Originally Posted by Admiral Nelson
I just installed an Isotemp SPA water heater 8 gallons and found that the water does not stay warm for more than 12 hours. Isotemp claim to be 24 hours which has been my experience so far. I was wondering what was everyone's experience with their tank. You have hot water for how long?
We recently completed the installation
of the IsoTemp 40 liter Spa water heater I mentioned earlier in this thread. My Admiral is very pleased with the results [It replaced a 6 gallon perfectly functional Raritan unit...]
[For those researching new water heaters: We paid US$520 - including USPS shipping
to Alaska- for the IsoTemp Spa water heater from Fisheries Supply. This seems to be much more in line with other water heater pricing than I see discussed in this thread...]
You didn't mention the specifics of how hot the water is [or isn't] before and after your 12 hour period of heat retention, nor your usage once the heating
source is off. You also didn't mention some of the other environmental factors that will influence your results.
For example, on our boat the engine heats the water to 180° - 190°F and I have the mixing valve [the one that comes installed on the IsoTemp] adjusted to 120°F [the temp of the water you get at the taps.] This mixing of 'superheated' water with cold to achieve the desired temperature at the tap yields 2 to maybe 3 times the tank volume of usable hot water (meaning pleasant showers...)
These are our results, which are likely lower than those of you with warmer 'cold' water per the following:
Note: The ambient water temp of our tanks- which lie against the hull- approach the ambient water temp we boat in- currently mid 40's F or cooler in winter and Mid 50's F in summer... If we're lucky... Mixing warmer cold water will yield even better results... [e.g., 70°F+ cold water would yield 3- possibly 4 times the mixed hot water volume vs. the 2-3 we currently enjoy...]
Regarding heat retention as relates to insulation
: Our water and space heaters are installed in the enclosed engine room (which averages 110°F ambient temp while motoring.) When we anchor
, we still have hot water 48 hours later if little has been used. If more is used (i.e., if more cold is mixed with the superheated tank of water- say a couple of showers) then of course it doesn't last as long- perhaps 24-36 hours- but we are still gathering data... We find it plenty for 4+ hot showers [2 adults; pausing water flow while bathing; still having to mix in some cold water to get desired temperature...] over a 3 day period, and dishes, etc.
To maximize our hot water retention at anchor
, when possible we shower
, etc, while motoring so the water heater has enough time to reach maximum temp before shutting down the engine.
One aspect of our install regarding longevity of hot water is our engine room also warms up to 80°F+ when we run the Espar heater, which is also installed there... The engine room rarely cools off below 60°F [even in 20° to 30°F ambient outdoor temperatures] and then only after days at anchor with no or little heat demand [e.g., sunny days in winter- below ~60°N- in our pilothouse reduce the run time for the Espar during those periods...]
This 'warm' engine room environment
reduces the burden on the IsoTemp insulation.
If yours is cooling
off prematurely without you using any or little hot water, try insulating the hot lines immediately adjacent to the heater, as some conductive heat loss occurs there... You could also further insulate the tank itself if it resides in a cool environment
You may also want to check the cold water line into the heater after an hour or so of no water being run. If it is warm or hot a small distance from the water heater, you may have a thermal siphon situation and need to install a check-valve or re-route the water line(s).
I also recommend you do some temperature measurements and track hot water usage after the heat source is off so you can estimate the heat loss factors.
An IR thermometer (or IR camera) will reveal any insulation deficiencies in the IsoTemp insulation layer.
I hope this is helpful.