reset w/o outdoor reset conntroller---will this work?

R. Kalia

I can't take credit for this idea, but I would like to bounce it off all the experts here before trying to implement it in our house. It is a very simple idea.

In most traditional installations, the thermostat relay starts/stops both the circulator and the boiler. In the system proposed here we require the circulator to run all the time---it is directly wired to AC power. The thermostat (a regular room thermostat from Honeywell or whatever) switches only the boiler.

So now you can set the aquastat to 180, but the constantly-circulating water will never get to 180, because the house will get too hot before that and the thermostat will shut the burner off. (Think about it---if 180 + constant circulation = too much heat, then since we already have constant circulation, the water temp won't reach 180, because the thermostat will shut the boiler off before that happens.) The room thermostat, not the aquastat, cycles the boiler. Obviously, you need a condensing boiler or in any case a boiler designed to handle low temp water.

So---and here's the kicker---the water temp will be exactly what it would be with outdoor reset and an ideal reset curve, because with the thermostat's assistance, it will reach and hold the exact temp needed to maintain the necessary room temp. Hence we have heat-load-responsive (rather than merely weather-responsive) lower water temperatures, with no outdoor reset controller, no setting or fine-tuning of reset curves. And you don't even need P/S piping because there is always full flow.

What is wrong with this? Because there must be something wrong, it is too simple, and if it were really OK you guys would all be using it and Tekmar would be out of business.