"How to" bleed air from furnace

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  #1  
Old 09-26-00, 06:24 PM
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Can someone provide me with step by step instructions on how to bleed the air going through the pipes when the furnace clicks on? It is a gas furnace with forced hot air coming through base boards.

This is what I know...

1. When furnace is cool, hook up hose to faucet and put where it can drain
2. Open valve
3. Turn faucet
4. Let water drain through hose until it is an even stream with no air spitting

Questions:

Is it "ok" if all the water drains out of the furnace? I know that I can replenish the water level using the lever above to put water into the furnace - level should be around 15, right?

How long will it take to get all of the air out of the system?

How often should I do this?

Thank you!!
 
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  #2  
Old 09-27-00, 03:44 AM
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Hi TPB:

It sounds like you are talking about a hot water BOILER and not a furnace. The hydronic experts are at www.heatinghelp.com Thanks. John.
 
  #3  
Old 09-27-00, 07:14 AM
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TPB:

Yes I can provide you with step by step instructions if you can provide me with some basic information about your furnace.

"It is a gas furnace with forced hot air coming through base boards."
No, if you have holes in the floor around the perimeter of your house with grilles over them where warm air blows out, that's a forced air heating system. If you have a "furnace" that heats water, then there will be radiators along many of the exterior walls of your house, usually under windows where the hot water flows through.
There are two kinds of radiator designs. The first kind uses cast iron baseboard radiators and if you reach under the baseboard radiator you will feel stiff hard cast iron fins on the back side of that radiator. With this kind of radiator, there will be a little screw or wheel at the top of EACH RADIATOR that you turn counterclockwise (when viewed from above) to let the air out of the heating system..
The second kind of radiator for a hot water heating system consists of a finned copper tube. It will have a sheet metal cover over it to hide and protect the fins, but you should be able to see the fins and feel them by reaching your fingers under the radiator. If these fins feel and look like a lot of thin sheet metal pieces on a copper tube, then look for an air bleeding screw under the end cover of the radiator wherever the copper pipe inside it turns downward to go into the floor. There will only be an air bleeding screw or wheel at the DOWNSTREAM end of EACH HORIZONTAL SECTION of this finned copper tube.
With both kinds of radiators, you open that screw just a little until you hear air hissing out or water dripping out. If you hear air hissing, then leave the screw open until the air stops and the water starts, and close the screw again. This is called "bleeding off the air". If you open the screw or wheel and nothing comes out, it's because the pressure of the water in the heating system is not high enough to reach up to that altitude. If that's the case, close the screw, add some water to the heating system and try again.

"This is what I know...
1. When furnace is cool, hook up hose to faucet and put where it can drain
2. Open valve
3. Turn faucet
4. Let water drain through hose until it is an even stream with no air spitting"

No, this sounds like the procedure for adding water to the heating system. You connect a garden type hose to a hose fitting on the furnace and the other end to a hose fitting on your houses cold water plumbing line and use the city water pressure to overcome the water pressure already in the furnace to force more water in. That reading of "15" is a pressure and means 15 pounds per square inch. The hydrostatic pressure of water is about 1/2 pound per square inch, so the pressure of 15 on the furnace would be enough to force the air out of radiators that are about 30 feet higher in elevation than where the pressure gauge is located.

"Is it "ok" if all the water drains out of the furnace? I know that I can replenish the water level using the lever above to put water into the furnace - level should be around 15, right?"

It's not a good idea to drain any water out of your heating system. The reason why is that the new water that you add will have dissolved oxygen in it, and this oxygen will react with the iron in your heating system to form rust. The water that's in your heating system now is already depleted of oxygen and won't cause the furnace to rust.

"How long will it take to get all of the air out of the system?" That depends on a lot of factors, but if the pressure is 15, and you don't have a lot of air in the radiators to begin with, it shouldn't take much more than a minute to bleed off each radiator. You see, you don't bleed the air out of the furnace, you bleed the air out of the radiators because in a hot water heating system, any air that gets into it will naturally float to the highest spot in the system, and these are usually the radiators on the top floor of your house because the furnace is usually in the basement. Also, you seldom ever need to bleed off the radiators anywhere except the top floor of the building because the air in the system will naturally float up into these radiators over the course of time anyhow.

"How often should I do this?"
You should do it at the beginning of each heating season, but you don't need to. It's only necessary to do it if your radiators aren't getting warm like they should. If they're not getting warm, it CAN be because they're full of air instead of hot water.

You really should add some oil to the oil cups on the water pump on your furnace. There should be three oil cups on that pump, one above each endbearing of the motor and one over the seal between the motor and the pump impeller. Different pumps take different amounts of oil, but for a typical pump you would put 1/8 fl oz in each motor endbearing cup and 1/4 fl oz in the cup for the seal between the motor and the impeller. These cups will have little spring loaded or threaded caps over them to prevent dirt and stuff from getting in where the oil goes.

Post again or e-mail me directly at [email protected] if you need any further explanation.


 
  #4  
Old 09-27-00, 07:18 AM
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TPB:

You should add oil to the circulating pump at the start of each heating season before you turn the pump on. Don't use just any oil. This is a special oil meant for this purpose that you should be able to buy from any place that sells plumbing and heating stuff. Phone up any plumbing and heating contractor and find out where he buys his.
 
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