The 5K is total rebate. Heat pump is probably your best bang for the buck there. Actual measurable savings regardless of your current furnace situation (assuming you have a thermostat that deals with things appropriately). Can also do insulation (may be useful but if you blow in, you can not crawl through the attic any more or you will lose most of what you gained), solar (I could almost break even on a 5 kW solar install and then the power generated is "free") or a few other things.Apparently at triple glazed you're eligible for a 5k rebate from the feds.
So....spend 40k to save 5k ... or just spend 20k (or less) for double glazed.