Antifreeze and System Capacity

Mark Mathys

Howdy,

I am considering adding antifreeze to my hot-water heating system. We commonly see -30F temps so I would like to have some freeze protection if the power goes out so I was thinking about protecting to around 0F.

I have a gas boiler in the basement and am installing a wood gasification boiler in the garage. I know the capacity of both boilers and know how to calculate the capacity of the piping. What I don't know, is how to determine the volume of the radiators. I have several different sized radiators, some about waist high and some about knee high. Is there a formula to determine the volume of the radiators based on their outside dimensions? Also any pros or cons to converting the system to antifreeze? I did read the info about antifreeze in the Hot Tech Topics.

Thanks
Mark

Al Letellier

anti-freeze

Mark, I'm not a big fan of anti-freeze in heating system, but here's what we do when we have to.....I don't have any formulas or capacity charts to those radiators, so we simply pump out the system contents into barrels to measure the actual system contents, then shed whatever amount we have to to get the proper mix and then pump it back into the system. You have to drain the system anyway, so this is the most exact way to do it.
Remember that a 50/50 mix will decrease your energy transfer to the water and you need to account for that (read the instructions with the anti-freeze). Also, the increased density of the water may require a larger expansion tank.
Installing the anti-freeze will require annual testing and making sure that the system is leak free. Good luck.

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Jack, CVMS

Mark,

Al has outlined a good, quick way of determining system capacity. It's what we use most of the time in a similar situation. Bear in mind you don't have to use a 50-50 mix. Where I live we don't consider it to be a real winter until the temperature has hit at least 40 below, but our standard mix is 35% PG. This gives a freeze (slushing) point of +4°F and burst protection of -60°F. It takes a long time for a structure to cool down that far, even at -50°F outside temperature.
If a section of pipe slushes up to where the circ pump can't move the fluid, 40 - 50 psi of air will usually move it, if things get that bad. But by that time you will probably be trying to drain all the domestic pipes anyway.

Mike T., Swampeast MO

Estimated Radiator Capacity

IN PINTS! AND PER SQUARE FOOT OF EDR!

Column rad: 1.5 Flue rad: 1.75 Thin-fin tube: 0.807

hr

I agree

30- 35% should be adequate. Buy a good brand, less expensive brands are pre diluted, and a much lower protection rate. Better name brands will have a higher grade and percentage of the inhibitors, such as ph buffers, O2 scavangers, etc. This is what you pay for with products like Dow HD glycols.

I would add to the above replys that a good cleaning is in order first. Buy a hydronic system flush product. Without a good clean system you risk ruinning the anti freeze inhibitor package right off the bat!

Keep an eye on any glycolled system. Make sure it doesn't take on fresh water, or you have wasted your time and money Best to install a LWC and disconnect the system from any domestic water fill valves!

You can buy or build feeders. www.axiomind.com makes small ones.

Also invest in test equipment or send a sample off for testing every year or so.

Glycol will last a long time if the inhibitor package is maintained. All manufactures sell "boost kits" to keep the fluid in spec.

Prepare for some leaks at threaded joints! Glycol is VERY slippery and seeps through the smallest of places.

I recomend it's use only when necessary.

hot rod

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ALH

Pre-mix

It's actually very easy to know what mixture you have. Drain the system and premix the propylene glycol and water before you pump it. When you drain keep track of how much you get out of the system so you know how much antifreeze to buy.

Mark Wolff

glycol mixing

Please DO NOT reuse the old water from your system, with all the rust and junk that always accumulates in a closed system. Measure the water removed, then mix new clean water with the glycol to the appropriate percentage. If you ever plan on vacationing or being out of the house more than two days, I would err on the side of safety, and mix a higher concentration than others posted. Also, remember that glycol's heat transfer rate is less than pure water. The transfer loss is perportional to the glycol mix percentage. Glycol is messy and will find leaks that you didn't know you had, but the peace of mind is quite nice. One of the last freeze-ups I went on had over 50 burst pipes, and a cracked boiler. Also, mechanical code requires some type of boiler makeup line, so either keep the backflow preventer and pressure reduction valve hooked up to the system and check system protection level every fall, or install a listed glycol reserve tank system.

Mark Wolff

Alaska

Where in Alaska are you located? Fairbanks area?

Jack, CVMS

Mark

In Glennallen. Lately we haven't been getting our usual winters. Only hit 30 below a couple of times last winter, and hasn't dropped below that yet this year - but it's clear tonight, and it was -30° this morning, so maybe it will get cold for a change.

Mark Wolff

Alaska

I'm in Kodiak, but we do a lot of bush jobs. Emmonak, Sheldon Point, Kotzebue, etc. etc. etc. Our weather is nice, in the 20's this morning, down from mid thirties yesterday. Maybe one day soon we'll see some snow.