New custom home build, need feedback

[Dana]

When I looked into the possibility of a tankless system and not getting outside air for the burner, the installation manual specifically gave a minimum sized room that is required to take inside air.

I totally agree that by trying to use indoor air to feed those two significant burners is not a good idea unless you have a whole house energy recovery system that is sized with this in mine. Throw in bathroom exhaust fans, range hoods, a gas stove or dryer, if present, etc., and you're throwing a huge amount of conditioned air out.

FWIW, it looks like the gas line feeding them may be undersized, but that's hard to discern for sure not knowing the distances and actual pressure or pipe sizes installed. The gas meter must be sized correctly as must the supply line to it.

It looks to me like 1-1/4" iron up to the tee to the right-most tankless, with a short run of 3/4" to the one on the left:

A pair of 199K burners can still be served with up to 40 "equivalent feet" of 1-1/4" plumbing (counting the equivalent lengths of every tee, ell and valve along the path in that 40' total):

 

[Jbrk]

I'm more impressed with the 1-1/2"? Water supply line coming in to the mechanical room.

My personal advice is to always upsize your gas main as high as possible. Ie when calling the gas service to run a new line, think of every possible gas appliance you could use in the future, and you'll get a nice 1-1/2" supply line and outlet off the meter.

 

[Sponsor]

 

[Jbrk]

Next question after reading the entire thread:

Why aren't there 40gal tanked units that have 199btu variable gas valves?

I like tankless the practical use of endless hot water.

I like tanked because it's more reliable.

What am I missing here?

 

[Dana]

Next question after reading the entire thread:

Why aren't there 40gal tanked units that have 199btu variable gas valves?

I like tankless the practical use of endless hot water.

I like tanked because it's more reliable.

What am I missing here?

What you're missing is the HTP Phoenix series (in particular the PH199-55, a 55 gallon water heater with a modulating 199K burner.)

A 199K burner on a tank is usually way overkill for most houses. A standard 2.5 gpm shower draws less than 90,000 BTU/hr, and 199K burner keeps up with a pair of those forever (or at least until the gas company turns off service because of the enormous bill being in arrears. )

Most homes do just fine with Phoenix Light Duty ( light duty only in comparison to the bigger burner commercial water heaters), with a modulating 76K burner. The PH76-50 is the 50 gallon version, more than enough for houses that don't have big spa tubs to fill, or super-deluxe his & hers dual showers with two gusher rain heads and multiple side sprays. It keeps up with a single 2 gpm low flow shower forever.

In the US the big orange box store carries the Westinghouse branded version of Light Duty. It's the same hardware, different label, different sales & warranty support. The Westinghouse tech support line rings at HTP's headquarters.