why drain/refill hot water heating system

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Old 11-23-10, 01:44 PM
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why drain/refill hot water heating system

I was just advised by an HVAC person than my hot water boiler heating system should be drained and refilled and air purged at least twice a year. I do not understand why. It originally had glycol in the system and still has some (much has been replaced with makeup water as parts were replaced over the last 4 years). I do not hear any air in the zones as they operate and the Taco air vent or separator seems to work, meaning it is not leaking and not corroded. All zones seem to heat properly. Is this a normal maintenance procedure?
 
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Old 11-23-10, 02:05 PM
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Is this a normal maintenance procedure?
Absolutely, positively NOT !

That information is totally WRONG.

Doing so will absolutely result in greatly increased corrosion of the boiler and associated ferrous parts.

Once all the oxygen is driven out of the initial fill of water, that water should remain in the system as long as possible. Once the oxygen is driven out, that water becomes INERT and will not cause corrosion of the system.

Whereinhell would he get such an idea?
Let me guess, 'wet behind the ears?'
 
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Old 11-23-10, 02:46 PM
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Thanks for confirming what I suspected. The boiler operates all year for DHW and heat for 8 months+/-. The flame looks good, no black or sooty tips. There does not seem to be a accumulation on the bottom of the heat exchanger. The floor below the burner is pretty clean. Expansion tank is not water logged and the water pressure per the combo temp/pressure gauge stays at about 15#. This gauge was replaced a year ago. What other maintenance is suggested?
 
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Old 11-23-10, 03:32 PM
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Is the boiler Gas or Oil fired?
 
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Old 11-23-10, 04:01 PM
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It is natural gas. It is a Teledyne Lars tankless boiler about 15 years old.
 
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Old 11-23-10, 04:48 PM
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What do you mean by 'tankless' ?

That's a copper tube heat exchanger boiler design. They are very sensitive to flow across that heat exchanger. Do you know if your system is piped with a BYPASS ? It should be in order to protect the boiler.

One thing that is sometimes problematic with those boilers is that the heat exchangers do tend to get 'limed up' over time, ESPECIALLY if the flow is not right. And the fire side of the heat exchanger can get plugged also, mostly due to flue gas condensation issues causing corrosion. This is also often because the proper bypass hasn't been installed, and the water returning to the boiler is cool enough to cause the flue gases to condense. Since the flue gas condensate is mildly acidic, it can corrode and eat away at the copper.
 
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Old 12-03-10, 10:45 AM
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Sorry for the long delay in responding. Hope you are still monitoring. Okay tankless was the wrong term. Yes, the system has a bypass. The bypass valve is adjusted to where there is a maximum temp drop of 20 degrees between input and output. Does the presence of glycol have any effect on the liming/coating of the exchanger? Also, this has an induced draft exhaust. System is at high altitude (8500') and characteristically low humidity (<15%). Maybe these factors help lessen the exhaust gas damage. ??
 
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Old 12-03-10, 03:34 PM
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No problem, I ain't goin' anywhere soon I hope!

I'm no expert on glycol fill... but logic would say that it might help prevent it... but that is just a wild a55 guess. What probably SHOULD be done though is to have the PH of the glycol tested from time to time to make sure it doesn't become acidic.

Maybe THAT is what the tech was thinking? Ya know how they tell you to change the antifreeze in yer car periodically? In any case though, TWICE A YEAR is nutz... I would think that if the PH were checked yearly you would be OK.

I think our friend Furd is probably the best informed on boiler additives, maybe he will jump in and advise.

Dry air might make an ever so slight difference in the condensation issue, but the fact is that the water vapors that can condense inside the boiler are not the water vapors in the air. Instead, it is the water vapor that is formed from the combustion process of Hydrocarbon based fuel. A chemical reaction. The combustion process breaks up the hydrocarbon chains and they recombine into various compounds, water being one of them. In gas fired combustion, the 'dew point' of the flue gases is about 132, so if those exhaust gases come in contact with anything colder than that, condensation will occur.

