Backflow preventer / do I really need autofill?

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greenmountain

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1. In working on designing my small residential system (50k boiler/1500sq') and shopping around for parts, I've found backflow preventers ranging in price from $5 to around $1000... Anyone have recommendations for brand/model? Something reliable, long lasting, and potable water safe?

2. How necessary is it really to have an autofill/backflow preventer installed? I'm tempted to keep the boiler system separate from the rest of the supply plumbing. I realize this would require some frequency of checking the water level/pressure, but I've never had a boiler so don't really know how frequent this would need to be. Assuming no significant leaks in the system, once filled/purged/bled, how much water loss would be expected over time in a small system?
 

breplum

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Jurisdictional requirements prevail differently.
Some allow Watts 007 or 009 series.
They are vital in protecting public water supply. Others can pipe in on why water supply is just left 'on' normally.
If there is a low water cutoff on your system, then they can be turned 'off', perhaps...I'm an amateur on boilers.
 

fitter30

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The state, county, city or the water purveyor can dictate what type of backflow just depends on local laws. Since most residential boilers are not protected by a low water control. Leaving the supply on is the only protection against a low water condition and catastrophic failure (explosion)
Boiler system in theory once filled all the air removed never needs water added unless serviced or leaks. But with all the piping connections ,pump and relief valve you won't find a manufacturer piping diagram without regulator.
 
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John Gayewski

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This is not only a safety thing but also convenience. You will need to do maintenance and add water to the system from time to time. How else would you do it? You could add it with a pump, but then you have to drag things out and make a mess. Or you could just hook onto your water supply with a hose but then you have to be ultra careful not to overpressure your system which tops out at 30 psi before your relief starts spraying hot water everywhere.

It's a nice clean way to fill and maintenance the system. Not to mention the safety part.

The backflow preventer should have an atmospheric break in it so you know if its working.https://www.supplyhouse.com/Apollo-...ydHPlOyESWwpWyO10j38zBICwmjM54BsaAqVpEALw_wcB these are the ones we use most frequently. They should be installed high up.
 
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greenmountain

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private well, not connected to municipal system.
boiler has built-in LWCO but yeah, I don't want any explosions, though wouldn't there be noticeable signs of trouble before anything blew up? and isn't that the purpose of the pressure relief valve?
Was also thinking of some sort of redundant low water/low pressure shutoff routed through a control, but I haven't really researched how to do that yet. And/or ideally even some sort of wifi connected sensor that could send out an alarm if pressure in the system fell outside of parameters. Not this exactly but maybe something like it
https://www.amazon.com/Transducers-...ix=wifi+pressure+sensor,industrial,135&sr=1-3

For a leak/low water to result in explosion, pressure would drop first, then could rise catastrophically if enough steam was generated?

Was thinking to install a pressure reducing valve on the fill line up stream from a hose bib to avoid accidental over pressure, just without the always on/autofill. would have another hose bib close by on the domestic pluming supply side so filling would just be hooking up a hose.

I was thinking that with no autofill, there would be zero risk of contaminating potable water supply in case of a pressure reversal, and if there did happen to be a slow leak in the hydronic system, it would become apparent relatively quickly without the autofill rather than potentially going unnoticed for a while.
Sounds like the standard is to have an always on autofill though...
 

fitter30

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Boilers and water heaters blow up one way with limit and operating controls fail. Dry fire ( no water) their red hot. Fresh water comes into vessel flashes to steam, water to steam expanding 1700 times no relief valve could keep up.
 

John Gayewski

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private well, not connected to municipal system.
boiler has built-in LWCO but yeah, I don't want any explosions, though wouldn't there be noticeable signs of trouble before anything blew up? and isn't that the purpose of the pressure relief valve?
Was also thinking of some sort of redundant low water/low pressure shutoff routed through a control, but I haven't really researched how to do that yet. And/or ideally even some sort of wifi connected sensor that could send out an alarm if pressure in the system fell outside of parameters. Not this exactly but maybe something like it
https://www.amazon.com/Transducers-Direct-Pressure-Bluetooth-Transducer/dp/B07XBVHKG9/ref=sr_1_3?crid=29BDHFR98JE56&keywords=wifi+Pressure+Sensor&qid=1641079537&s=industrial&sprefix=wifi+pressure+sensor,industrial,135&sr=1-3

For a leak/low water to result in explosion, pressure would drop first, then could rise catastrophically if enough steam was generated?

Was thinking to install a pressure reducing valve on the fill line up stream from a hose bib to avoid accidental over pressure, just without the always on/autofill. would have another hose bib close by on the domestic pluming supply side so filling would just be hooking up a hose.

I was thinking that with no autofill, there would be zero risk of contaminating potable water supply in case of a pressure reversal, and if there did happen to be a slow leak in the hydronic system, it would become apparent relatively quickly without the autofill rather than potentially going unnoticed for a while.
Sounds like the standard is to have an always on autofill though...
The dual check with atmospheric vacuum break I linked is the best way to protect everything. No reason to do or worry about anything. If you think a leak is possible a sensor for that is your best option. The reason its standard equipment is because it's the best option, not because there's no possible failure.
 
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