There are two materials used for anti-freeze these days, ethylene
glycol, which is widely used in automotive applications, and propylene
glycol, which is sold for many marine applications.

Ethylene glycol is a little cheaper and more widely available. It is
poisonous to humans in large doses and to some animals in small doses.
On the other hand, propylene glycol is approved by the FDA as a food
additive and should be your choice for this use.

Either can be used as an antifreeze and coolant in engines, so
occasional heating in a hot water heater would be no problem at all.

Be careful to get the water heater actually filled with a mixture that
will freeze below -10F (for Boston) -- simply putting the freshwater
pump intake into a bucket filled with a -10F mixture and opening the
faucets one at a time might leave the water heater with mostly water
inside. Better to drain everything and then fill with -50F mixture.
This will cost a couple of bucks more, but what's a new water heater
worth?

Jim Woodward
www.mvFintry.com


(Richard Malcolm) wrote in message om...
I was planning to keep the boat in the water for a while up here in
Boston. I was thinking about draining all the fresh water out and
replacing it with anti freeze. either I am either too lazy or worried
that if I disconnect and bypass the hot water heater I will mees it
up. I am wondering if anything will happen to the antifreeze in the
next month or 2 if it gets heated by in the water heater. I am
planning not to do much at this time to the waste water sytem as I
like having some conforts.
What do you think? can I just put antifreeze in the fresh water sytem
or do I really need to disconnect the water heater from the loop?

thanks