Hello, I'm in the process of building a floor heating system (well...not personally), and I already saw on many websites that it is recommended, in order to avoid freezing, to mix 50% water with 50% propylene glycol. But I was wondering, if propylene glycol is so good, why not fill the pipes with only that and no water at all? Does anyone of you know if this would do any damage or have some other drawbacks?
Any help is greatly appreciated :)

the more propylene glycol .the higher pumping cost. wear and tear even pump size

You want to run as little glycol as possible because it reduces the heat transfer properties of water. The higher the percentage of glycol in the system, the less efficient the system will be.

Anti-freeze in residential hydronic systems is almost always a bad idea for the reasons stated above. It must be properly specified and maintained annually by a competent professional.

Stay away from the websites that recommend it and avoid taking advice from your peers.

This is true for ethylene (?) glycol, the stuff for cars, and I suspect it applies to propylene, too. Your best protection (lowest freeze point) is w/ a 67% glycol/33% water mix. Not that your slab is going to get to -70 F or anything, but just for general knowledge I figured I'd throw in a car-related fact. Fair?

yep, thanks a lot everybody!

FYI in closed loop geothermal we use <25% in systems designed to operate wilth fluid temps below freezing.
To great a concentration would be similar to pumping honey.
J

Older thread, I know. But it fits with what I was thinking about.

What is the appropriate mix for a situation where you would have a slab siting cold for weeks or months at a time, and the winter temps can drop to - 40 or -45 celcius?

Looking at building a cottage for the wife, but I would need to deal with the frigid Manitoba winters.

Here in Minnesnowta, we use Cryo-Tek 100.  This is a tubing anti-freeze designed for closed loop systems.  In cold climate situations (Minnefroza) we need the anti-freeze in the loop to prevent freeze ups due to a possible garage door that stayed open or if we have a storm that knocks out the electricity.  We have temps down to -30 and windchills to -50 to -60 at times.  We have to plan for the worst case and use a factor of 1 gallon of Cryo-Tek to 100' of infloor tubing.  What is the worst of 2 evils, loosing a little efficiency to the anti-freeze or have a system freeze up?

You'd need about 55 % of propylene glycol to protect to -40 which would be pretty high viscosity. If you really expect the house to hit -40 inside you maybe should not choose radiant heat.

Radiant's strength is not in occassional use anyway. Even in much milder conditions it would take quite a bit of time to heat up the house every time you arrived. Save some money and put in electric baseboards. Much cheaper to install up front and faster warmup. Might cost a little bit more than gas to operate but probably not enough that you'd ever come close to the extra up front costs of a gas radiant system for an ocassionally used vacation house.

you can fairly easily add a phone switch to heat the place up before you get there, which if it's only a few times a winter would not represent a gigantic fuel costs. it would undoubtedly be more comfortable as well than having a stone cold slab with electric baseboards for heat.

it's not about fuel usage, it's about comfort, in a vacation home.

Setting a room or slab thermostat to 35 F to keep the heating system from freezing up doesn't seem like rocket science. It has to be wicked-cold for quite some time for the heat load at interior temps of 35F to add up to much. (Or is this somewhere you expect the power to go down and stay out for weeks on end when it's under 10F out?)

With a sharp pencil you can determine the cost/benefit crossover of the upfront cost & lifespan of the glycol & efficiency loss incurred against the cost of burning fuel as freeze protection, with higher operational efficiency. Harder to determine would be the risk/costs of damage to the system from cooked glycol from lack of maintenance against risk of freeze-up damage in a particular situation. (If it's heated space, occupied at a high percentage of the time, unless you're using it to keep the snow & ice of the patio in -25F weather, skip the glycol.)

Setting a room or slab thermostat to 35 F to keep the heating system from freezing up doesn't seem like rocket science. It has to be wicked-cold for quite some time for the heat load at interior temps of 35F to add up to much. (Or is this somewhere you expect the power to go down and stay out for weeks on end when it's under 10F out?)

