is it wise to hook a solar water storage tank to an on-demand water propane heater to provide preheated water so they dont turn on or work less? i have been told that once an on-demand heater wants to come on with the minimum flow rate the heat sensor will cycle on and off, wearing it out with already 140 degree water… is there a fix if this is true? what if i cheated the heater to have 80 degree water instead of 140-160 available? it would have to heat less, but like itd have a regular work load..
2 plumbers have 2 different answers. i just think their experience doesnt know and mainly my question isnt answered very solid.
i think i get it now…
if flow rate is higher, the burner adjusts to use more gas to heat faster.
and the dang burner just comes on regardless of water temp because its a flow rate switch…
and a set point is how the heater knows how much to heat the water within its flow rate so it can actually save some gas there like RancidCrab’s boiler circulation setup.
so if i feed a on-demand 140F h20, its going to be heated even more. yikes!
but what if i make the set point high?
id have to so the flame would be minimum…
still, its a cost.
this was great help you guys. i think i will keep them separated and find a mixing valve to sense the gravity hot tank going cold so it can switch the water to the rinnai…i have been at looking those mostly.
i used to have a french brand (forgot name) many years ago, and i just always ran it full on, no cold mix at all..it was either on, or it was off..went to solar then. i need just alittle more hot water in the winter to wash everything. ty again!
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{ 3 comments… read them below or add one }
Actually, the instant water heaters that I’ve encountered come on and heat as soon as and as long as there’s flow going through them. When the flow stops they stop. Doesn’t make any difference what temp the water going through is, it’s whatever the unit is supposed to put out at the exit end.
2 Plumbers and 2 opinions? I’m going to split the difference… it depends on the appliance.
On-demand heaters operate on flow and most fire full out when called. They just don’t adjust the flame based on the waters supply temperature. This is why many people will complain about temperature fluctuations from their on-demand water heaters.
A few, Rinnai specifically, don’t operate ‘blindly’. It adjusts its flame to raise the water’s temperature to the set point. It constantly adjusts this flame, along with a flow valve, to keep the output temp constant (well pretty constant anyway).
While a solar panel preheat won’t make a bit of difference with some appliances, it will with an appliance like that offered by Rinnai.
Yes, I can back this up. I’ve used the Rinnai on demand water heater as a boiler. It kicks butt in this application. Variable burner providing 15,000 to 180,000 BTUs input. Instant hot water output. Reliable… Rinnai frankly has no competition for reliability in the N. American market.
When I operated my baseboard systems, I could hear the Rinnai adjusting rapidly to the temperature of the return water. Starting cold it would burn full out, but the moment warm returned, it dropped its burner rate. Basically using only the required amount of fuel to meet the set point.
Alternately, I’ve seen a Takagi installed as a boiler. The homeowner complained about going through a tank of propane a month. The Takagi clearly didn’t adjust its flame and burned full out whether one zone was calling, or all five.
So…
I don’t think it would make a bit of difference in fuel usage if you put a solar panel before a Bosch or Takagi. However, it would reap direct savings before a Rinnai or appliance with similar operating characteristics.
Regards!
Research I did on tankless water heater base there output on raising the temperature as set # of degrees. If you read the fine print, the stated output is with a set inlet temp. Deep wells, different water distribution systems, different seasons all affect inlet temp and cause some northern plumbers to stay away from tankless. Rannai systems shows commercial installations with multiple heaters connected in series. The faster the flow the less time to heat the water and the need for multiple heaters. I don’t think you would have any problem with preheated water.