Forced Air Hot Water Furnace Huge Banging Noise

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Old 03-17-11, 04:04 AM
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Forced Air Hot Water Furnace Huge Banging Noise

Hello,
New to the site done some reading the info here looks great!

My problem...I have an oil fired hot water tank that runs the heated water into the furnace (Air handler) and blows the air through the heating ducts in the house.
In the middle of the night the noise wakes me up it's so loud but i'm not sure if it's comming from the water tank or furnace, I can't get downstairs fast enough to tell. So here's what I've done, drained and cleaned the hot water tank, bled all of the lines to remove the air, ran the furnace on and off about 6 times and no noise,
thought I had the problem solved until I went to bed last night and it started again. Turned the furnace off and no noise the rest of the night. Turned it on this morning and the noise is back...

Any thoughts or suggestions would be great, I need to get this sorted out.

Thank you
 
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Old 03-17-11, 05:46 PM
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Just to ease any possible confusion, let's define a few terms first...

In general, when we hear 'furnace' we usually think of a heating appliance that heats air and distributes it to the home through ducts.

Your "(air handler)" term is what you should use for the unit that has the hot water piped to it, and the blower in it. That's not your 'furnace'.

When you say you have an "oil fired hot water tank" ... do you mean that you have an oil fired water heater that is used as a heating system? Tall, round, white?

I think that what you are hearing is expansion of the piping. The pipes are probably going through a too small drilled hole, or otherwise in contact with the wood framing somewhere. Copper piping expands quite a bit when it gets hot. If you 'set back' your heat at night, the piping cools and contracts. Then, in the middle of the night when the home cools, the whole system gets hot again, the pipe in contact with the wood starts to expand. At some point it expands enough to suddenly move and make a loud BLAM! ... it's actually sorta common... IF that's what it is. You do need to determine where the sound is coming from. Maybe you need to set up a cot and camp out by the heating system!
 
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Old 03-17-11, 06:35 PM
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Has the 'BLAM!' been an ongoing problem, or is it something only recently occurring?

If only recently occurring, have you changed anything within your home recently?
If ongoing, NJ Trooper probably got it right with the pipes sliding against the wood. You can follow the pipes around to see how they are secured to the floor joists. A tightly mounted pipe against the wood will definitely 'jump' when heating and cooling.
 
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Old 03-17-11, 07:19 PM
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Thanks Thomas, I had intended to ask that same question! It always helps to know the 'history' ...
 
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Old 03-18-11, 04:13 PM
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Thanks for the info guys, just to clear things up. I do have an air handler, not a furnace, and a tall, round white oil fired hot water heater that is used to run the hot water into the air handler.

The banging just started about 2 weeks ago, nothing has changed since the house was built Ten years ago, just this new banging noise.

I have looked and the pipes and they seem securely fastened to the floor joists, should they be a little bit away from the wood to provide room for expansion? Should I put a piece of rubber or something in between the joist and pipe to prevent the noise?

Originaly when the noise started I thought it was an air lock somewhere as I had just changed the main water filter 2 days before and had to drain the whole house to do it, is this still a possibilty?

Since draining and cleaning all of the "white stuff" out of the hot water heater and purging the air out again the noise has become much less frequent, maybe twice a night instead of 5 or 6 times.

Not sure what all of this means but I hope you can help me make sense of it all.

Thanks again for your help.

John
 
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Old 03-18-11, 04:48 PM
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How old is the HWH?

When there is alot of sediment in the heaters they tend to cavitate. It would be my guess you here the noise as,or after the burner heats the HW. I good way to find out is run some HW until the burner kicks on, then sit down and watch it....BOOM!!!!! LOL

You really need to change the factory drain valve to a full port 3/4" ball valve. This is the best way to get the sediment out. The factory openings are small and youll never get all the sediment out. Somtimes they start leaking shortly after you drain them, if you never done it before.

Mike NJ
 
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Old 03-18-11, 05:41 PM
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Hey Mike NJ,

The HWH is about 10 years old but only used part time for the first 5 years as this was my cottage and only here for weekends, then about 5 years ago moved in full time. The drain valve was changed to a full 3/4 inch type ball valve as you suggest at the time of installation.
I had heard that suggestion before and that's why it was done at that time by the HVAC installers.

Why does the sediment cause the heater to go Boom anyway??

Now...is it possible that I did not get everything out and that's why it's still making the noise, only much less often now because most of the sediment has been removed?

OR...Should the HWH be replaced?

I think we are getting closer to an answer...

Thanks to all for your help.

John
 
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Old 03-18-11, 07:07 PM
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I wouldn't replace anything. Something did change.
You said you changed a water filter, then the noise started. Then you drained and bled the system, and the noise was reduced.

You sure you got all the air out?
 
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Old 03-18-11, 07:47 PM
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Hi Thomas,

I thought I got all of the air out because I let it run from the bottom of the house to the top one tap at a time for about 30 minutes (closest to the HWH to the farthest away), but not positive. I could have missed something but don't think so. Will try cleaning the HWH and purging again in the morning to see if that helps but who knows. I would just like to get a good nights sleep without being woken up by this banging noise.

Thanks,
John
 
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Old 03-18-11, 07:48 PM
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OR...Should the HWH be replaced?
I dont replace mine until they leak. My heater is in a area that will not spill water all over the home. If yours is the same let it go.

