Thanks Disko.
I just was listening to Dr Karl podcast (20/4) via JJJ, and it was said that people will loose hearing after being exposed to 85 db (maximum safe) for more than 8 hrs. Furthermore, each increase in noise level by 3db reduces the "safe" time by half.

So 88 db 4hrs, 91db 2hrs, 94db 1 hr. 97 db 30 min, 100 db 15 min, 103 db 7 1/2 min, 106 db less than 4 min.

To give you an idea, a noise level in rock concert could be up to 120 - 130 db.

You can't really say 50 db without also including the distance measured from. Doesn't tell you much.

Hot water system would be positioned outside the house about 4 m away from master bedroom and 3 m away from family living room, but about 2 m away from a bedrrom of our eldest kid
(PS, it is a 2 storey house)
The main concern is the night time when there isn't too much ambient noise

<div class='quotetop'>QUOTE(Disko &#064; May 9 2006, 10&#58;07 AM) [snapback]170878[/snapback]</div>

Threshold of hearing 0 dB
Rustling leaves 20 dB
Quiet whisper (3 feet) 30 dB
Quiet home 40 dB
Quiet street 50 dB
Normal conversation 60 dB
Inside car 70 dB
Loud singing (3 feet) 75 dB
Automobile (25 feet) 80 dB
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one hand clapping... priceless.

sorry not exactly constructive, but i couldn&#39;t resist.

i&#39;m an idiot and will go to sleep now...

<div class='quotetop'>QUOTE(Joz &#064; May 9 2006, 10&#58;34 AM) [snapback]170889[/snapback]</div>

You can&#39;t really say 50 db without also including the distance measured from. Doesn&#39;t tell you much.
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Maybe this little snippet may shed some, further, light on the question. Many years ago I recieved a polite letter from the EPA demanding that I submit my car for noise emission testing (plus receipts for work done between the time I recieved the demand and the testing). They used a microphone on a tripod 1 metre from the exhaust offset 45 degrees for the measurement (with the engine running at 75% of maximum power revolutions; info taken from a large reference manual)

I&#39;d say with the window open if you have direct line of sight and you&#39;re like me and notice everything like that you might hear it.

But building a little brick enclosure for it would kill 50db easy. If practical off course, just run the thing for a night and see (if you&#39;ve bought it already).

Is this 52 dB SPL at 1 m?

If so, and given that it is outside, and a few metres from the house, I would say that it shouldn&#39;t be too bad, unless you live in a very quiet street. Having said that, it is possible that the level of noise generated during startup and shutdown could be substantially greater than during normal operation, and could be far more noticeable than a constant lower level hum during normal operation. If so it may be useful to ask about the duty cycle of the compressor.

Whether it is annoying is somewhat subjective but will also depend to some extent on the house, habits and the environs.
What is the house constructed of? (timber, brick etc.) Are the walls insulated? Is it older style with vents? What are the location and size of windows near the appliance? What type of glazing?
Does anyone sleep with the window open?
What is the usual noise level in the street and environs?

Also, remember that it isn&#39;t unusual for pumps and compressors to get noisier than spec after a few years operation.

Hope this helps.