Trader4, I just figured out how to get fan only, and after 5 minutes, no noise. So I guess that clinches it, it's temp and not noise, and I can fix it by getting at least the last foot or so of the duct replaced or strengthened. My confusion on this temp vs pressure issue started because I have the setting at 71/69, and that seems too low to cause the duct to expand and make the REALLY POWERFUL BANG. But then, when I hold my hand to the vent, the air pressure seems pretty low too.
Thanks for everything. I really hope the home improvement guy gets this fixed. I'm going nuts from this noise.
The preferred way is to have a two stage thermostat that makes the selection. In some cases, it may be too difficult to do it that way because it takes one more wire from furnace to thermostat. If an extra wire isn't there and it's not easy to run, then you use the fallback mode of letting the furnace do it.
The advantage is the thermostat knows that if it's
60 and we're going to 70, then we want 2nd stage right away. Conversely, if it's been running for 11 minutes and it's only .5 deg to go, no sense in going to 2nd stage.
But the temp in that duct is swinging from 70 to 110 or so, which is plenty to cause enough expansion/contraction. If it runs through any colder areas, it could be even more swing.
But then,
It should be easy to fix once you have the wall opened up. It sucks though that you have to do that. Here's a thought. You might want to do the opening up part yourself. If you do it, you could open one or two smaller openings where you think the problem is. If you can see it, you might be able to figure out how to shove something in to support it, etc without tearing out a whole wall or ceiling worth of drywall.
It's the ceiling, not the wall, and I expect the home improvement guy will just tear out a small strip to reveal the duct. I imagine I just need a strip of about 1 foot by 3 feet. But we'll see. I'll do anything to get this fixed. I don't see that the whole ceiling needs to come down.
I don't know how you're paying the guy, for the job, by the hour, etc. But for something like this, if you can do the opening up, fiddling around yourself, you might save $$ and have a better result. Like I'm thinking the guy opens up one spot. Then you have to cycle the heat so you can see if it moves. Maybe you can't see it that well, did it really move or not, etc. Now you have to wait for it to cool, cycle it again. Then maybe open up another spot or bigger spot, etc. And if you think you have it fixed, I'd want to wait at least a day or two to make sure before closing it. If you open it and do the fiddling around, it might be better.
Hi, In the mean time try to run the air handler at lower speed if you can run the air handler at lpower speed and see what happens. Sounds like duct balance is off between exhaust and return side.
Hmmmm. Interesting. I have the fan at the lowest possible speed now. I'd didn't think about the balance, but then again, it's only happening at one duct.
Hi, Of course, heat can make the duct work somewhat expand and shrink every time heating cycle comes. When air flow is not balanced the pressure build up can make big banging sound when it is coming on or going off. Also it can happen with filter's resistance to air flow, etc. If you did not have the problem before new furnace.......
Hi, They have to measure air volume in CFM and blower speed setting, etc. For quick check, you can remove filter for one night to see what happens. better or worse.... My BIL is a commercial HVAC design engineer who helped our system when house was built with high efficiency furnace and high SEER a/c both two stage units. Runs very well on wireless thermostat w/o the bother of wiring.
In that case, there must be a separate thermostat for the fan control. I had an oil furnace, once, with a separate thermostat and it has a little knob in the middle that would turn on the fan.
Oil canning is most likely the cause, a very common problem with hot air heat. If the furnace guy put in the furnace and not the ducts, he is probably off the hook on this. Did the old furnace make the same noises?
The home improvement guy is not the guy to fix it unless he is familiar with this type of problem. You need a good sheetmetal man that knows how to design and install ducts.
Most likely, you have to cut the duct and install a flexible coupling to take up the expansion when the duct is heated. If you have long straight runs and do not allow for movement, you get oil canning. It should be allowed to float.
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The furnace guy should have been able to recommend a tin knocker, but it sounds like he just wants out. Now it is up to you to find someone. I'd ask around at the local plumbing supply house or a good heating contractor.
This is interesting. Thanks a lot Tony. I'm going to do some research on filters and get ones that allow the maximum air flow, and I'll report back In a day or two to tell you if it helps or not. I still don't see what I c an do if it is a balance problem. Is there a away of fixing that? Who do I call to look into it?
filters and get ones that allow the maximum air flow, and I'll report back In a day or two to tell you if it helps or not. I still don't see what I can do if it is a balance problem. Is there a away of fixing that? Who do I call to look into it?
Hi, You did not answer yet whether the problem came with the new furnace. If it started happening with new furnace maybe they sized it wrong or after install. they did not tweak the system well. I am a retired EE from Honeywell, not an expert on HVAC. Good luck.
Tony, it happened after the new furnace, but not immediately after. It mus t have been about 2 months later, which is why I do not hold the hvac compa ny responsible. I wish they would give me some curb side advice, but I thi nk they want out altogether. They don't return phone calls, and so on.
arch on filters and get ones that allow the maximum air flow, and I'll repo rt back In a day or two to tell you if it helps or not. I still don't se e what I can do if it is a balance problem. Is there a away of fixing th at? Who do I call to look into it?
The problem with the pressure theory is that Dom reported yesterday that the problem doesn't occur when he turns on just the fan. The fan setting on these systems is typically a higher speed than heating at first stage or second stage. It's almost certainly moving more air with fan only and would go through the same pressure range or higher. Dom can verify that by checking the airflow and sound from the blower. If it's making noises with first and second stage heat and not with "fan only", I don't see how it can be a pressure problem.
Dom didn't give a time from when the blower starts to ramp up until the noise occurs. If it's after the blower has already been at full speed for 10 secs or more, I think it would strongly suggest that it;s heat related.
Another simple test that could be performed would be to start up the AC and see what happens at the highest speed. It's too cold out, but it can still easily be done. Just open the circuit breaker for the outside AC unit. The furnace blower will still run, but the compressor won't start. See what that produces. That will have the blower at it's highest speed, max pressure.
One other question comes to mind though. Has anything else changed in the house? Basement been finished? Some registers closed? Did he check to make sure nothing has been placed in front of a register or return, blocking it? Room doors shut that were previously opened? Most or all of that shouldn't cause it to make noises if it was properly secured to begin with. But if a section of duct isn't installed correctly, those things could be what creates the conditions to make the noise happen, at least if pressure is a factor.
And in the end, it most likely doesn't matter, because the ducts are supposed to be installed so that they don't move. Fixing that is probably the only thing that is going to produce a solution.
search on filters and get ones that allow the maximum air flow, and I'll re port back In a day or two to tell you if it helps or not. I still don't see what I can do if it is a balance problem. Is there a away of fixing that? Who do I call to look into it?
And I think that nails it. Terrific. My next step is to remove the sheet rock under the duct that causes the damn shot-gun level clanging, do whatever I need to do to stop it (possibly getting a duct pro to replace it), then fix the sheet rock. Thanks. I feel confident going into this.
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