If water heater tank is 7-8 years, and going to reno, shall replace the heater tank?

Depends and up to you. If you think good opportunity to replace then just replace it.

It's not everyday we get a reason to replace something.

if the reno is extensive, would recommend to change it. Water heaters are typically up in the false ceiling and leaks will happen when it hits close to 10 years (mine leaked at 7 years). then when it happens, you may not even know until a patch on the false ceiling is noticed.

Thank you guys. maybe it is time to replace it

If you're looking to replace it, I'd recommend an Ariston storage heater, we ended up still concealing ours in the reno so it would be cleaner but in case you want the option, I still find their designs the most modern and unobtrusive of all the options. Going on 5 years and we're still happy with ours.

http://bq.sg/2015/05/27/instant-water-heater-mid-year-promotion-ariston/

Saw this Ariston promotion and I suddenly thought of this discussion thread, is it a hint that its time to change our water heaters?

Generally me and my husband feel that water heaters are not very expensive compared to our health. Like the heater in my parent's house, it rusts after 7-8 years. So we decided that to be safe, we'll change our water heaters every 5-6yrs. Keeps the moss/ rust away from our showers too