When you say you're careful not to overwater, what exactly do you mean (how do you water, how often, and based on what signs from the plant)? Plus what kind of soil is it growing in?

If you've only had it two weeks, it may just be reacting to the change in conditions. I'm not sure which plant you're describing, because there is an actual Philodendron with heart-shaped leaves (P. hederaceum) that are green and yellow (P. hederaceum 'Brazil,' or sometimes 'Brasil'), and there's also a more common plant, pothos (Epipremnum aureum), that has heartish leaves which are green and yellow and is often mislabeled or misidentified as a Philodendron. The petioles ("stems" which connect the leaf to the main vine) on Epipremnum have a prominent groove in them; Philodendron petioles are smooth. Philodendron leaves have fairly broad chunks of yellow, usually in the center of the leaf, and a few deep, prominent veins extending to either side of the center vein; Epipremnum has smaller, more uniformly-scattered yellow patches, and no prominent veins besides the center one.

The prescription in either case is more or less the same.

1) Don't panic. This is probably temporary acclimation to your home, and not a sign of anything serious, especially if you've only had the plant for a couple weeks.

2) Warmer temperatures. 60F is more or less the low end of what's permissible for either of these plants; Epipremnum is more touchy about it in my experience. If you can raise the temperature to around 65F (good) or 70F (better), this will help. If not, moving the plants closer to the ceiling will give them a little bit more heat than they would otherwise have.

3) More light and humidity. Probably not strictly necessary, but these would ease the transition. Humidity, in particular, will help, if your home is not ordinarily humid already (if you're in coastal WA, this is probably not necessary, though more light is still a good idea. If you're in inland WA, you probably need to worry more about humidity than light.).

4) Water. Both these plants do better if they're allowed to get pretty dry between waterings (like, you should be able to stick your finger down into the soil without hitting anything moist, before you water again). Epipremnum in particular prefers not to be fussed with too much. If Epipremnum is too wet, leaves in random spots around the plant will yellow and drop; Philodendron is more methodical, and works from the base of the plant outward to the growing tips.

5) Time. If it really is just a matter of acclimation to your home, this will come to an end naturally within 2-4 weeks.

Mike, yellowing and leaves that turn brittle do have particular causes and while it may be normal due to changes from the place you brought it from to your home, you should still be aware of what can cause such conditions.

Make sure your pots drain well and use water that has been allowed to sit overnight to gain room temperature. Plants can be stressed when given water straight from the tap if it is very cold. When you water, do give it sufficient to show it is draining. That necessitates having a saucer or catch-all for such drainage. Since your plant is one that hangs you will have to provide either a type with the catch-all included in the pot or bring your plant down, water it to drainage, allow full drainage before you dump the excess and only then return it to its hanging position.

At this stage of the season the sun is very low and will not gain strength until mid February. Even tho phils can take less light. the plant can be given pretty well what sun you can provide by putting it close to the window.

Yellowing can also come from too high a nighttime temperature. Daytime temps of 60ºF are a bit lower than they need but still, plants do appreciate lower temps due to their not taking up as much water as they will when conditions improve.
And since they are not growing as they can, they need much less fertilizer.
Any degree of 'too much' sun, fertilizer, water...or too little of the same can result in leaf edges turning brown.
Once you get to know how your plant behaves with what care you give it, it will adapt and give you many years of delight.

Thank you all for your help! I will take all this in and see if it makes a difference. Mike