One of our readers is working on installing a domestic solar hot water heater in conjunction with a tankless.  They were going to go with a Rheem tankless to offset any additinonal temperature increase that was needed over the solar gains.  Unfortunately they found out that the particular unit that they were planning on using senses the incoming water temperature, buy ‘ignores’ water that is within 40F of the target temp (ie. the unit won’t cut on to work). This has caused them some problems because:

1) The max output on any residential line is 120F (49C) (this is canadian law it cant be any hotter than this in a residential home).
2) If the solar heated water comes in at 100F (37C) or warmer, the unit will not kick on. This means the output is 37C, a cold shower to be sure.
3) If you go to the commerical unit, the max temp is 180F. This much too hot for residential use (think of someone turning on the hot water at the sink to do dishes), but it would work from the 40F differential standpoint (ie. if the water is 60C or colder, then the unit will fire, anything warmer than 60C doesn’t matter as it would be warm enough for a shower).  Again this is illegal in Canada as the Max allowed Temperature is 120F.

The best solution is to more to a Rinnai Tankless water heater as this unit only requires there to be a 20 degree farenheight differentiation between water to be heated and heated water.  Therfor your shower will at the very least be 100 degrees farenheight which is plenty warm enough.

These co-heating water heating systems are quite complicated so its important that you talk to a prefessional regarding any plans that you have for your home or cottage.  Feel free to send us an email if you have any questions.