I will probably be going against the grain on here. I have a large house that has about 12 rooms and a large hallway. I have 3 bathrooms (2 showers) and 17 rads. I have a combi (Baxi Duo Tec 40 HE) - this was my first ever combi and I have previously had normal heating systems with a hot water tank and a megaflow system.
This is the best system that I have used and am delighted with it. Granted if I am in the shower and the washing mashine is on and someone flushes the toilets you will feel the pressure drop. However, it is just a pressure drop, the temperature of the water has never ever altered.
I think we are lucky in that according to the last plumber that serviced my boiler the key to a combi working well is reasonably good mains pressure. The power I get from my combi showers is as good as the megaflow system but the real benefit is that it is the most efficient system that I have ever run and I have hot water whenever I want. The megaflow at the end of the day is a cylinder that runs out of water.
Not by design but we tend to run appliances such as washing machines and dishwashers when we are up and about and not when we are showering and we rarely find a situation where both showers are running at once. There may be some slight adjustments such as those that people may need to make for a combi to work, but I firmly believe it is worth making those adjustments for the benefits that it offers.
Just my opinion and as I say there will be many on here that disagree with what I have said here, but it works for me.
Got a similar recommendation off another forum:
" I have 5 bed 3 bathroom 3 storey house. I turn the hot tap on and hey presto hot water. I have 3 thermostatic showers, 1 bath, 5 sinks & 2 outside taps.
Don't understand people that seem to think cylinders are the best thing since sliced bread. When realistically are all these going to be used at the same time? Even when i am the bath still fills with hot water, the showers still run without the need for you to run around in it and people can still wash their teeth.
My gas bill for the 3 months this summer was £15. Yep £15 i can post a pic if you want. I have a gas hob also.
I have 8 or 9 rads and 3 towels rads. Ill be adding 2/3 more rads in an extension soon and it'll all run off the same boiler without problems or incident I'm sure. P.S. its a Vaillant 837 so not massive.
Any registered gas fitter that "tells" a customer a load of nonsense shouldn't be in the job. Don't believe the hype. Forgot to mention....they're probably the same ones that say you need a "powerflush"!"
The funny thing is, I have hardly ever heard anyone say, "You know, I got this system, and it was a let down, I recommend you get something else".
What does this mean?
Perhaps that most people make do and find happiness with whatever they buy.
And perhaps.... that....
Both Combis and Megaflos can work in 4 beds and bigger?