Boiler water level

ansky

My boiler shows a normal operating range of what appears to be about 25% full up to 75% full for water level.  Are there any disadvantages to keeping the water level towards the lower end of the spectrum?  The reason I ask is because when there is more water in the boiler it takes longer to reheat and create steam, therefore using more energy and taking longer to heat the house.  Is there more to the story that I'm missing?

nicholas bonham-carter

water level

have a look in your owners manual [available on-line], and there will be a measurement for the water line from the floor. the modern designs of boiler section have very narrow passages whose water content is not great, so probably will not have much effect on the boiling times or fuel consumption.

i take it that the water line varies from 25% while firing to 75% while at rest, and that could be merely the effect of the pressure pushing the boiler water higher in the returns. the lower the pressure the better. do you know from a gauge yours is in ounces. more fuel is wasted by keeping the pressure higher than needed than boiling an extra bit of water.--nbc 

ansky

More info

The boiler is about 15-20 years old.  I'm gauging the water level based on what I see in the glass tube when the boiler is off.  Behind that glass tube is a chart showing normal operating range.  Basically from the bottom of the tube up to about 75% is considered "normal".  I have to add a significant amount of water to the boiler to get the tube from the low end to the high end of normal, which is why I'm saying it takes much longer for the water to boil and heat the house when the water level is at the high end. 

My pressure is fine.  The boiler shuts off at 10 ounces.

MrDvorak

Good question

I think that Ansky's question has a lot of merit because unlike turning a little more water to steam for a slightly larger pressure, heating extra water means 100% losses. Especially for us with oversized boilers, the savings of heating as little water as possible could be substantial IMHO. My water level shows higher level when firing because of the expansion of a large mass of hot water and a relatively small volume of steam in the system (that is my hypothesis anyway).

Rod

Boiler Water Level

As I see it  the burner puts out a fixed amount of heat. If you lower the volume of water while it will obviously make steam quicker, .you have also lowered the amount of transfer surface that the burner was designed to use, so your burner's efficiency has to be  dropping too so what the net savings of using a lower water level may not be as much as you initially would think. 

You have to keep in mind that a residential steam boiler has to be designed to operate over a wide range of conditions including severe cold weather. In severe cold if you have a lower than designed water level, your boiler will probably run out of water and hopefully the LWCO will kill the burner.

- Rod

Jamie Hall

Several miscellaneous observations...

Most boilers will operate quite happily within a relatively wide range, actually, on the glass -- typically one quarter to three quarters -- although there will almost always be a spot where they are happiest, and that is the level the manufacturer wants you to set the water line at.  But don't be a fanatic about it.



High water isn't good; you get a little more carryover water than you otherwise might (a lot more, if you let the level really go up) and things go boomp in the night.  Low water is just plain bad: a burnt out boiler if the LWCO is not working isn't a pretty sight.



But efficiency?  Ah yes.  Again, don't be a fanatic.  May I point out that it takes 1,000 times as much energy to boil a gallon of water as it does to heat it one degree?  So yes, if you are starting from a cold start, and you have say an extra gallon in there (more or less typical for an average modern residential boiler) you have to raise an extra gallon (out of what? 30?) that hundred degrees (a warm start will be much less, of course) -- but that additional heat is truly trivial, when compared with the heat you add to boil the water.