Wet/Dry based boilers?

scott75

Hi guys, very elementary question here. I'm new to HVAC and don't do much with hydronics. Only recently have I heard wet based and dry based boilers. What is the difference? Does the wet base have water sections surrounding combustion chamber? Someone just posted a thread on HVAC-talk similar to this and said that the refractory material isn't NEEDED (but obviously it is very good practice to have one) on a wet based boiler. Is this true? What are other differences between wet and dry? Pro's and con's?

Scott

DaveGateway

You're partly right

A wet based boiler has the boiler water surround the burner flame. Of course it doesn't always have sectons like a steel boiler (Laars Max, Energy Kinetics, Burnham LE, etc)
And a refractory is usually not needed or wanted since the cast iron/steel is absorbing the heat directly and being kept from burning by the cooling effect of the boiler water. A dry base boiler has a fire box under the boiler and will need refractory material oposite the burner (target wall) to absorb and help distribute the heat back up into the bottom of the boiler. Since the fire is under the boiler, most dry based boilers are vertical tube to get the exhaust gases past the boiler and out the top mounted flue. This adds to the stand by loss, puts all the heating stress on the bottom of the boiler vessel and of course refractory material breaks down over time.

scott75

Does the boiler water actually surround both sides, back, bottom, and (of course) top? On a dry based boiler, is there nothing between the target wall and boiler jactet?

Unknown

You're correct

Both times.

Noel

J.C.A._3

Depending on the age,

A dry base could have alot of different materials under and beside the fire. Rockwool,vermiculite and asbestos were used . The rockwool and asbestos fireboxes were usually lined with a refractory material like a wetpack or a water mixed (usually asbestos based)mixture. I can't remember the trade name of the stuff as I haven't used it in 15+ years.

There are also quite a few "wet leg" boilers still out there. The water didn't surround the fire like a wet base , but the sides were heated by the flame. Most have a return pipe located near the bottom of the jacket, one side or the other but the good ones had drains on both legs, so you could drain off the MUD on a service. The fire wasn't surrounded by water(a true wetbase design) but tried to transfer it to 3 out of 4 sides.

If you have to remove one of the wet leg boilers, I highly suggest getting a sample of the firebox. If there is any asbestos in the mix, get a professional to remove it before proceding. Some wetlegs were converted to oil or gas and the facing around the burner insertion point was sealed with suspect materials. If you can see it there, assume that the backing is the same.

Hey Joebrix,as far as not having a lining in the firebox/chamber I will respectfully have to say that it depends on a few different circumstances. Sometime when your having a problem with a high CO reading, give it a shot. The numbers become extremely surprizing. I don't recommend this for all wet base units by any means, but on a few true problem cases, I've found it to be a step in the right direction. Once the refractory heats up, the heat tranfer is almost the same as one NOT being there, but the quality of the fire increases a bit. Chris

DaveGateway

You're right Chris

I was just making a generalization on most units. A few burners like Carlin might require a refractory pad be used in the base of some models due to the flame pattern.

fares

TSSA gas technition G#

hello guys,

very soon i will do my G3 TSSA exam, i am wondering if there is any one of you went through would help me or advice me what to study more (the code books + modules)

thank you!

Jason_13

Even another

Don't forget there are also wet leg boilers, water on both sides and back but not beneath the flame.

Than we have water tube boilers.

sdevito

what manufactures make wet base triple pass residential gas boilers? Is Budures on of them?