This is a passion of mine. I just looked at the smart meter history for our home of 13 months to see the difference vs. our first full month in the house... For a nearly identical "average" temperature of February (2 degrees warmer average), we over 20% more efficient or about $25 less out of pocket in a peak winter month... Summer air conditioning savings will be roughly double this. The key changes...
Everything practical changed to LED bulbs. The most amazing difference in wattage was under cabinet lights in the kitchen (20Watts each times 12 bulbs, which came out to ~50 per year difference based on KwH rates really???). The next biggest were the use of dimmers (dimmers actually increase up to DOUBLE the energy usage via use of resistance to dim the light). A fully bright light is actually far more efficient than a dimmer! I now have my eyes on a new 1/2 inch deep LED ceiling lamp replacement that lasts 15+ years and would allow us to cover the hole the can light hole creates in the upper ceiling envelope AND use LED entirely in those to reduce from 60W bulbs to ~6W. Pricey though and we don't use the cans enough to justify on energy usage alone.
Dropped the electric hot water heater temperature (we have gas heat, but electric water due to the reno of our home a few years ago). And did the maintenance to remove sediment from your heater just using a hose to drain out sediments at least twice per year. It reduces the crud on the bottom, the stuff floating around on the burners, then everything just works better & of course lasts longer.
We did insulate the crawl spaces with at least 1" hard foam board, high grade duct tape I already had, and this all installed over a high quality plastic vapor barrier tacked to the studs and joists. The floors this winter were AMAZINGLY warmer.
Literally caulked and spot painted all the exterior gaps with a good painter in the fall. This closed key gaps around chimney joints to the home, soffit joins to the main living area, etc.
Speaking of chimney, ensure the flues are all closed and even try a piece of foam insulation on unused chimneys that you can easily remove when you use the fireplace. The little updraft from heated area up the chimney is more than you think.
Did the door weatherstipping sides and especially bottom threshold fixes. Found major fails in threshold stipping on 2 doors with mega-drafts... and this was after just 3 years since the entire home renovation. The fixes were less than $15 per door plus some elbow grease.
Put a foam insulation box around the attic ladder access. Just like the chimney, more escapes around that attic access than you can imagine.
Of course, did the filters on the HVAC system and cleaned the fridge coils.
All the above saves ~$380 per year (~$25 for 6 coolish months, $50 for 4 summer months, probably maybe $15 in spring when HVAC isn't used much) and took less than 4 hours all told (except the exterior caulking and painting we hired out) plus the LED bulbs and foam board and door stripping insulation to the tune of $300. 1 year payoff and well over 100% rate of return annually thereafter.
