On 6/23/2012 9:21 PM, Winston wrote:
snip


--Winston-- Now looking for an accurate NG totalizing flow meter.

I have one of those on the outside of the house where the gas comes in.
The test dial is pretty high resolution. I used that to determine
the gas input of my furnace.
Then I put a flapper on a microswitch that sits on a register.
I know how long the fan runs and how much gas is used for that time.
You have to factor out the preheat and cooldown time differences
between the fan and the burner.
I stuff that into a PalmIII and log/plot the on/off times for each
cycle and a running average.

http://myplace.frontier.com/~nm7u/pictures.html

That's an old archive picture.

Currently, it's been 1254 minutes since the AC last ran. Last few
cycles, it ran at about 5% duty factor.
I had it set up to track inside/outside temps too, but it took
a bunch of hardware in the middle and didn't really learn me much.

Works in winter for gas heat and summer for electric heat pump.

To do this with a gas water heater, you'd need to construct
some sort of flame sensor. You could tap off some signal inside
the heater, but I don't like messing with stuff that can blow
up the house if I screw it up. Insurance companies take a dim
view of that.