It's been a while since I've visited Folsom, but if I remember correctly it can get pretty darn hot during summer, but it's mostly a heating climate.
- In other words, you should prioritize your investments towards items that will keep the house comfortable during heating season.
- But many of those same investments will help keep the house cooler during summer.
Since you mentioned wanting to phase the projects over multiple years, I will recommend this order of priorities.
R50 is a great insulation level and cellulose is a great material.
The reflective foil you mentioned is a radiant barrier and I'd say it would be helpful, but is most likely not critical unless you have had major comfort issues in the past.That being said, if it is relatively cheap to add, you might as well do it now.
All houses need a certain amount of air exchange to maintain healthy indoor air quality (IAQ). Houses need to be able to exhaust moisture, combustion byproducts, cooking fumes, etc. and they need to bring fresh air inside.
- The national standard for "ideal" is 0.35 Air Changes per Hour under natural conditions (aka 0.35 ACHn).
- This means fully exchanging the air in your home roughly every three hours.
The blower door test result would have indicated that your home is too tight, and since you have seven people living in your home, you would need a higher-than-average amount of air exchange to maintain healthy IAQ. The more people you have in a home, the more air exchange is needed. If that doesn't make sense, please let me know and I can explain in more detail.
Thus, ventilation is a matter of health and safety and should be dealt with asap.
Heating and Cooling System
Ductless Heat Pumps (DHPs) are hyper efficient and can do a great job heating and cooling. However, it is important to make sure your house is well insulated and properly ventilated first so that they can work properly.
- Also, make sure the system is designed and installed properly, specifically regarding having enough indoor units (aka "heads") mounted.
- I have seen quite a few systems undersized since they can be relatively expensive upfront.
I'd suggest confirming that you do not experience many nights below 17F ambient temperature since the heating function may not work well below 17F.
The above three projects represent what I define as a great "basic performance upgrade". It addresses the major comfort, health, and efficiency items. However, it is also good to consider high efficiency water heating, lighting, appliances, etc.
Please let me know if you'd like any more information regarding additional home performance projects.