Navien Combi Boilers

[fixitflav]

Navien clearly state on their vids that a 200,000 BTU boiler can use 24 foot of 1/2" pipe.

That seems doable with the usual 20mbar supply. I make gas flow ~ 6m3/h, and using maybe slightly generous 14mm ID, in 24ft straight pipe I get pressure drop just over 7mb. In practice there's likely to be some fittings but it won't make a big difference.

The instructions for my old Ideal are worded a bit oddly IMO. Says minimum 20mbar MUST be available at the boiler inlet. It might be close, but it can't be quite 20mbar if it's 20 at the supply regulator. In any case, as it only needs 8.6mbar at the burner I'm sure it could stand quite a bit lower pressure at boiler inlet, the valve isn't going to give ~ 10mbar loss.
Says pipe minimum 15mm, but for a run above 3m 22mm must be used. But clearly that only applies up to a certain maximum length, which it doesn't specify.
Better if it just gave a realistic figure for minimum pressure at the boiler inlet, so pipework could be designed to suit.

 

[vulcancontinental]

Well I have no idea about Navien but if they're anything like Takagi or Noritz in the US they'll be pretty good. Time will tell but it looks an expensive heat exchanger that might actually deliver until perhaps it becomes a retrofit to a 30 year old OV system. The Koreans respond quickly to change and demand but like all start ups it'll be difficult in a saturated market. All depends on how much money they have and how clever they are at spending it.

 

[Deleted member 221031]

That seems doable with the usual 20mbar supply. I make gas flow ~ 6m3/h, and using maybe slightly generous 14mm ID, in 24ft straight pipe I get pressure drop just over 7mb. In practice there's likely to be some fittings but it won't make a big difference.

The instructions for my old Ideal are worded a bit oddly IMO. Says minimum 20mbar MUST be available at the boiler inlet. It might be close, but it can't be quite 20mbar if it's 20 at the supply regulator. In any case, as it only needs 8.6mbar at the burner I'm sure it could stand quite a bit lower pressure at boiler inlet, the valve isn't going to give ~ 10mbar loss.
Says pipe minimum 15mm, but for a run above 3m 22mm must be used. But clearly that only applies up to a certain maximum length, which it doesn't specify.
Better if it just gave a realistic figure for minimum pressure at the boiler inlet, so pipework could be designed to suit.

I seriously hope you never ever consider giving any advise on gas!

Saying a 57kw boiler is ok to work with less than 14mbr. And fittings don’t mater. FYI a 22mm elbow ads .5m to the length

Add to that the other 24 foot of pipe and some fittings you’d be lucky to get 12mbr

 

[fixitflav]

Make sure you clean the heat exchanger once a year.

I do it every 2 years, as per the manual. Seems to be enough.

In real use the efficiency was no better than a decent non-condensing boiler.

It may not meet the efficiency claimed (I have no way of knowing) but it plumes and produces condensate, so it has to be better than a non-condensing.

 

[fixitflav]

I seriously hope you never ever consider giving any advise on gas!

I don't, but why, what figures do you get? I could probably tell you a thing or two about pressure loss calculations. And what part of my post do you disagree with?

 

[Deleted member 221031]

I don't, but why, what figures do you get? I could probably tell you a thing or two about pressure loss calculations. And what part of my post do you disagree with?

Perhaps you can. But we all know it’s 1mbr loss max, meter to appliance.

 

[fixitflav]

But we all know it’s 1mbr loss max, meter to appliance.

Even for Navien?

 

[Deleted member 221031]

Even for Navien?

Why would Navien be different ?

 

[Deleted member 221031]

Naiven state in their MI’s 17-25mbr.

The other few mbr won’t make any difference!

 

[fixitflav]

Why would Navien be different ?

Why wouldn't Navien be different? Is 1mbar a rigid requirement, if so by whom (just asking)? From Navien's figures, they don't seem to think it is. Perhaps hard-work can add something.

 

[Deleted member 221031]

Why wouldn't Navien be different? Is 1mbar a rigid requirement, if so by whom (just asking)? From Navien's figures, they don't seem to think it is. Perhaps hard-work can add something.

When Navien quote a figure of 17mbr at the lowest. That’s a Working pressure, not the standing pressure you are quoting. Standing pressure means nothing.

Put a manometer on the input side of a boiler. Fire the boiler up and it will drop a few mbr.

 

[fixitflav]

Naiven state in their MI’s 17-25mbr.

Is that at the boiler inlet? Maybe Navien don't work on 20mbar supply pressure. If they assume 25mbar that gives 17mbar with my ~ 8mbar pressure loss. Be good to know before installing their kit in UK though!

 

[fixitflav]

Fire the boiler up and it will drop a few mbr.

I thought you said it was 1mbar max.

I'm still saying that the type of boiler most of this thread is about, with venturi etc, is different from older ones (like mine, for example) Do you agree now?

 

[Deleted member 221031]

I thought you said it was 1mbar max.

Meter to appliance 1mbr. Drop on working pressure.

 

[Deleted member 221031]

Is that at the boiler inlet? Maybe Navien don't work on 20mbar supply pressure. If they assume 25mbar that gives 17mbar with my ~ 8mbar pressure loss. Be good to know before installing their kit in UK though!

17mbr minimum 25mbr maximum. They aren’t saying 8mbr drop on the pipework is ok.