With a sharp pencil you can determine the cost/benefit crossover of the upfront cost & lifespan of the glycol & efficiency loss incurred against the cost of burning fuel as freeze protection, with higher operational efficiency. Harder to determine would be the risk/costs of damage to the system from cooked glycol from lack of maintenance against risk of freeze-up damage in a particular situation. (If it's heated space, occupied at a high percentage of the time, unless you're using it to keep the snow & ice of the patio in -25F weather, skip the glycol.)

any significantly unoccupied house cannot rely on a thermostat alone to prevent freezing, especially at something like 35 degrees which leaves no wiggle room in the event of a failure.

That is a glycol-required situation. Risks are far too high of a freeze up in that case. I would say that for any unoccupied building.

We used a 50/50 propylene glycol mix in a hot-water baseboard system for years trouble-free. Using this mix actually increases the latent heat of the solution and moves a significantly higher amount of BTUs through the system than plain water. Here in SW West Virginia we do have long power outages at below zero temps, and it will destroy your entire heating plant in just a few hours. Happened to me, that's why it's treated now. The difference in BTU movement was immediate and obvious, as the house got warmer.

It was a rehabbed older house with leakage problems, so keeping it hot below zero was a problem sometimes.

We got food-grade PG from a local dairy that uses it in their chiller equipment to maximize the movement of heat (cool) in their system. This was a copper baseboard system, but my nieghbors with a radiant floor used the same mix.

Thank you Larry, how refreshing to hear an educated voice (other than Rob and Dana of course :).

The rest are old women over their tea.

Can you say Freeze Alarms?

Easy, reliable and won't compromise every aspect of your heating system, from the heat transfer rate "specific heat" to the higher viscosity which will raise the - totally parasitic - circulator operating cost by as much as 10%.

One more radiant floor heating myth dispelled: You can heat your cabin from afar as Rob points out and the reponse time is dependent on many factors including the type of panel, tube depth, floor covering, heat load AND heat medium, since glycol will slow the response time of any hydronic heating system.


Unless I missed it, no one has addressed the difference between freeze and burst protection. As I design and install a number of snowmelt systems every year, the distinction comes up. Freezing in most PEX systems simply doesn't matter, no burst. A 50/50 mix of glycol for residential heating systems in overkill until you reach the artic circle, as the "burst" temperature is some where around -60°. I typically use a 40% mix for snowmelting and need flow down to 0° on Class 1 residential designs. Our mean extreme here in Minneapolis is -20°F.

There is nothing good about glycol short of protecting neglected heating systems from freezing. I have taken more out this year than I put in and the majority of it was sour, not protecting but neglected and actually eating the system components. False sense of security comes to mind.

More than a 50% mix by the way "lowers" the freeze protection!

When designing home heating systems for remote locations I often specify a non-electric gas-fired fireplace. It takes so little to keep a home from freezing with a little forethought. When they do freeze up people call their insurance man. Paying to maintain and operate a propylene glycol filled heating system is like buying insurance TWICE. But hey, my grandfather wore a belt AND suspenders.

Much information is available from the manufacturers though it can be confusing without a bit of study time. I always use a refractometer to prove the mix and then don't have to use the tried-and-true one bucket of glycol to one bucket of water mix like grandpa did. Incidentallly water quality will effect the quality and "protection" of any propylene glycol mix.

If a cabin is rarely used in winter the point is mute as is should be winterized.

I keep my own place at 50 and turn it up the night before I arrive.

Badger,

Good points on a freeze alarm.  Would be very simple.  I should have thought of that!  And good to understand about freeze and burst.  Really needed to think about it anyway for the potable water supply.  I wondered if PEX would stretch enough to keep from bursting.  Obviously it does. 

What about micobial growth?  What is normally done to keep that under control?

PEX is hard to freeze to burst unless it in bound it cement or Gypcrete! When bound it will find an air pocket and blow a plug out. This is too common when folks (both the novice and the professional) use a hydrostatic test instead of a more-than-suitable air test and then forget that cold weather might come before the boiler. A properly vented hydronic system will naturally be purged of oxygen the first season...no worries. Though anaerobic bacteria exist, few residential systems suffer from them.

For a garage in MN, I know a couple of you are from the Minneapolis area, what % glycol should we run? I want to run the minimum with out worry of a break. The garage may never freeze, even if the heat goes out, but it is a new system and we don't know that.