Anti freeze in gas hot water heater??

[Jaggy Taggy]

I have pipes in the floor of a new building and I am thinking of heating the
water (rather water-antifreeze) mix with a regular gas fired hot water tank.
Of course I could never use that old water heater for potable water again,
but that doesn't matter, I have an entirely different system for that
purpose.

The question I have is if the anti freeze would somehow break down during
this usage, being exposed to very hot temperatures at the heated surface of
the tank (but probably not much different from the temps inside a car
engine).

Has anyone around here experience with this, is there any reason not to do
this??

Uwe

 

[SQLit]

I have pipes in the floor of a new building and I am thinking of heating the
water (rather water-antifreeze) mix with a regular gas fired hot water tank.
Of course I could never use that old water heater for potable water again,
but that doesn't matter, I have an entirely different system for that
purpose.

The question I have is if the anti freeze would somehow break down during
this usage, being exposed to very hot temperatures at the heated surface of
the tank (but probably not much different from the temps inside a car
engine).

Has anyone around here experience with this, is there any reason not to do
this??

Uwe

If the area is above freezing what do you need the anti freeze for?

Water treatment for minerals would be what I would consider.

 

[Bughunter]

Yes, it breaks down over time and you will need to replace it periodically.

I have anti-freeze in my boiler that uses hydronic baseboard type radiators.
Building codes in my area dictate that this must be a non-toxic antifreeze,
and not toxic automotive type anti-freeze. Also, a system is present to
remove air bubbles ( a scoop, with air escape valve), an expansion tank, and
a special one way mixing valve to allow water to automatically be added to
the system as some of the fluid gets lost over time. That has a tendency to
dilute the anti-freeze over time. Periodic checks for anti-freeze
effectiveness is warranted. The reason that non-toxic is required by code is
to keep the system from contaminating potable water in the unlikely event of
a failure in the one way mixing valve from the potable water supply. In a
completely closed system, not connected in any way to a potable system, it
may not be necessary. But, you may want to ask a code enforcement official
to be on the safe side.

This is all pretty standard stuff on heating system boilers, especially in
the north east US where a power outage could cause you loose heat and risk
the possibility of freezing part of your hydronic heating system.

If you are thinking of using a hot water tank, I can't think of any reason
it would not work. The downside is that you will have lots of excess storage
in the tank, and the antifreeze is expensive. Also, a most tanks designed
for domestic hot water do not have sufficient recovery rate. A better
solution would be a higher capacity tankless type heater. They make some
that are sized to perform whole house hydronic heating.

 

[clare at snyder.on.ca]

If the area is above freezing what do you need the anti freeze for?

Water treatment for minerals would be what I would consider.

It's been done - usually using Propylene Glycol. You need an air
bladder, like a "wel-trol" tank to maintain pressure and keep air out
of the system.And you need the normal circulating pump.

However, most domestic boilers are higher efficiency than the water
heater.

 

[Jaggy Taggy]

Well Bughunter, I am in the woods of Maine, the house to be heated is well
insulated and I thought of this gas hot water heater is because of its low
output (35K BTU). I need less than that to heat the place.
I don't have to worry about building code.

I use tankless water heaters for other buildings etc, but what do I do with
125K BTU??
Also, I use hot water solar panels on the roof and tying it all together is
the challenge. Heat exchangers are difficult and I would need to run a bunch
of pumps for the various loops, so an exchange-less system where the solar
panels heat some water in the boiler and if it is not heated enough the gas
kicks in seemed like a good idea, but I wasn't sure about the antifreeze as
I mentioned in my earlier post.


But input from anyone who has actually built such a thing is appreciated.

Uwe

 

[Gordon Richmond]

I have a 2-car garage that is heated in exactly this fashion.
DHW heater coupled to hydronic floor heating. There IS an expansion
tank and a circulating pump. There is no valve to admit water from the
water system.

The garage was built in '92, and I bought the place in '98. AFAIK, the
system has been trouble-free over that period. Honestly I don't know
what flavor of glycol is in there, propylene or ethylene. There's
never been any drippage from the relief valve.

Apparently, this installation met code at the time it was installed,
but code now prohibits this use of a DHW heater; around here (Alberta)
at least.

It certainly does work, but it may be less efficient than a
pupose-built heating boiler.

Gordon Richmond

 

[Bughunter]

Even if you are not subject to building codes, it is still not a bad idea to
understand them because they are often enacted for reasons of safety for you
and your family. I'm in "Live Free or Die" state of NH, in a town without
building codes, but there are still state codes.

If it were me, I would use a non-toxic anti-freeze such as those for home
boilers. It is probably less expensive than toxic automotive anti-freeze and
I would assume just as effective. If you are fortunate enough to lie in an
area without codes, then you can do whatever you please.

