You have a sophisticated system that's less than a year old and it's having a problem dealing with the first cold weather you've encountered.

You most certainly spent more than a few bucks on the equipment you describe, why aren't you calling your HVAC contractor ASAP?

Thx all; I did call my installer and they confirmed that the install specs for the hydronic airflow (we are hydro air) was too low; installer left 1st floor at default and it should have been at 1200cfm...they indicate that my knee jerk of 1600cfm is too high because air speed over coils won't optimize heat transfer...have lowered to 1200 and have a "hold at 69 degrees" in place to see how she does overnight, fingers crossed!

How's the system working? You should have your installer confirm that the hydronic coil is getting the proper water temperature also. It sounds like the install tech got through 80% of the install and called it a day without properly calibrating the hydronic backup.

mike_home: my heat pumps are 4 ton units each; I went with slightly oversized air handlers.

callights: Thanks for the tip on water temp, I will check on that, too. FYI, not sure if it's a clue but I am using the boiler for home hot water (showers) via indirect zone, and the boiler is maintaining I 150-170 degrees when the hydronic calls.

HVAC support were prompt and helpful via phone; I told them to hold off sending someone onsite until I've gathered more data (plus they were dealing with folks who had NO heat last weekend, much worse off than I).

With respect to gathering data, here's the latest: I've ended up setting the hydronic cfm to 1350; at that it looks like the system can maintain house at 68-70 if I wish...although wouldn't you know it the temp is now 50 degrees higher here in New England! Guess I need to wait for next cold snap for next test, but I suspect it's still not calibrated perfectly because it did seem to have trouble getting up over 70 degrees that cold day (after the cfm increase)...and no, I don't want my home at 72, it was just a test to see if hydronic could make that happen. Should I worry if it can only get up to 69/70 on a sub-zero-F day (as an indicator of some issue)? The VR1-40 is rated at 120-140K BTU, surely that's enough for a house my size?

Also, regarding mike_home your comment on the heat pump lockout -- the installer claimed that while manufacture says down to 0 F, in his experience the cost/efficiency wanes below 12 degrees...have you seen/heard otherwise and should I loosen that up a bit? Suppose I could "test" that, too, although I don't want to change too many variables at once.

The lockout should be set based on the efficiency curve of the system, the cost of electricity, and the cost of your backup fuel (taking into account efficiency). If you have cheap electricity and expensive oil, you may benefit from a lower lockout temperature.

Hmm ok guess I'll google around/check manufacturer site for hp and see if they publish such a curve. My VR1-40 rated at 87% I think for oil.

"Should I worry if it can only get up to 69/70 on a sub-zero-F day (as an indicator of some issue)?"

Maybe. A properly designed heating system should be able to keep the indoor temperature at 72 degrees while the outside is at the winter design temperature. Not sure where in New England you are located, but I would expect the boiler to keep you at 72 degrees when it is 0-5 degrees outside at night. If the VR1-140 is rated at 120K-140K BTU (not sure what is the efficiency), then you should be toasty warm under design conditions. I think you still have installation problems that need to be addressed. You already found one on your own, there a likely to be others.