Using anti freeze in a domestic central heating system

[Michael Chare]

Is it practical to put anti freeze in a domestic central heating system to stop the water freezing if the system is left switched off in the winter.

[Jabba]

Michael Chare wrote

[Harold Davis]

Michael Chare wrote in news: [e-mail]:

Yes - that's what they do in Sweden, using glycol.

Harry

[Brian Gaff]

Does seem odd to put in heating then turn it off when you most want it though. The only thing I have encountered is a neighbours evaporation thingy.. It probably has a name, which regularly gets stuffed up by ice and icicles hang from it. Then boiler complains and cuts out as I recall. Brian

[Reentrant]

There's nothing special about antifreeze. To a good approximation, depression of freezing point depends *only* on the concentration of additive, not what chemical it is.

Normal CH inhibitor would have pretty much the same effect mole-for-mole, and you need that anyway.

[Graham.]

Condensate drainage pipe.

[Dave Liquorice]

So the CH doesn't freeze but other water pipes do, hum...

Think you'd be better off spending the money on a frost stat.

[Capitol]

I'd have thought it was a waste of time unless you also drain down all the other water pipes in the house. You are likely to need up to 100L of antifreeze to do a house. Looks like up to £5 per litre.

[Andrew Gabriel]

You can buy combined inhibitor/antifreeze for this purpose (e.g. Sentinel X500), but it's not cheap because you need a much higher concentration than is required for standard inhibitor alone (typically, system needs to be something like 30% anti-freeze).

One of the former regulars here (Andy Hall) did this for a separate heating circuit which passed under his garden to heat his workshop. Because of the high cost of the antifreeze, he included provision to drain that circuit into a tank which allowed the antifreeze to be reloaded rather than lost.

As others have said, the heating system is only one type of water pipework which might freeze, and you will need to tackle the others someway too.

[Fredxxx]

On freezing a diluted mixture of antifreeze, instead of forming a solid lump of ice, what you get is more a slush, such that there is still considerable protection from split pipes and joints eased apart.

[Michael Chare]

I am looking for a solution for a holiday house. The advantage of antifreeze is that it will work even if the boiler fails to start. The other pipes would have to be drained off. Estimating the volume of the system is clearly the next problem.

In my presence house I do have a frost stat in the attic. Although this is set very low, it does sometimes trigger in the winter when the house is being lived in and heated. The house has to be heated quite hard to reverse the thermostat.

[Michael Chare]

Summer houses are very popular in Sweden and it gets very cold in winter.

[polygonum]

Really? No water from the mains to the boiler (or header tank if open system). Possibly not the best way of running a system.

[Lobster]

On 08 Sep 2014, Reentrant grunted:

I haven't a clue how much the freezing point can be depressed? Presumably a goodly amount since AFAIK it can protect a car radiator against anything the UK climate routinely throws at it; however it will be pretty concentrated in that application.

[polygonum]

In a roundabout way, I think we actually mostly do have a good idea of that. Might well have the story garbled, but I thought Fahrenheit put his best efforts into depressing freezing point with salt in order to set the zero point on his scale. Hence 0 F or about -18 C.

However it appears that ethylene glycol allows the temperature to get lower - around -40?

Not sure why this is - maybe how miscible/soluble the substances are in water.

[Grimly Curmudgeon]

Certainly. Use propylene glycol or even just glycerine if you know any biodiesel makers nearby.

[Onetap]

Yes; the Yanks do it frequently. Propylene glycol (non-toxic & maore expensive) not ethylene glycol (car ant i-freeze, very toxic).

You introduce a maintenance problem, in that the glycol turns into some a cidic compounds over time, in the presence of heat and oxygen (don't know t he chemistry). The acidic stuff will start really aggressive corrosion of t he radiators. You have to drain it & renew it before it turns bad, and moni tor its pH.

Plan B is a frost thermostat.

[Peter Hill]

On sealed system this isn't an issue, once the limited amount of oxygen is used it won't get any more and the inhibitor should cope with it, or have got first dibs on the oxygen.

With an open header tank there will always be a small amount of fresh oxygen being dissolved in the water.

Or plan C: leave the heating on with stat set to minimum. Not a good idea with a permanent pilot as the water from combustion can corrode the heat exchanger by condensing on the cold surface.

[RobertL]

IIRC he defined the freezing point of brine to be 0F, which fits with what you said. He defined 100F to be the temperature of a human. He got that s lightly wrong (we are 98.4F not 100F) because he based it on experiments wi th cows (assuming they were the same temperature as humans which they aren' t).

Robert

[Reentrant]

- about 6:25 in.