Too many btus are better than too few. You can always put a thermostatic
control in place to shut off the heater whenever the room gets to the
temperature that you desire. If you have a 125k btu unit, you will get there
faster than if you have a 35k unit. Undoubtedly you will need a differential
thermostat between the tank and the solar panel. A similar control could be
used to determine when the gas powered assistance is required and turn
on/off that unit.

I have a place in northern NH. 35k btu would hardly put a small dent in my
heating needs. I am not yet through insulating and it is 2200 sq ft. If 35k
btu is enough for your place, then a simple hot water tank would be easy to
acquire and adapt for your purposes. It picked up a used propane tank for
free from a place that was converting to oil. How big is your place?

In the case where you have solar heating panels on the roof, a tank in the
systems makes a whole lot more sense. You did not mention panels in your
original post. I had a friend who had a solar heated house. It had a
standard 40 gallon electric water heating tank that acted as a backup/assist
to the solar heated loop. They also had a huge (500 gallon) main storage
tank. That was several years ago, and I don't recall specifically how the
system was plumbed. It was a drain back system that did not use
anti-freeze.

For a very small cabin, a single hot water heater tank might be enough. I
have never constructed a solar heating system, but I do some reading on the
subject because I am interested in ways to heat my own place. For a seasonal
place, in a northern climate, anti-freeze is pretty much a requirement.
Drain back systems are subject to catastrophic failure from freezing.

Mythbusters had a show on last night where they tried to set a ship afire
using mirrors. Then were successful! That inspired me to begin thinking
about some type of a concentrating parabolic collector to grab a little heat
for my place. I am doubtful that I'll be able to do much more than
supplement a more traditional propane heating systems, and an existing coal
and wood stove. I'm no expert, but I might be inclined to tinker to collect
a few free btus.

Well Bughunter, I am in the woods of Maine, the house to be heated is well
insulated and I thought of this gas hot water heater is because of its low
output (35K BTU). I need less than that to heat the place.
I don't have to worry about building code.

 

[Bughunter]

Ideally, you want a less than 5 degree differential between your
delivery and your return, so the faster you pump it, the more likely
that is.

Why? I would think that a higher differential between supply and return
would indicate a more efficient operation of your radiators. Or, are you
talking about a different supply and return?

 

[Bughunter]

More heat lost to your rooms more quickly, yes, but the problem is the
first rad loses all the fluid heat to the room, and by the time the
fluid gets to the last rad on the string, it's "cold".
So what you'd get is the rad nearest the hot water tank is hot, but the
rest of them are quickly just cold. The idea is that they all need to
be hot. And to do that, you have to move the fluid faster than it can
shed the heat.

And it's code, actually, up here for hydronic systems (and oh what a
fun exam THAT one was...;-)

DJ

It makes sense to me now, since the goal is to get a nice even heat
distribution. I guess if all the heat does not get into the rooms on the
first pass, it gets there on later passes through the loop.

 

[[email protected]]

More heat lost to your rooms more quickly, yes, but the problem is the
first rad loses all the fluid heat to the room, and by the time the
fluid gets to the last rad on the string, it's "cold".

So use more radiators per square foot of floorspace towards the end
of the string, with less pump power and more boiler efficiency.

Nick

 

[daestrom]

That's an old hobby There's a tradeoff: either a) circulate lots of
higher temp water with lots of pump power, or b) circulate less water
with more radiators and let the water temp drop more, which reduces the
boiler inlet temp and makes it more efficient.

Or c) Pipe more radiators in parallel?? Seems like if you pipe a couple of
branches in parallel, then each branch has the same inlet temperature (don't
need more/larger radiators), and you can run the water slow enough to drop
the return temperature.

But slow moving water doesn't transfer heat through the radiator wall as
well as faster moving water.

Boiler efficiency only improves with cold return *if* the bulk water
temperature drops enough to affect the vent temperature. Most boiler
thermostats are set for a narrow temperature range and will cycle just as
much if you drop the return temperature twice as far with half the flow
(same heat demand). So other than saving pumping power (and needing more
radiators), what's the *real* issue?

daestrom

 

[Cosmopolite]

So a common feed header to the rads, and a common return header. Yep,
that's a common setup, too. The only downside is it takes about twice
as much labor and about twice as much piping. On a big loop, it might
be cheaper to put in a faster pump or a bigger boiler. But yep, an
option.




Especially when that water is almost half glycol. I'd bet that
increases the thickness of the stagnant adhesion layer. But to be
honest, just a guess. Chemical engineering is my wife's field, not mine
;-).

DJ

Add a surfactant.

 

[daestrom]

Add a surfactant.

