Best to Run Hot or Cold Water Supply to Boiler?

viking_builder

Currently my home's steam boiler has cold water running to it. It's occurred to me that if I run a hot water line instead... I might get a couple of benefits because the water is pre-heated - like a reduction in the oxygen and some of the minerals being removed. Good idea or bad idea?

nicholas bonham-carter

hot water to boiler

not a good idea. many hot water heaters are fed with softened water which introduces salt into your boiler for an early demise.

if you work on many pipes, you may notice the hot side pipes are more clogged up with calcium than the cold side. if you don't want that calcium in your boiler, feed it from the cold, and pipe it well up into the wet return to reduce thermal shock. a well maintained system will need very little makeup water, unless something is leaking.--nbc

Boiler Talk

The old boiler

The old boiler in my home had a domestic hot water coil inside and so the water was cold into the coil and then heated water went into the bioler. 

Hap_Hazzard

I agree about the softened water

but if there's no softener, and no auto-feeder, I don't see a reason not to use the hot water. All that calcium and magnesium that gets deposited in the water heater precipitated out when the cold water was heated, so it's already been removed before it gets to the boiler. If you run cold water into the boiler, the minerals will be deposited there instead. Pre-heated water will also contain less oxygen.



You definitely don't want to run hot water through a water feeder. Dan has an article about a boiler flooding problem that was caused by that.

nicholas bonham-carter

Where's the calcium

In my experience, the calcium not only lines the hot water heater, but also coats the inside of copper, and steel feed lines on its way to the hot tap, and there is enough left over to line the drain pipes!

Maybe the pressure drop, when the hot side starts flowing, enables the oxygen, and calcium to precipitate out suddenly.

Once again, the amount of water needed for makeup on a stem boiler should be only gallons per year, unless there is a leak. Piping into the wet return is good insurance against any accidental thermal shock, and that point of entry may provide a safe, and easily replaced area for any calcium deposition which may occur.--NBC

Steamhead

If the boiler has an automatic feeder

check with the manufacturer. Some feeder manufacturers don't want hot water going thru their feeders, since the precipitates can get on the valve seat. This will make the feeder leak. 

Hap_Hazzard

It probably continues to precipitate

after it leaves the water heater, which is apparently what causes the problems with water feeders, but when you put it in your boiler and heat it up it's going to precipitate the minerals anyway, so you might as well use water that's already lost some minerals due to heating.



Think about it. Why would hot water have more minerals in it? The only reason you see them lining the pipes and water heater is that hot water can't carry them as well as cold water.

viking_builder

fyi

for this old boiler, I'm the automatic feeder

Henry

Softener

If you have salt in your softened water, you have a problem with your softener! Many Viking type boilers had a MM water feeder attached to the boiler. There is very little make-up on residential boilers as the only make-up is for blowdows and leaks. So, there were no problems with directly feeding a boiler.

jumper

agree with Henry

salt is better than calcium sulfate etcetra

elfie

lots of interesting discussing but ......

how much new water is reaching the steam boiler



ideally, virtually all of the new fresh water hitting boiler should be after doing blow downs which for a home boiler should result in much water being purged from system and not lead to much new water hitting system



maybe install a meter to better understand new water flow.



seems alot of effort here on what should be a minimal consequence issue.

Hap_Hazzard

Most water softeners use ion exchange

They exchange sodium ions for other cations, and since most of those cations carry twice the positive charge (e.g. Ca++, Mg++), they release about twice as many sodium ions. Only reverse-osmosis systems actually reduce the concentration of solutes, but whole-house RO systems are pretty rare, and I'd be reluctant to use RO-softened water in a boiler without a pH buffer.

viking_builder

not a lot

To your question, it's a very tight system so most of the water input happens when I flush out the mud each weekend. That said, it's a tight system because I baby it.... hence my question about the hot water... always thinking of ways to extend the life on my boiler.

elfie

water supply to replenish blow down

the water from most potable sources is fairly crappy and not healthy for a system



for a residential system, it would be interesting to know how much water is dumped each week (1-2-3 gals)  -  why not install a tank filled with pristine water (not sure where it would come from but lets say you found a better source than the stuff flowing thru the kitchen sink; maybe filtered tap water),



and use this water to replenish boiler



obviously it would not be an automatically replenished feedwater tank.



not sure the risk of thermal shock is a very big deal given the low volume of water entering your boiler (ie. maybe its a 20-35 gall capacity boiler)



i read so much on water softener use (some like it, some don't) and to me the water softener market relating to steam boilers has not been well developed - seems a water softener designed just for steam boilers may be of benefit.   there are so many mistreated steam boilers out there that may benefit from this - most boiler manufacturers are absolutely dumbfounded when you ask about using a water softener.

Hap_Hazzard

Recycle it.

I think you're on to something. Maybe that tank could be replenished with the blow-down water, after the gunk has settled to the bottom. I've noticed that it settles out after a few days, and if I pour the water off carefully, It looks pretty clean.It's probably devoid of calcium and saturated with iron. If you could keep the oxygen out of it it'd be perfect.

elfie

distilled water

isnt distilled water without oxygen; have to believe it can be bought somewhere or make it on the stove.  reusing blow down water seems abit of a challenge



even if you use water with oxygen in boiler, would it boil off fairly quickly with boiler in use?



i worked with a small commercial boiler that was leaking 8 gals per day via underground condensate return line that went undiscovered for yrs



and the makeup water source was directly from the potable water line (automatically fed) - this all may be giving you a heart attack



boiler is only 7 yrs old and leak is now fixed - hard to say how much damage was done.

Duff

Keep it simple

cold water would be my answer.The amount of energy you save after the water mixes and blends wouldn't be worth making a change.

All posts for this topic seem to be talking about introducing chemicals!

Refer back to the manufactures recomendations for your boiler. I'm sure there are pages of procedures on cleaning and maintaining your boiler all of which is good reading.

Good Luck



 

Henry

Corrosive

Pure water, either distilled or reverse osmosive is very corrosive! It is looking to attack any metal! IE, pure water is piped in teflon or silicone piping!

elfie

water without oxygen

so what does water become after all the boiling which removes lots of oxygen?



i do know that fish will dy if you boil off oxygen.



thanks

Boiler Talk

What is water?

Water or H2O or two Hydrogen atoms and an oxygen atom.  You can never remove all oxygen, but I hear you change newly added water by boiling it.  That's true to some degree.  You remove the dissolved air. 



http://www.physicsforums.com/archive/index.php/t-295974.html

Jean-David Beyer

Oxygen in water.

If you have a bottle of water, it contains oxygen in two forms.



According to its chemical formula, H2O, one oxygen atom is combined with two hydrogen atoms to make water. You cannot separate these by boiling. I am not sure that they will come apart even if you throw some on a red hot (dry-fired) boiler, but perhaps you can separate a few.



The water boiler operators worry about is of a different kind entirely. It is dissolved oxygen. Water is a great solvent for most everything. It even dissolves glass if you are willing to wait around, preferably a century or more. One thing it dissolves readily is air. Air is a mixture of about 4 parts of nitrogen and 1 part oxygen. The colder the water is, the more of a gas it will dissolve. Nitrogen does not harm most boilers because at low temperatures, it is not very active. But oxygen is. Heating it will drive it off, provided it has somewhere to go.