Same as I am seeing.
Thanks to some advice from onq here I have sorted out my water storage tank insulation. The insulation should go all the way to the floor of the attic, mine did not.
Heat was prob getting into the attic space because of this, will keep an eye on things and see if there is any improvement.
These are two different but related issues.
1. Allowing heat from below to rise in a controlled way to prevent the water tank freezing.
2. Reducing water vapour in the air sufficiently enough to let the ventilation provided clear away moisture forming on cold surfaces.
The relationship is that warm air holds more moisture, ready for deposition on a surface which is below dewpoint temperature.
Unless you know everything about the building physics of a space its difficult to predict what effect correct tank insulation may have.
Factors to consider might include:
i) Will the increased heat in the tank water lead to a greater rate of evaporation into the attic space?
ii) Will the closed cell insulation board above the tank prevent movement of the evaporate enough to ensure there is no greater contravention?
This is an extreme, and somewhat marginal, example.
Such issues may be irrelevant to well vented older houses regardless.
The effects of attic venting may be more of an issue with sealed, highly insulated homes.
If that is the case, do not be surprised to see matters like this rearing their heads more often.
Yes, there are sealed systems for heating [still needing an expansion tank IIRC] but AFAIK the main tank volume cannot be sealed.
It has to allow for draining at a rapid rate and filling at a less rapid rate, which would displace air in any sealed tank volume.
If it were sealed, it would probably need an external supply air or some sort of diaphragm system.
As you can see, its not a simple science.
ONQ.