check thr air-flow around the windows especially the sills.

I once lived in a cheap townhouse built in the 70's. I was doing some cosmetic upgrading and replacing the baseboard in the entire place. When I took off the baseboard I could see light from outside, so I stuffed fiberglass and/or Great Stuff in there before I put the new baseboards on. I hope that's not your problem, but you might check. I also had a LOT of air coming in through the outlets.

This house has those baseboard radiators on all of the outside walls, so I can see the outside wall under them. I don't see any detectable light, but somehow water is making its way inside. Guess I could get out the spray foam insulation and put a bead all the way around just in case. It's actually pretty easy access.

I did the foam insulation around all of the windows last year before putting in the replacement windows. The candle didn't flicker at the window level. It just went nuts when I put it on the floor.

What do I do about the outlets? Can you jamb insulation around the electrical boxes, or does that create a fire hazard?

I have a close to 40 yr old ranch and it has "rock wool" battes in the walls that are crumbly and cracked apart. My wall insulation performs poorly. What I did was thicken the walls to 6" (actual 5.5") and put new insulation and a vapor barrier. Also replaced windows. I did this in all our bedrooms now and it has made quite a difference. It ends up being a fairly extensive project if you replace the windows but it is worth it. Go to the link below to see details.

Here is a link that might be useful: Adding Insulation To Walls

I posted this in another area or the forum. I'll post it again for those who may have missed it.
Your windows are only part of a very complex system... your home. Every home is different and every climate doesn't care... it just does what it does. The neighbor next to you in the same model home might change windows and save 50%... and you might do the exact same and save nothing. It might not make sense.. until you apply science.

Energy is heat and follows it's own laws. It's laws tell it to move to a lack thereof by any vehicle available. Air transfer is the easiest but many others are readily available in most homes. Conduction, convection and radiation are the primary taxicabs. If your neighbors home is properly insulated and airtight, the energy might have been primarily using the old windows as the vehicle to move in or out. If your home isn't, new windows will only tranfer the energy to the next cab... like your walls or roof.

Think (ATM) = money. Air, Temperature and Moisture always move in relation to each other. If you address one and not the others, they will bring it along for the ride anyways. A typical 2,500 square foot home has over a half mile of cracks and crevices in it's shell. Insulation defects DOMINATE the thermal performance of any assembly. If the insulation in that shell has even 5% of gaps or openings, it reduces the entire shell's insulating value by up to 70%!!! The effect is even worse with higher initial R-values. The air takes the energy for a free cab ride and steps on the gas. Heat does not rise, it moves equally in every direction. Only heated air rises when it is not driven in another direction by predominant pressure or airflow.

If your house is well insulated and very airtight, then your windows might be the primary source of heat loss/gain. Changing these windows with a well insulated and airsealed product might make a huge difference in your energy bills. This would be the hope of everyone going through this process but it may also have very serious side-effects. If your old windows were a considerable source of air-infiltration, the reduction of this airflow will induce a negative pressure inside the home and may cause your cumbustion appliances to backdraft Carbon monoxide (CO). I have personally tested and witnessed this occurance by simply turning on a clothes dryer or a few utility fans. That was all it took to change the airflow. If a shortage is measured, the necessary amount of "fresh" replacement air can then be supplied by controlled mechanical ventilation.

When you change any part of a structure's thermal or pressure boundaries with windows, siding, roofing & venting, etc., you have changed the rules and allowances. It is for these reasons and many more that I strongly recommend having your house professionally tested before and after any shell remodeling. The analysis fees are usually deductable from the contract amount of the work performed. These testing procedures are supported and recommended by the EPA and the USDOE and information can be found through their sites.

The primary objective is to save energy and improve comfort and air quality in the home. This can be achieved in almost every home in America... if you, Test... Before you invest.

Good post window guy! Thank you for re-posting,
this time I saved it!
You are right on track.
Testing home prior to any work to find
leakage sites & after to catch any missed
areas is the best way to 'tighten'a house
and improve efficency & comfort.
Having you home tested with a blower door
is the way to determine where & how to seal
leakage.
Caulking is an excellent sealant, inexpensive
& a DIY job.
Use caution with foams that over expand and
can do damage to home, fire ratings are also
a concern with these materials.

Best of luck with your project.