where electric shortages and other unexpected situations occur regularly.

On snowmelt systems, we’ll usually use a 50/50 mix of glycol and water. At this ratio, the fluid has the consistency of diluted maple syrup with a nice purple color. Its capacity to carry heat is less at this ratio than it is with a higher proportion of water. You have to use larger circulators and bigger boilers. If you don’t, and if you’re using copper fin-tube boilers, the boiler’s heat exchanger will howl. Have you ever had a customer call and ask you if you’ve installed a ghost in their snowmelt system? I have!

The typical residential system will have a mixture containing 25–30 percent glycol. Some manufacturers recommend a minimum of 30 percent glycol to ensure corrosion inhibition, but bear in mind who’s selling you the glycol. It’s been my experience that in a good clean system, 25 percent works well. It will protect the heating system to around 15 degrees F for liquidity, and ten below zero for freeze/burst protection. I’ve checked all the systems that I’ve induced glycol into after two years and I’ve seen no appreciable degradation of the glycol’s corrosion-inhibitor levels. But then again, we take extra precautions to avoid using too much flux on our soldered joints. We also make great use of big bore PEX tubing for our distribution lines and that eliminates many soldered joints. You see, the acid residue from flux will overcome glycol’s corrosion inhibitors quite quickly — typically within a few years or so.

You should never connect an automatic water makeup to a snowmelt system because it’s liable to add water to the glycol mix and cause the system to freeze. If the designer or installer is uncomfortable installing a system without the feeder, he should use a low-system-pressure cutout to protect against dry-firing.

In situations where you have to use glycol, you should use only propylene glycol with a corrosion inhibitor, never ethylene glycol. Ethylene glycol is toxic to humans and animals, and it’s made from lightweight petroleum. PEX does not get along well with petroleum products. PEX manufacturers say ethylene glycol will make their tubing age at an accelerated pace.

The Uniform Mechanical and Plumbing Code requires the use of an approved backflow preventer to avoid the possible contamination of potable water resources. Although propylene glycol is a common substitute for sugar in processed foods, its sweetness will still rattle your teeth. I also recommend that you add a red dye to the glycol. That will give the homeowner a warm, fuzzy feeling when she sees a fluid on the floor that is not red. It’s probably just Fluffy the dog doing her thing.

There are two other things that will break down glycol pretty quickly — heat and oxygen. Heat, or what we call “pyrolization,” occurs at temperatures above 250 degrees F. My previous experience with solar systems that stagnate at 350 degrees F and higher has proven this is true, as far as I’m concerned.

Oxygen, which you’ll get in an open system such as you have with wood-fired boilers and solar systems, will cause the glycol to oxidize. Both of these conditions can create glycolic acid that basically eats copper for lunch. In most hydronic heating systems that are properly controlled, neither of these is of concern. In those situations where the water quality (well water?) is unknown or questionable, I’d recommend that you haul up some city water and use it for your glycol mix. Sulfites, sulfates, nitrites and nitrates can wreak havoc on water quality and pH balance and all of that comes with questionable water. If you’re not using glycol and the water is nasty, I recommend you use some other type of corrosion inhibitor. I like “Base Hit” from Hercules Chemical. It’s a combination of inhibitors, lubricants and sealants.

If you’re going to use glycol you’ll have to install a few extra piping components so you can get the fluid into the system. Typically, you’ll have a drain valve on either side of a ball valve and you’ll locate this on the main, preferably just upstream of the system circulator. With the ball valve closed, use a small submersible pump to move the fluid from the five-gallon mix bucket, into the drain valve that’s located between the closed ball valve and the system circulator. Pump the fluid through the system until it returns to the mixing bucket. You’ll premix the fluids in the bucket, of course. The inside of the bucket should have four marks — one each at 3, 4, 6 and 12 inches off the bottom. The marks represent 25 percent, 30 percent, 50 percent and full. Pretty simple, eh?

Although I’ve never seen any manufacturer’s recommendations on how often you should check the glycol, I think every homeowner should see a technically qualified, smiling face in his or her boiler room at least once a year — and not just to look at the glycol. It takes a spider just a few hours to construct a fine nest in the air inlet of a burner assembly. Once that happens, carbon monoxide production can’t be far behind. People need us, Dan.

Amen to that, Mark!