As for routine maintenance of your boiler, it sounds as though you are pretty much doing what you should be... keep it clean, inspect occasionally for 'crud' in the heat exchanger and flue pipes, brush and vacuum as necessary. Keep an occasional eye on the pressure gauge. Always be alert for any new or unusual sounds, that kind of stuff... but:

There is one sadly neglected component in all heating systems. The Expansion Tank.

Under normal operating conditions, a bladder type tank loses something like 1-2 PSI of it's air charge per year. I always recommend that the tank be checked a MINIMUM of every two years for the correct air charge. Once a year is better.

It's not quite as easy as putting a tire gauge on it though... because as long as there is pressure in the boiler, you will NOT get an accurate reading. You have to drain ONLY ENOUGH water from the boiler (after shutting off the water supply of course) to drop the boiler pressure to ZERO. Only then can you get an accurate reading of the tank charge. If found to be below 12 PSI, add air with a small compressor or bicycle pump until you have 12-15 PSI in the tank. Check the boiler gauge again. If it has risen from zero, drain a little more water to get it back to zero. Check the tank charge again. Repeat these steps until the boiler stays at ZERO, and the tank is at 12-15 PSI.

Other than that, sit back, relax, and enjoy an adult beverage!
 
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Old 12-03-10, 10:14 PM
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I would avoid the use of a glycol (specifically propylene glycol) additive unless you have a frequent problem of power outages during freezing temperatures. If you do need the freeze protection then you need to use an "inhibited" product, a propylene glycol that has a corrosion inhibitor added by the manufacturer OR add your own corrosion inhibitor. If you do use the glycol then you MUST do periodic testing to ensure both the freeze protection AND the level of corrosion inhibitor in addition to pH testing.

For "yellow metal" (copper, brass and bronze) protection you need a corrosion inhibitor with tolytriazole and to protect the steel and iron components you are best with a molybdenum / nitrite compound. These are difficult for a homeowner to find and they do require test equipment to ensure the proper usage. For most systems drinking quality water is just fine IF the water is not changed too often. Softened water is better than hard water.

For periodic maintenance Trooper forgot to mention changing the safety valve every five years.
 
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Old 12-08-10, 01:02 PM
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glycol in hot water boiler heating system

I do not know the specifics for the ingredients in the glycol. It was put in by a plumber who added two zones to the system. I remember the bucket label said it was for hot water boiler systems. The reason for the glycol was because the new zones were added in a portion of the house that is built about 5 feet above ground without a basement beneath. It is built on piers. The pipes go between the floor joists. There is R30 fiberglass insulation between the joists and 1.5" of rigid (R7.5) pink Styrofoam type below that. This section of the house has the hot water baseboard heat installed but seldom used. The room is heated with a natural gas Hearthstone stove. The concern was that the water within this section might freeze due to not being circulated. In the 3 years since installation the glycol has been mostly diluted out as repairs etc. have required partial draining and further dilution. The system has worked fine and the elevated and unused zone has not frozen. It has been below zero several times. I would prefer to not replace the glycol as I understand that the glycol reduces the efficiency somewhat. At present the boiler is undersized and I am trying to get all the performance I can from the boiler. This is why we don't use the zones where the Hearthstone is able to provide the heat. However, if you say the loss of efficiency is not significant and the glycol and additives are beneficial, then I will drain and refill with new glycol. Is there a specific brand product that provides the glycol and other additives you can recommend?


Thanks for all your help, NJTrooper and Furd.
 
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Old 12-08-10, 04:35 PM
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With glycol, you either want a full proper mix between 30 to 50% or nutting at all.
Low percentage mixes have been known to grow bad things in them causes a sludge to develop in the pipework.
Propylene glycol is plant based and therefore organic, and can get rather nasty if the PH and additives go off.

Best have it checked, and if it's getting low flush it out.
 
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Old 12-08-10, 04:55 PM
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Personally, I think a hydronic system is not a good idea for a space that is frequently unheated. But I realize that advice comes a little late.

