Tankless W.H.

Yves

Ok, here we go. Who makes the best tankless W.H. fueled by
LP gas. I'd like to run more than one app. and not run out
of hot water.

Mark Eatherton1

Contact

THE experts at Low Energy Systems at 303-781-9437. Talk to Jack Bellanti and let him give you his experienced opinion.

ME

Kal Row

forget best - first do the math....

btu required for - gpm of coldest steady water inlet - and rise to - highest steady required temp - you might need four of them in series/parallel pulling 185,000 btu each - if you have a house full of teens

1 btu per hour = 1 degree rise for 1 pound of water in one hour

8.33 pounds per gallon

remember you are actually dealing with gallons per MINUTE!!!

safest bet is to design for two serious showers or 4gpm each for 40 to 120 rise
if you live in a place where the street water is 40 or less in the winter – you will be hard pressed to come up with something cheaper than a pair of 40gallon rapid recovery old fashioned gas water heaters, set for 160 with a tempering valve on the combined outlet – you will seem to have an endless supply of 120 degree water – will cost you less to install/run/maintain than tHankless

now if you live in a warmer climate or can put a solar pre-heater behind it, then the economics turn toward the tankless biiiiig-time

on the other hand if everyone in your house takes baths instead of showers then it’s back to the tankless

“do the math, So you don’t take a bath!” – you have to know your load first

TEI

formula

Excellent advise on performing a sizing calculation first. Now here's the actual calculation:

Qin * efficiency = 495 * flow rate * (Tout - Tin)

Qin is the input of the unit in Btu/hr
Efficiency is the units efficiency in %
flow rate is the resulting flow rate in gallons per minute
Tout is the outlet (ie shower) water temperature in *F
Tin is the inlet (ground water) temperature in *F
495 is a conversion factor for *F, gpm, Btu, and gallons of water.

As mentioned, use Tin as the coldest groundwater temperature in your area (40 is a good, conservative estimate).

You can rearrange the formula to solve for flow, required Qin, etc.

Scott Denny

Flow rate

Qin(efficiency) = 495(flow rate)( ΔT °)
Great formula. But, how do you calculate flow rate demand?

Kal Row

multiply 4gpm times....

the number of girls over 12 years, times 80 degrees, times weight of water per gal, and you get the btu per minute required - that’s the only “politically incorrect” way of doing it - gives new meaning to the song "wish they all could be california girls..." - be a lot cheaper out there with all that sun to pre-heat with

Blackoakbob

Plenty of HW....

and high efficiency with a POLARIS water heater. I have a customer with a wife, 6 girls and 1 boy, 400 sq. ft. infloor and HW coil in an electric furnace ( heating system linked by a flate plate exchanger) and never runs out of hot water! They are good company to deal with, too.
The amount of space required is less than a couple of standard water heaters. I do recommend using a mixing valve for safety and the heating application.
Best Regards and Happy New Year to all.

Kal Row

you didnt say were - it makes a difference..

as the avg cold water temp is a big deal - 30 degrees big

dito on the mixing valve - it's a must not an option

Kal Row

Problem with something new (at least new here)is…

If people aren’t getting enough hot water with the old system, they blame the installer, but if you don’t get it with new technology, they blame the technology – so a lot of mis-sized/installed tankless is getting a bad rap

you need to do the math on the old system too!!!