How to calculate the amount of glycol in my floor heat?

[Sequoia]

I'm inching forward with putting in a new boiler. One issue which has arisen is whether to evacuate and replace the 22 year old fluid and replace it with new. Recommended fluid is inhibited propylene glycol.

I have no records on the system, and the only thing I know is that there is about 1,000 sq ft of surface concrete. Is there a way to estimate how much glycol I will need? Some folks have guess at maybe 3 gallons or so?

 

[mjwalsh]

I'm inching forward with putting in a new boiler. One issue which has arisen is whether to evacuate and replace the 22 year old fluid and replace it with new. Recommended fluid is inhibited propylene glycol.

I have no records on the system, and the only thing I know is that there is about 1,000 sq ft of surface concrete. Is there a way to estimate how much glycol I will need? Some folks have guess at maybe 3 gallons or so?

Duane,

If it were mine I would look at the linear feet of tubing & calculate the volume by using my CAD program. It can also be done with a little math: inside area of a cross section of the tube times the inches will give you the volume which then can be converted to the ounces, quarts or gallons with numerous conversion tools on the internet. I actually did have a need to do that calculation several times over the years. I remember the original blueprint gallonage for our de icer system from RayPak was way underestimated. Here in North Dakota we need a minus 40 Fahrenheit mixture though.

A recent post covered hose volume calculations if that helps.

You may have to sketch some surpentine lines about 1 foot on center to each other if you have do not have a blueprint to work with. While the snow is melting it shows the basic outline of the tubing also.

Mike

 

[soapy]

You can buy a tester for glycol to see what freeze point it has. It is just like the ethyl glycol units that test your car antifreeze. Just be sure you get one for the type of glycol you are using. The testers are usually under $20. RV antifreeze is usually a 50/50 mixture good to -50 F.

 

[Sequoia]

Glycol

After some very very rough calculations, a few of us think we will need 3 gallons of glycol. I can add another 3 gallons of water to that and still maintain a 50/50 mix.

The glycol distributor said even a 30/70 mix would work to about zero degrees, but I don't want to skimp so I'll keep the mixture at 50/50 unless I need to cheat a little.

Gee, priced out the cost of a plumber lately? I thought I paid my software programmers handsomely .....

 

[mjwalsh]

Efficiency Consideration on Glycol Mix

After some very very rough calculations, a few of us think we will need 3 gallons of glycol. I can add another 3 gallons of water to that and still maintain a 50/50 mix.

The glycol distributor said even a 30/70 mix would work to about zero degrees, but I don't want to skimp so I'll keep the mixture at 50/50 unless I need to cheat a little.

Gee, priced out the cost of a plumber lately? I thought I paid my software programmers handsomely .....

Sequoia - Duane,

If it were mine, & I knew that the temperature never dropped below zero in our area I would dilute the glycol as much as possible because of the gain in efficiency. Most people are not aware that more glycol causes a loss of heat transfer with the same input BTU expenditure. I myself was surprised when I first saw a mechanical engineering trade journal article showing the proof etc. a few years ago.

Having said that make sure that you do not have any fresh water that can potentionally come into the system like a normal non antifreeze boiler system would have. Low water cutoff & flow switch alarming you & shutting off the boiler in a low water condition will make sure there is no danger of destroying your boiler. A sight glass is helpful --- so you know at a glance if your fluid is down slightly.

An RV might travel all over to even a minus 40 degree design area like here in North Dakota so there it would make sense as a precaution. I remember Herman Deal from Huron Valley showing me a map showing the different degree designs appropriate for different areas. Ours required a bigger boiler & the more concentrated amounts of glycol than most areas.

MJ - King Koin

 

[Sequoia]

Glycol

Good point. Unlike an RV, my concrete slabs won't do much traveling. It's 21 degrees this morning, actually pretty cold for here.

The "glycol man" said even a 30/70 mix would probably hold up to zero degrees, and considering heat transfer issues I think I will back it down from 50/50 to maybe 40/60 or something like that.

One problem I have had is that not many people in my area know how to do hydronics and boilers. But, I think the contractor I chose will do a good job. He's made all the right noises and asked all the right questions to tip me off that he is at least adequately knowledgeable.

Surprisingly, when I bought the "inhibited glycol" the chemical company gave me gallons of glycol and then gave me a quart of inhibitor-- so I could mix it myself. Hmm. I think the directions say 1-3 ounces per gallon for a cold water system, and double that for a hot water system. Regardless, I will have a LOT of this inhibitor left over.

 

[Dirtychuck]

You might want to go a little heavier on the glycol concentration just in case you develop a small fluid leak. Your boiler should have an auto fill valve to add water to the boiler if water/glycol level drops. If there is a leak and the fill valve starts adding water and glycol mix gets a little low it might cause some problems. I know this is a remote possibility, but this is what my floor heat installer recommended and it made sense when we were filling the system.

 

[I.B. Washincars]

I've never heard of having city water connected to a floor heating system. That sounds like a disaster coming at some time or another. An undetected leak could allow the glycol to get diluted to the point to where the floor would freeze...no way in hell would I have something like that. None of my washes have it and have never seen such a thing.

 

[Sequoia]

Glycol

It's been unusually cold here-- down to 15 degrees in the am. Of course, this is the time my floor heat decided to give it up.

We evacuated the old fluid from the system-- pumping it into 5 gal buckets. It promptly developed an ice layer on top, maybe 3/4 to an inch. I think it was straight water with no glycol.

I think I'll put in 40% glycol and 50% water. If it survived with NO glycol that should do pretty well I would think.

I'm glad I negotiated a "not to exceed" price. It's taking longer than they expected, why of course!

 

[I.B. Washincars]

I think I'll put in 40% glycol and 50% water.

What's the other 10% going to be?

 

[Sequoia]

%

Why, unpurged air, of course!

Make that 60% water.