As far as sediment goes, I put a pony pump on mine and drain it empty. You need to let air in somehow, relief valve, bleeder, or open a faucet. (hot side) Then when its empty I open the valve full force to stir up the bottom. Drain, open, drain, open...ect. Then I fill it up and do it again. It gets most of the crude out.

You can try this also.

If you have low water pressure or think there's a heavy buildup of sediment: consider the pressure flush.

The preconditions: cold water turned off, control set to pilot for gas, or power off for electrics, ball valve and curved dip tube installed. Now, open the valve and let the tank drain all the way down. This gives it a chance to fill with air. Close the ball valve. Open the cold-water valve until you can no longer hear water flowing.

Now what you have is a tank about two-thirds full of water, with that air compressed down to about one-third its original volume. When you open the ball valve to flush, it will flush at full force until the last of the compressed air is gone.

As far as the noise there are some things that could cause it.

If a rattle the heat trap nipple could be causing the noise. Replace the nipple with a regular nipple. (That is you have them)

Whats the pressure of your incoming water? Do you have an expansion tank?

Anode rods sometimes cause outgassing at faucets. this will give you air in the system and possibly banging.

If its not sediment, overheating causes banging. Whats the temp?

Mis-adjusted burners also, and has the baffle degraded? I have seen baffles fail apart and down onto the burner.

As far as cavitaion, when the water heats you will hear a boiling noise. The rumbling, popping, and banging noises you hear are pockets of water trapped between layers of sediment turning to steam as the water heats.

Thats all I could think of.

Mike NJ
 
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Old 03-18-11, 08:01 PM
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I don't think we are talking about the same thing here...or I am getting confused.

It sounds like maybe you replaced your whole house water filter. I have one in my house located on the cold water inlet to my house to remove junk coming from my well. After replacing, I will usually turn the tap on full blast to get any air out of the line.

It sounds like you just replaced this filter and now you are draining your domestic water lines, and not anything to do with a hot water closed loop boiler system.

Can you please check the gauge on your oil fired water heater and tell me the readings for temperature and pressure. By chance did you accidentally drain the boiler water?? If you could post a picture or two, that would also be helpful.
NJ Trooper can advise how to do post a pic for free.
 
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Old 03-18-11, 08:07 PM
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I don't think we are talking about the same thing here...or I am getting confused.

It sounds like maybe you replaced your whole house water filter. I have one in my house located on the cold water inlet to my house to remove junk coming from my well. After replacing, I will usually turn the tap on full blast to get any air out of the line.

It sounds like you just replaced this filter and now you are draining your domestic water lines, and not anything to do with a hot water closed loop boiler system.

Can you please check the gauge on your oil fired water heater and tell me the readings for temperature and pressure. By chance did you accidentally drain the boiler water?? If you could post a picture or two of your system, that would also be helpful.
NJ Trooper can advise how to do post a pic for free.
 
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Old 03-18-11, 08:20 PM
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Originally Posted by ThomasDB View Post
I don't think we are talking about the same thing here...or I am getting confused.
The OP is useing a domestic water heater to supply both domestic hot water and hot water to the hydronic air handler.
take a look at the first paragraph in post #5.
 
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Old 03-18-11, 09:14 PM
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Thanks for the clarification drooplug.
Understand the system now (I think). It is not a closed loop system.
Still, the noise started when the system was drained to replace the water filter.
Maybe some sediment got stuck somewhere it should not be since the system was drained, so a few fill/drain attemps may be good.
I would still like to know the temperature during a heating cycle.
If there is an expansion tank, is it saturated?
Any water on the floor?
On second thought, I better get out of this one before I suggest a wrong path.
 
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Old 03-19-11, 04:24 AM
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Ok, some answers to your questions...

Temp is set at 110, no expansion tank and no water on the floor.

As I said I will try to flush out any more sediment this morning and let you know how I make out.

Thanks again guys.
 
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Old 03-19-11, 07:56 AM
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Why does the sediment cause the heater to go Boom anyway??
I'm not sure if this got answered?

What happens is that the heat under the sediment layer causes localized 'hot spots' to develop and the 'mud' then percolates... just like those bubbles that come up when honey is cookin' up a big pot of tomato gravy... since the system is pressurized, it can cause the whole piping system to absorb the shock and transmit the noise to the structure... but it's really usually not as loud as what you seem to be describing.
 
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Old 03-19-11, 03:41 PM
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Ok, flushed out the HWH again, completely empty and ran fresh water through slowly and quickly, on and off for about 30 minutes. Purged all of the water lines in the house and now all seems to be ok. Ran the furnace on and off a few times, filled the bath tub twice and drained, no noise yet...

The only difference is the HWH doesn't make a gurggling sound when the oil burner shuts off, I guess because it's clean..?

All is good so far, crossed fingers...here's hoping. I'll update you again later.

Thanks again,
John
 
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Old 03-19-11, 04:34 PM
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The only difference is the HWH doesn't make a gurggling sound when the oil burner shuts off, I guess because it's clean..?
Yup. That's even more evidence that there was a lotta sediment built up in there.

Fingers crossed!
 
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Old 03-20-11, 10:27 AM
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Thanks to everyone, I slept great last night!!!!

No Noise, it must have been the sediment build up in the HWH.

You guys are amazing and I now love this site site more than ever, I will try and give back what I can to help others.

Thank you!!!
 
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