@Anne - I don't believe you
@Anne, I tried re-doing your calculations. I firstly put 70l of water into my bath (eight year old house), and it was about 4" deep. I normally would use twice that depth. let's ignore the fact that the bath slopes outwards, and call it 150l for a real average bath.
Also, the water temperature measured as 9.8C, not 15C.
So, going by your 90% calculation, we get: (140000 * 4.2 * 25.2) / 0.9 = 16.5MJ
I have two TVs in my house. One, an elderly Sony, claims 0.8W on standby. Another, newer one just says "less than 1W". So let's call it 1W, just to keep the numbers simple.
Using your same calculation, I get 16.5E6 / ( 1 / 0.35) = 5.775 million seconds. That - by your calculations, which I am happy to accept, is 66.8 days of standby time for gas-heated water or 200 days for electrically heated water.