Hi Lynn, you didn't say where "out here" is. Where you are located makes a big difference in which tankless heater is, or will be, ok for you (ground water temp, and all that stuff). Also, your hot water usage plays a big part in what size (btu's) heater you will need.
Even though my company sells the AQ-125, it is usually a marginal choice for a whole-house application. The T-K1 (165,000btu's) or T-K2 (185K) or T-M1 (235K) are much better suited to supply a whole home, or to be used in cold climates.
If your e-mail addy is anything to go by (southslope.net) ALASKA? Then your pro' is right, the AQ-125 is way too small (underpowered).
If you would like more info on the physically smaller, but more powerful T-K & T-M models, please e-mail me and I'll be glad to help. My # is (337) 598 2600 (Louisiana).
Happy New Year to all you folk. Sorry I haven't been around for a while, I almost broke my back a few weeks ago and sitting at this desk kills me.
How is Henry in MI? I haven't seen him in a while? I hope he's OK.