Hot vs. cold water feed for steam boiler?

davidsorkin

Hi,

  Can someone please explain why cold water should be used to feed the boiler? I have read this many times but have never seen an explanation.



When I bought my house in 2002 the boiler was fed with hot water. I am now doing some work and have the choice to leave it that way or switch it to cold. I think that one reason to use hot water is that it should already have some of the oxygen removed due to the fact that the solubility of gas in water decreases as temperature rises. Less oxygen --> less corrosion.



I cannot think of any benefit from using cold water or harm in using hot water.



Thanks,

nicholas bonham-carter

hot vs. cold water boiler feed

i have always wondered about that too. i do notice that the hot water lines seem to be more limed up than the cold, so i wonder if the anode in the heater causes some sort of change in the water.

as you should only be adding a small amount of water to make up for blow-downs, i doubt it matters which way the boiler is fed.--nbc

JohnNY

Hot water

Hot water contains larger particles of crud than cold water. That's right, I said "crud" and I'm a Master Plumber.

The manufacturer's don't care about your boiler. They care about fouling the seat of their crappy solenoid valves and having to deal with warranty requests.

Jason_13

hot water

The use of cold water has always been the norm. When you install a steam boiler for steaming crabs or browning bred etc where all the condensate is wasted I have always seen done with hot make-up water. As you stated oxygen comes out and dissolved solids drop into tank. Also keeping the steam as dry as possible.

Steamhead

Cold water, always

hot water can cause lime accumulations in the feeder valve mechanism, which will make the valve leak, flooding the boiler.



Check the instructions. All those I've seen specify cold water.

Jean-David Beyer

Curious...

I am not a professional, and I cannot disagree with Steamhead who most definitely is. But it seems to me that using hot water to replenish a steam boiler would actually be safer than cold, because the hot water heater would precipitate lots of the solids, the calcium deposits, and drive off  some of the oxygen in the heater tank (causing more rapid wear in the water heater), than if you put cold water into the boiler, where that would happen in the boiler if cold water were used. I would think that the boiler manufacturers would recommend cold water for fear that the hot water had gone through a water softener first, and this would be puttinig salts into the water and they would wish to prevent that.



Do you think that is the reason, or is something else going on?

Henry

Cold water

Having a cold water feed directly to the cast iron boiler is a recipe for thermal shock. Water make-up should always go to the condensate tank. In industrial aplications, we use steam injection into the condensate tank to maintain high temperature condensate and to create turbulance. This reduces the quatity of disolved gases and the amount of chemical treatment needed. I have seen some firetube boilers have cracked plates due to thermal shock when the maintenance staff did not repair the steam injector.

BTW, steam used in baking ovens is to make the crust. It needs to be a very wet steam.



Here is a boiler that had cold make up water directly to the boiler. Keep doing that type of installation. It just gives us more profitable work!

Jason_13

Hot make-up water

Many manufacturers today would like to see boiler feed tanks as opposed to condensate pumps today. the make-up water goes into the boiler feed tank. That means the make-up water will normally be hot as the boiler feed tanks during the heating season is normally pretty hot.

I guess the question may become at what temperature might hot water be bad or not bad?

nicholas bonham-carter

make up water feed location

or if you did not want the added complexity of an electrically pumped condensate feed tank, you could use a reservoir tank as the point of entry for the cold water.

i doubt that my battery backup for my boiler would run very long if i had a pump.--nbc