Hiya,
UPS's aren't designed for what your looking to do. Mainly the 120v APC models, up to and including the data center class "Smart-UPS" for bottom of rack type installs are "stand-by" type intended to hold up data and computer systems for a short time until stationary power generators come on line and supply power to the site. (APC does make large multiple rack/row and entire data center class UPS's however the ones I have worked with are 208v single phase or 230v 3 phase input so that presents a challenge in a residential setting.)
Even with a gigantic UPS the issue you would have is that once a UPS is "on battery" it's converting battery to AC non-stop irregardless of attached load demand until the batteries reach a state of discharge configured in the UPS setup, normally 80% discharge, then it shuts off waiting for the utility or genset power to come back before it switches on line voltage to the connected devices. (this is to protect the batteries from complete discharge damage)
If your really concerned that your house will suffer damage from a power outage you should consult a local heating firm and ask them about an integrated low temp monitoring/heating/stand by generation system. However, keep in mind that the power reliability in NH has improved in the last 8-10 years, when we were first here, we used to loose power at least 3 or 4 times a winter, now unless there is a major storm, such as the ice storm of '08 when were were without utility power for 9 days, we don't loose power.
My 2 cents,
Tom