Not the same thing. Surfactants will reduce the surface tension. Often
this is referred to the 'wettability' of the liquid. But the thickness of
the boundary layer against a pipe surface is determined by the viscosity of
the fluid, and surfactants do little to change this.

50/50 glycol is denser, carries less heat per kg, conducts less heat through
the boundary layer, has a thicker boundary layer, and takes more energy to
pump than plain water.

Bottom line, unless you really have to worry about freezing down to -40 or
something, use less glycol. With the OP's setup, unless the room is going
to lose heat and freeze, he would probably be better off with plain water
and a corrosion inhibitor instead of glycol.

daestrom

 

[daestrom]

Is the boiler a teakettle or a counterflow heat exchanger?

Doesn't really matter. If the vent temperature is the same, then boiler
efficiency is unchanged.

Remember, you're were suggesting using lower flow through the system to get
that lower return temperature. Even in a counter-flow heat exchanger, lower
flow along with lower temperature is not a 'slam dunk'. The lower flow
would also increase the boundary layer size and that would hurt efficiency,
not help it.

daestrom

 

[Gordon Richmond]

Well, if you live in an area that is subject to hard frosts, and there
is ANY possibility that an interruption in fuel supply or electricity
supply could cause your boiler to go down for a day or more, you had
better have anitifreeze in your hydronic heating system to avoid the
possibility of VERY expensive damage to your structure.

Can you imagine the cost of replacing frozen and split heating pipes
in a concrete floor?

I have floor heat in my garage, and baseboard heat in the house, and
both systems have antifreeze in them.

Gordon Richmond

 

[PCK]

More heat lost to your rooms more quickly, yes, but the problem is the
first rad loses all the fluid heat to the room, and by the time the
fluid gets to the last rad on the string, it's "cold".
So what you'd get is the rad nearest the hot water tank is hot, but the
rest of them are quickly just cold. The idea is that they all need to
be hot. And to do that, you have to move the fluid faster than it can
shed the heat.

And it's code, actually, up here for hydronic systems (and oh what a
fun exam THAT one was...;-)

DJ

would piping all rads to a 3 way valve for bypass help to balance such a
system

 

[daestrom]

Well, if you live in an area that is subject to hard frosts, and there
is ANY possibility that an interruption in fuel supply or electricity
supply could cause your boiler to go down for a day or more, you had
better have anitifreeze in your hydronic heating system to avoid the
possibility of VERY expensive damage to your structure.

Can you imagine the cost of replacing frozen and split heating pipes
in a concrete floor?

We get 'hard frosts' around here starting in October and ending in April.
Even when the house loses power for three days, it doesn't freeze. The
magic of insulation. Concrete floors, if insulated around the foundation,
will take a long time to freeze (several days). Not that you want to go
more than a day or two, but it isn't the 'lose power and the slab freezes in
one day' sort of scenario. If you have an idea how long it will be out,
you've got a couple of days to do something about it, not just one night.

More danger of the water piping to the second floor bathroom freezing than
the floor. Folks don't put anti-freeze in that piping ;-)

Interesting question, does PEX tubing fail when water in it freezes? I know
some plastics are 'freeze-proof' because the plastic has enough 'give' and
doesn't split wide open like copper or iron piping.

daestrom

 

[daestrom]

You could probably just put a conventional "screw stem" (as opposed to
ball) valve on the bypass. Varying resistance to the bypass would
divert flow to, or from, the rad.

Yep. Now that you say that, ISTR seeing just such a set up in an old HVAC
manual. One loop of piping all the way around the first floor and a second
around the second floor. Two 'T' fittings connected each rad/baseboard in
parallel with a portion of the loop, and a 'tuning' valve in the main loop
piping between the 'T's. Can't completely stop all flow from going through
the radiator with the valve full open, but can tune the system by starting
with all the valves full open and then gradually shutting the ones in the
room that is too hot, until the thermostat has warmed up the cold rooms.

daestrom

 

[Bughunter]

Interesting question, does PEX tubing fail when water in it freezes? I

know some plastics are 'freeze-proof' because the plastic has enough
'give' and doesn't split wide open like copper or iron piping.

daestrom

PEX is "freeze resistant", their term not mine. It will expand some and is
less likely to crack than copper, but the brand I used (Quest PEX) in my
house explicitly said not to let it freeze.

 

[Gordon Richmond]

Daestrom,

I might be away from home for 3 weeks at a stretch for work reasons.
Or a family could be away for winter vacation.

Being as you CAN use antifreeze in a hydronic heating plant, it seems
to me to be prudent; if freezing is indeed a risk. I know the plumbing
can freeze, too, and it's hard to anti-freeze protect that in a
regular home. But at least if the worst happens, you can get the heat
plant up and running again and work on the plumbing in relative
comfort. :>)

Gordon Richmond