Here are a couple of alternatives to consider. Use a heat exchanger and put the unheated spaces on a secondary loop. Put antifreeze only in the secondary loop and leave it out of the rest of the system.

Since you have good insulation in the joist space with the hot-water piping, you could add electric heat tracing and maybe not use too much electric energy.

Do you have zone valves? You could put a minimum-flow bypass around the zone valve for the unheated area - just enough flow to keep the lines from freezing.

Or just turn up the thermostat for the space to a minimum temp.

Install drain valves and drain the unheated system except when you want to heat it.

Any idea other than antifreeze is worth seriously considering.
 
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Old 12-08-10, 05:44 PM
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If the pipes are between the insulation on the living space, I don't think I woujld be too concerned about them freezing because they are being kept warm by the heat of the home.
 
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Old 12-08-10, 06:31 PM
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I was trying to explain that it appears the glycol is not necessary as we have had several days below zero without problems. I was willing to refresh the now heavily diluted glycol if it would be considered beneficial for the other additives that Furd was speaking of. And, admittedly, even though it has not frozen, I do feel better when it is there. We did have a 10 day power outage after a heavy wet late spring storm two years ago. If this happened in the coldest part of winter then only glycol would save the system.
 
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Old 12-08-10, 09:03 PM
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You don't need to use a glycol solution in order to get corrosion preventive but it may be the easiest method. If you do want to use propylene glycol then you really should have some testing equipment.

The first is a refractometer to measure the actual freezing point of the liquid. This unit is about $50 and can also work with the ethylene glycol used for automobile antifreeze and also for determining the specific gravity of a lead-acid battery electrolyte. Here is one example. Refractometer

The next thing you need is a method to determine the pH (hydrogen ion concentration) of the liquid. The easiest and cheapest method is by using pHydrion test tape which you might be able to buy at a pool supply store. The liquid needs to be kept at a pH of 9 to 11 to prevent any kind of acidic corrosion.

If you can find some place to buy small quantities of a molybdate / nitrite corrosion preventative then you will need a nitrite test kit. For this last I recommend that you check around for a small steam or hot-water heating facility such as a neighborhood school or a commercial laundry. Talk to the operating engineer and find out when the water treatment consultant comes by (usually once a month) and then talk to the consultant about your system. If you work for a large company that has an on-site boiler plant then this may be easier. Explain what you have for equipment and see what the consultant recommends. If it is a compound that is used in the plant then you can see if the engineer is willing to sell you a small amount for your use and also will do the testing. You only need small amounts of treatment depending on the size of your system and the strength of the treatment compound. I used different products from different companies and for the system I was treating it amounted to maybe a cup or two a year.

There are some companies that sell generic boiler chemicals over the Internet but I have no experience with them nor do I know what they contain. The local water treatment consultant is your best bet for information but it is doubtful he will be a source for the chemicals in the tiny amounts you will need. If you have neighbors that have hot-water heating systems AND are DIY types you may be able to pool your resources and buy chemical in five-gallon buckets from the consultant. Understand that it won't be inexpensive, the last price I had on Nalco Chemical Company product 2833 (which is what I would recommend for any hot-water heating system) was about $36 a gallon when purchased in 55 gallon lots. Buying in smaller quantities raises the price per unit so you can see if you can sweet talk the operating engineer in a small plant into selling you (or perhaps trading some other liquid of value )it will definitely be worth your while in making a new friend.
 
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Old 12-09-10, 10:37 AM
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does the glycol lessen efficiency

Wow, that is a lot of detail. I am likely to simply go with a glycol solution that includes the proper anti corrosives. Is there a brand that you suggest? Otherwise the idea of all the additives and the sleuthing for a supplier is more than I want to get into. Is the heat transfer efficiency reduction significant with glycol compared to just water? As stated before, I am using an undersized boiler as is. Actually, I need to start another thread and ask how to tell when I am indeed undersized? Boiler that is... I can't keep the house up to temp when it is below zero. Is there an existing thread on this?
 
