[Greenbuilding] Low flow with tankless heaters

[Niko Horster]

Hi Lawrence,

I have a Takagi TKD-2 for my domestic boost and have experienced some of the
same problems. I have a solar pre-heat tank (40 vacuum tubes into a 80 gal
storage tank then through a larger heating tank via 100 copper coil (the
larger tank is heated by wood/solar in winter) and then on to the Takagi to
do the rest if necessary. 
Initially I had set the temp on the Takagi to 115 or so (I don't remember
off hand the exact steps available on the remote temp controller), but
experienced some of your problems. I then fiddled with it for a while and
here is what works for me now. I have set the Takagi to 140F and adjust the
mixing valve to about 120 or so. This makes for pretty hot warm water, which
I can then temper down with some cold at the faucet. It does make the
fluctuating much better. I guess the idea is to establish a decent
temperature differential so that the Takagi has some "room" to regulate the
gas valve output. (and yes I know that this is hot water and can scald and
therefore might not work for everyone, depending on their sensitivity
towards high temperature water or liability exposure)

Hope this helps

Niko Horster