We just installed a Lennox XP21 heat pump / AC unit and a Lennox SLP98UHV furnace. This is our first heat pump. The heat pump was set to operate until the outside temperature hits 30 degrees. In our spring in Minnesota this year the heat pump has been operating to provide heat nearly 100% of the time to the exclusion of the furnace. However, inside the house, when the heat pump is operating at temperatures lower than about 45 degrees, we experience a noise that is somewhat like riding in a car with only the back windows down. The noise is not loud, but in a very irritating sound frequency range. I think that the source is either the compressor noise coming through the tubes or some virbration caused by the main plastic blade fan on the outside unit. The unit is positioned quite close to the house and I am thinking that either the compressor or the fan could be the noise source. We had an AC unit mounted in the same location previously and did not experience the same noise. However, the old furnace fan's high speed may have masked it. What ideas do you have for isolating and overcoming this noise issue?
Type of HVAC: Heater & Furnace
Nothing yet - still trying to isolate the issue
Hello I'm Norman & thanks for using JustAnswer. Please do not press accept or leave feedback until you feel we have reached a resolution.
How are you today?
I am fine.
Good. This noise that you are hearing is it happening about every 30-90 minutes?
We havent timed it. Are you thinking defrost?
That's exactly what Im thinking. Those who are not use to a heat pump may be surprised by the level of noise when the unit goes into defrost. The best way to know is to run to the unit when you hear it and see if the oudoor fan has stopped and the unit starts steaming.
Some other pointers would be to inspect the length of line-set and make sure the straps are not too tight, make sure the lines are not touching wood or any part of the structure at any point. Also make sure your filters are clean. Air restrictions cause units to get loud as well.
I'm not sure that it has been that cold yet. Please explain what you mean by "run the unit". In trying to investigate the noise I have gone outside when the noise is heard in the house and the unit is running and there is no steam.
Ok first question, is the noise intermittent or steady?
When we hear the noise it is steady. We seem to have the noise at the lower temperature ranges.
In other words we do not have the noise at all times when the pump is running.
The compressor is working harder at lower temperatures. I am still concerned that you are hearing the defrost mode. When operating the unit in heat mode, next time you hear it happening, go to the outdoor unit and see if the fan is turning, if it has stopped it is in defrost and that is what you are hearing.
My personal heat pump is very noisy in heat mode, especially when in defrost. My wife complains all the time.
You may have a point with respect to the lines not being isolated. However, the defrost is the easiest to test. Our current exterior temperature is 46 degrees. If we crank up the thermostat can we force the unit into defrost to test or must we wait for colder exterior temperatures?
You need to wait for it to go into defrost. A technician could force the unit into defrost using a jumper at the outdoor unit.
Inspect the refrigerant line-sets and also the indoor unit. Make sure it has good vibration isolation. The indoor unit should have virbration isolation pads under the unit and not be touching the structure at all.
Ok - now that we have something to go on, my wife (who is bothered the most by the noise) just turned up the heat. The pump went on and we get the vibration and noise inside the house. The compressor tubing appears to be the source of the vibration. That is, when I grip the bare copper tubing and the foam tubing together, I get less noise and less vibration. This might be an indication that the bare copper tubing is at least vibrating against the foam insulated tubing along the run inside the house.
I think its probably touching the framing members or the wall as it passes into the house and along its route.
Is it covered by sheetrock?
The tubing is not covered by sheetrock. The furnace is in the basement. The heat pump is at ground level (above). The tubing looks like it exits through the first joist that sits atop a concrete block wall. The tubing would be running through that joist, then exterior foam insulation and then finish stucco.
So areas of vibration are limited. Check them all and if you need to stuff something soft in there around the framing member. Anything to keep it away from the structure.
Ok. We can make sure that the tubing doesn't touch the framing. Regarding the bare copper tubing and the foam insulated tubing that rattle together - should these be bound more tightly together or should they actually be isolated from one another as much as possible?
I Insulated the large pipe and lay the small pipe next to the insualted large pipe. I then duct tape them both together about every 3 feet or so.
As installed the two tubes are taped together with electrical tape.
The tubes are installed as you would install them but vibrate agains each other.
They shouldn't is the insulation rigid or soft?
It shouldn't vibrate but I believe you.
Play around with the piping and see what you can do to dampen it. Try multiple things just don't pull on it or bend it as it may damage the piping.
Ok. Is there any possible chance that the plastic fan blade on the unit itself is creating a vibation that is coming all the way through the unit. The compressor ( would think) should be pretty well balamced out so that it would not create a vibration. The heat pump nuit itselff stands on the plastic feet and base recommended by Lennox. I'm wondering if the fan blade itself is creating a vibration. When I listen to the fan blade noise it sounds like there is some flex in the blade (or the blade is not balanced) that I dont recall hearing with the metal blade (on the old AC unit. Is this a crazy thought?
It's possible. Push down on the cage around the fan and see if that quiets it down some.
No difference. The cage / grill is tight. The fan blade itself makes the sound like I used to get when I would clothespin playing cards against the spokes of my bike when I was a kid - only quieter. Its as if the fan blades are "slapping" the air versus cutting the air like a metal blade would.
How old is the unit?
brand new XP21
Within a year old?
two weeks old
okay that unit should not be very loud. The higher efficiency units should be very quiet. At this point you have found what we think is the source of the noise. call the installing contractor back and have him check out that fan. You have parts and labor coverage on a new system for probably at least 1 year. They should gladly return and fix it.
Ok. I will have the contractor check out the lines and the fan. However, just to reinforce my understanding, it is your view that an issue with the fan or fan blade could be the source of the vibration that is coming into the house through the tubing and creating the noise. Please confirm. Finally, before I accept, is there a way to print our conversation?
The fan is not likely transfering noise through the unit. You would be hearing the fan through the walls of the home. The refrigerant piping noise is likely to be in addition to this.
If you want to print the conversation. I suggest using word, copy and paste the info into a new word document.
does that do it for today?
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Yes- Thanks for the help!
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