Are there any luggage storage facilities in Hanoi Airport (Noi Bai)? If so, how long can one store items for?
There is a facility on Terminal 2 on the upper floor (as already mentioned in the other answer).
They charge per block of 3 hours and then per day up to 30 days, although the rate changes after a week. Count below $4 per day, you pay in VNDs though.
Your luggage must be locked, does not matter if it has zippers or not but they want to see a lock or they will refuse to store it. It is not written anywhere but that is what I was told by the attendant this year. It seemed like a secure place with a guard 24 hours/day.
I used WhaleLO luggage storage last month when I came to Hanoi city with my family. We got a lot of luggage and had to wait until check-in time. I stored 4 hours and just costed me about 3$ for my bag. For me the price is reasonable and the service is professional. You can find more information about the address, and price on internet. Its store is in 49 trang tien.
My locker service with quite large locker (10-12 year old kid can fit inside) newly introduced in Aug 2018. Largest luggage size to fit in is size L. There are double height/ double depth lockers too.
There are cameras and staff all the time and it's open 8:00-22:30 everyday including most holidays. Actually it's located inside a cafe called Tang Tret Cosmo Cafe on the street of embassy (#10 Khuc Hao) so it is quite safe. $50 guarantee limite on each locker, seal on locker (guests sign on the seal). Hope it helps :)