Posted by bob haller on October 24, 2011, 3:25 pm
> Tankless water heaters do have some quirks that are easily worked with or
> worked around. The only real problem I have experienced or know of from
> people that don't talk nonsense is the minimum BTU output capabilities of
> the gas burners attemting to use very low water trickles from the faucettes
> or into home hydronic systems at the low usage end.
> Most of the gas units are 180,000/h - 235,000 BTU/h There are no two water
> heaters in series needed.
> It's pretty easy to calculate in Imperial measure.
> 1 BTU to raise 1 pound of water 1 degree F.
> 185,000BTU/h heating water 64 deg. F (30F input to 104F shower) = 2890 gal
> per hour
> or 2890 / 60 = 48 gpm.
> You should be able to take about 48/3.0 gpm = 16 showers, at one time.
> Now those are Input ratings on the BTU and the actual efficiency is about
> 83% on the (noncondensing) cheaper units.
> Your gallon may vary depending on geographic location and your ice may not
> go through the heater when frozen (ooops)
> ----------------"bob haller" wrote in message
> OP may need 2 heaters in series to getn the cold winter water hot
> enough for a good shower.
> theres lots of tankless discussions here mostly talking about their
> problems
manufactuers sometimes recommend 2 tankless in series in cold
climates, and some of the issues have no easy work arounds.
take power line units which use the power line for powered venting.
a power failure in this type mean zero hot water during any power
failure.
and running new gas lines all the way back to the meter or even
possibly a complete new serice can cost thousands.....
Posted by Mho on October 24, 2011, 11:39 pm
Manufacturers never recommend two units in series but rather in parallel.
The minimum BTU requirements must be met or the burner will not ignite. Min
was 15,000 BTU and the new one is lower. People all look at the top end with
the scare tactics you are putting out. Top end is not a problem and lots of
reserve capacity is had with anything over 120,000BTU/h . Two showers and
the dishwasher, simultaneously never bothers mine but rather the well pump
capacity.
3/4" gas line is all that is required. Just another tap off from the
manifold.
I have my heater backed up from my solar system electrical. My power has
never failed more than a few hours in severe storms.
----------------"bob haller" wrote in message
manufactuers sometimes recommend 2 tankless in series in cold
climates, and some of the issues have no easy work arounds.
take power line units which use the power line for powered venting.
a power failure in this type mean zero hot water during any power
failure.
and running new gas lines all the way back to the meter or even
possibly a complete new serice can cost thousands.....
Posted by bob haller on October 24, 2011, 3:29 pm
> It's pretty easy to calculate in Imperial measure.
> 1 BTU to raise 1 pound of water 1 degree F.
> 185,000BTU/h heating water 64 deg. F (30F input to 104F shower) = 2890 gal
> per hour
> or 2890 / 60 = 48 gpm.
> You should be able to take about 48/3.0 gpm = 16 showers, at one time.
most home water tank type heaters are set at 140 degrees to support
dishwasher operations.
so your 104F output water will get you a cool shower with dirty
dishes.....
your far better off with a vectra high efficeny condensing heater. it
combines the best of both worlds but is costly
Posted by Mho on October 24, 2011, 11:33 pm
I would challenge you to take a shower much more than 104 F. A hot tub with
105 will prevent you from getting in. SHowers can stand a bit higher due to
lots of air mixed on your body. 96 F is a cool shower.
I run mine about 140 F as that is the recommended temperature by Legionella
experts, not as the tankless manufacturers recommend. It also gives me
faster morning recovery from house temp setback during sleeping periods,
than a lower temp. Setting a personalized temp at each faucette before usage
is a dumb thing to do and will be forgotten when doing dishes or other temp
critical job. Setting a tankless to higher temps. increases the need for
maintenance due to hard water deposits in the unit.
These things have plenty of BTU/h capacity and that point is moot.
Ultra high efficiency is not needed for occasional usage at a cottage is the
OP asked about and would never pay for itself.
--------
"bob haller" wrote in message
most home water tank type heaters are set at 140 degrees to support
dishwasher operations.
so your 104F output water will get you a cool shower with dirty
dishes.....
your far better off with a vectra high efficeny condensing heater. it
combines the best of both worlds but is costly
> It's pretty easy to calculate in Imperial measure.
> 1 BTU to raise 1 pound of water 1 degree F.
> 185,000BTU/h heating water 64 deg. F (30F input to 104F shower) = 2890
> gal
> per hour
> or 2890 / 60 = 48 gpm.
> You should be able to take about 48/3.0 gpm = 16 showers, at one time.
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> worked around. The only real problem I have experienced or know of from
> people that don't talk nonsense is the minimum BTU output capabilities of
> the gas burners attemting to use very low water trickles from the faucettes
> or into home hydronic systems at the low usage end.
> Most of the gas units are 180,000/h - 235,000 BTU/h There are no two water
> heaters in series needed.
> It's pretty easy to calculate in Imperial measure.
> 1 BTU to raise 1 pound of water 1 degree F.
> 185,000BTU/h heating water 64 deg. F (30F input to 104F shower) = 2890 gal
> per hour
> or 2890 / 60 = 48 gpm.
> You should be able to take about 48/3.0 gpm = 16 showers, at one time.
> Now those are Input ratings on the BTU and the actual efficiency is about
> 83% on the (noncondensing) cheaper units.
> Your gallon may vary depending on geographic location and your ice may not
> go through the heater when frozen (ooops)
> ----------------"bob haller" wrote in message
> OP may need 2 heaters in series to getn the cold winter water hot
> enough for a good shower.
> theres lots of tankless discussions here mostly talking about their
> problems