Posted By jojojo on 22 Apr 2014 10:43 PM
Okay....so am I safe in thinking that since we can/have lost power for long periods of time (24-72hrs) during winter storms...then my system is at risk for freezing and I should be using antifreeze in my system...

Thanks again
jolene

Jolene - if your basement is in the ground on all sides by 4 to 5 feet, it is unlikely that you will be at risk of freezing unless you had an extended cold snap and power out at the same time. At your design temps, you should not have a problem going 4 to 6 days without power. Maybe a little less if you have insulation under the slab. The rest of your plumbing would be at greater risk. My comments on the need for antifreeze are based on a walkout scenario where the slab is right next to an exposed concrete wall which would not be the case if the basement is buried on all sides.

FBBP-sounds like that is similar to my situation! The complete back is walkout/ground level as well as 3/4 of another side ...My basement would only be buried on 2 1/4 side. And I know there is insulation below the slab.

I guess we never worried about freezing before the new water heater was installed as the system was installed with antifreeze. No new antifreeze was added when system was refilled.


Decisions...decisions...decisions!

Thanks again
jolene

Jolene, if the ground in the vicinity of all portions of your slab always stays well above 32F, you do not need to use antifreeze. This is typically the case for full basement slabs if all the slab area is located well below the frost line for your area. If you obtain a cheap hand IR temp gun (i.e., from Harbor Freight, etc.), you can shoot your slab temps the next time you lose power for an extended time. It will likely be in the 45-55F range year-round in the below ground sections, but will likely reach freezing temp in the walkout section. If your HR control system is not properly monitoring slab temp and you are at risk of losing power for extended periods, you should use antifreeze. Gayle

Gayle -thanks for the suggestion...I will get a temp gun and check temps next winter before making any changes with the system...besides turning off the water heater for the off season that I will do!

Thanks for your answers and patience during my learning process!!

jolene

Jolene to make the decision examine the risk.
Where the basement is not protected by insulating earth or other insulation, how much of the wall is exposed to the weather?
Is this wall a standard 8" cast in place concrete wall?
Is there any insulation between the basement slab and this outside wall?

If there is insulation between the slab and the wall, your risk goes way down as the residual heat of the slab will not drain into the outside concrete wall while the hydronic heating is in its off cycle. On the other hand, if your floor slab is pour right against the exposed concrete wall, the heat in the slab will bleed quite quickly. After a week of minus 18 (0ºF) the concrete wall will be close to that same temperature. The chances of the basement heat cycling fast enough to prevent the water in the tube next to this wall from freezing is low especially if there is a loop that runs parallel to the exposed wall.
Since this is just a hydronic system run off a water heater, it is unlikely that you have any type of slab sensing thermostat. Even if you do, the sensor is probably place in the slab near the thermostat, in the middle of the room, so it is unlikely that it would trigger a new cycle in time to prevent the outside loop from freezing.
You have indicated that you have a geo thermal unit which I assume heats forced air as you are using the water heater to heat the floor. So likely you have a few vents from the forced air dumping into the basement. If this is the case, it will further lengthen the time between cycles and increase the freezing risk.

As you have indicated that there is insulation under the slab, ground temperatures have little impact on how the slab losses heat.

In summary, if there is a couple of inches of foam insulation between the wall and the slab, such that it is an extension of the underslab insulation, you have little risk. Check the area of the door as well as often the slab itself extends out under the door to the outside.

Reminds me of client that called from Texas. When I asked about insulation under the slab he laughed and pointed out that it never freezes in Austin.


I have warm memories of Calgary...none of them are from he outdoors...

In some of our solar designs PV panels power small circulators, moving water tends not to get solid.

We reserve slab sensors for commercial or extraordinary residential applications, since (like suspending PEX in a basement slab) they add an unnecessary level of cost and complexity.

“In summary, if there is a couple of inches of foam insulation between the wall and the slab, such that it is an extension of the underslab insulation, you have little risk.”

Not true, slab insulation only SLOWS the rate at which the slab will reach the ground temp…the slab will still reach the ground temp… If the ground temp is at or below freezing temp and you don't have power to operate the HR system, an insulated slab will still reach that freezing temp and you are at high risk of freezing the PEX if antifreeze was not used and you are also at increased risk of damaging the PEX if it was not fully encased in the reinforced concrete slab.

We figure the extra $10 in cost to have slab temp monitoring is an acceptable tradeoff for assured freeze protection and increased operational efficiency for the lifetime of our HR systems. Placing the PEX in the middle of the slab only requires competence/skill and there isn’t any increased cost or complexity for us…just additional increased operational efficiency for our customers, both commercial and residential.

Looking at my freezing probability.....and to answer a couple questions.
*My house does NOT have insulation between slab and outer wall.
*Where the earth is not insulating my walls, they are ,100% exposed to the weather.
*My house does NOT have slab sensing thermostat/or sensor monitoring....(wish it did).
*I do have geothermal heat with heat ducts dumping forced air into the basement.
*basement is 100% finished ...90% pad n carpet...10% ceramic tile.
*the PEX is in the middle of the slab...and no lines were ran any closer than 12" next to any outside walls.
*usual temperature/setting is 68°...anything higher makes it to warm.

So if I feel my freezing risk is elevated and I should be using antifreeze....... Should we drain system and start over so we know amount or percentage of antifreeze in system? Or is there a better way to check amount? (A tool like we test our car antifreeze with???)

Thanks again for some more great pointers/tips that I did not even figure into the antifreeze equation!!

jolene

As I previously suggested, if you are at risk of freezing any section of your slab, you should use antifreeze. Your multi-day power outages, your walk out basement, and your less than desired insulation puts you at risk of freezing. You also indicated that your system previously used antifreeze. So YES, we would recommend that you continue to use antifreeze.

Only propylene glycol should be used to protect a HR system from freezing…never use ethylene glycol. It is often recommended to use at least a 30% propylene glycol concentration to inhibit the growth of bacteria in the system. Yes, there is a device similar to what is used to check car ethylene glycol concentration level that you can use to check propylene glycol concentration level.

Borst....great to know there is a tool to check concentration levels of propylene glycol levels also! That's what we will purchase to check the levels.

Thanks for all the information
Jolene