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Old 12-09-10, 02:31 PM
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My experience is glycol is no good. To me and from what I have seen its very corrosive. I dont care what you add to it. Disadvantages out way the advantages. I have seen new boilers crude up bad with this stuff. If water moves it will not freeze. And thats what a boiler does is move water.

Advantages

It acts as a freezing point depressant which of course is why it is being considered as a boiler fluid. In cold winter weather ethylene glycol will turn to sludge rather than ice, and reduce the risk of bursting pipes .
It acts as a lubricant: it will keep your pumps and plumbing moving.
low viscosity, so it doesn't take a mamoth pump to push the fluid through the piping of your outdoor wood furnace.
A Solvent: it mixes easily with a number of other chemicals that are critical to inhibiting corrosion and sludging in antifreeze formulations designed for home boilers....


Disadvantages

Ethylene Glycol Poisoning: ethylene is an odorless and colourless sweet tasting liquid that tends to attract animals, especially dogs that lap up spills and puddles that are left standing. It can contaminate potable water and come in contact with unsuspecting humans... It is considered a hazardous waste according to the EPA.....

Some jurisdictions are now taking this to the extent of forcing manufacturers to dope ethylene glycol with bad tasting chemicals to deter pets and children from ingesting this liquid.

This is a serious poison. It forms calcium oxalate crystals in the kidneys and can cause acute renal failure and worse!


Ethylene has an oil base: this can shorten the life of some HVAC tubing. Be sure to ask at the time of installation. Plumbing that is encased in the cement under a slab is next to impossible to replace if the plastic gets pitted by anything that runs through it.
Stratification: When diluted with water, ethylene antifreeze will stratify and leave almost pure water on top that freezes and pure ethylene on the bottom that doesn't. Often the answer has been found by mixing methanol and Ethylene glycol to create a soluble product that will mix well with water.

This is the formula most commonly found in automotive antifreeze, windshield wiper fluid and de-icing chemicals... although there is a transition towards propylene, but cost IS an issue.
Uninhibited glycol can cause extensive corrosion to metal boilers if appropriate chemicals are not added to the mix.
 
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Old 12-09-10, 03:47 PM
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I agree with Lawrosa that it is best to not run any kind of glycol solution in your residential heating system but if you must to protect against freezing then the ONLY kind is propylene glycol. Ethylene glycol is a deadly poison whereas propylene glycol is used in certain foodstuffs.

You also MUST have a backflow preventer on the make-up water piping when using any chemical treatment, including propylene glycol. I personally prefer to keep the make-up water valve closed when using any chemical treatment and a water meter is a desirable addition and can help in determining the amount of chemical to be used. The refractometer I mentioned previously is invaluable in determining the freezing point of the boiler water/glycol mixture, I wouldn't use any glycol without having my own means of determining the freeze point. Without the knowledge of the freeze point you will either under treat or over treat.

The pHydrion test paper is also an absolute must because the corrosion inhibitors WILL be depleted over time without any change in the freeze point. When the corrosion inhibitor is completely depleted AND / OR the glycol starts to break down the system will turn acid VERY quickly and the corrosion will start destroying your system rapidly. Because the corrosion inhibitor will become depleted BEFORE the system turns acid it is best to test the system for active corrosion inhibitor BEFORE it is depleted and add more as necessary.

I can't make any recommendations of chemicals or suppliers for residential systems beyond what I have already written because my experience is with commercial and industrial sized equipment. There are companies that cater to the residential sector but I have no personal knowledge of their products.
 
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Old 12-09-10, 04:34 PM
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Your 15-year-old boiler is undersized - caused by or made worse by the addition to the house which is frequently unheated (also resulting in the need for antifreeze).

Here is an idea that may sound drastic, but probably no more so than using antifreeze in your system. Rip out or cap off the hydronic heat in the space that is frequently unheated. Replace with electric baseboards.
 
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