Thanks for your interest.
The Granny flat is detached, but for simplicity I would rather run all services from the main house - unless there are major benefits from having them separate?
Divide and rule really. It could become a rented out place in future.
Liked the Megaflo video - but that sounds a bit like someone selling me critical illness insurance i.e. if it's properly maintained/serviced it shouldn't happen.
That is what they can do when the safety devices fail. They can take down the side of a house.
Megaflows require an annual service which costs, just to store water.
However, I am very interested in any other options to the Megaflo. Can you please explain in laymens terms the difference/benefits of the other system you suggested.
A heat bank does the same as a megaflow but is
failsafe and can operate on higher cold water mains pressures. No power shower pumps and other tripe.
A heat bank can also do the CH as well. The rads are run off the heat bank cylinder. So this means three CH circuits can be run off the heat bank. One for downstairs one for up and one for the flat. A Grundfoss Alpha auto speed pump on each and TRVs on all rads. No wall stats. In the flat a simple time clock to switch in and out the pump and boiler/heat bank. Same with the other two heating zones.
The boiler when heating a heat bank is operating in an ideal hydraulic environment. They heat up efficiently in one long efficient burn.
If I was you, I would go for a heat bank/thermal store. Have three CH zones off that. TRVs all around the rads with each CH zone having its own timeclock (upstairs can be switched off and downstairs on during the day) and have a DHW secondary circulation loop.
Take the heating to the flat in a large plastic buried pipe filed with vermiculite and the pipes with heaving insulation taped to them.
Make sure the cold mains is good enough and replace the stoptap with a full bore tap. Have an isolation tap on the gas and water to the flat inside the flat.
A heat bank may have backup electric immersion that do the DHW and CH.
Insulate the hell out of the flat and the extension, like 8 inches in the walls over 1 foot in the loft.
