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The East Dulwich Forum
Would you recommend your builder, plumber, electrician or carpenter?
messageWhat on earth is a megaflow?
Posted by motorbird83 27 September, 2013 12:00

Hello everyone,

I'm hoping to tap into the collective wisdom of the forum yet again regarding my loft extension! We are trying to work out with our heating engineer what we need to deal with the additional bathrooms we are adding to the house. The current boiler is 1 year old and in perfect condition.

Our builder has told us that his plumber says we need to chuck the new boiler, get a new larger boiler and get a megaflow.

My question is why would I need both a boiler and a megaflow. I thought a megaflow was its own heating system and that would suffice on its own even if you had multiple bathrooms. Also, even if you wanted a back up boiler, surely the one that could heat the house adequately pre-extension should suffice :/

Very confused as I think the plumber might be overspecifying the house. Right now its still just me and my husband. We had a Woscester combi in our flat which also had two bathrooms-- though in the 7 years we lived there I don't think we've ever used both showers at the same time. I can't see the multiple shower thing being that big of an issue until we have older children and given we don't have any yet, whatever we put it might need replacing by the time its of any use!

If there is anyone who's done a loft and had to work through any of these heating / plumbing issues, your thoughts would be very welcome!

messageRe: What on earth is a megaflow?
Posted by BellendenBear 27 September, 2013 13:02

We had building work done last year and were advised to get a megaflow. We moved our kitchen and boiler into the basement and were told that a combi boiler wouldn't be able to hear the whole house plus enough hot water for 2 bathrooms. This means that we have a massive tank with the boiler.

messageRe: What on earth is a megaflow?
Posted by bluesuperted 27 September, 2013 13:17

We just did a loft conversion and got the hideously expensive megaflow system plus new boiler (but different brand, not actually a megaflow but same thing). Our 2 bathrooms now have great heat and water pressure and we were advised it is a good selling point on a 3-storey house. We spoke to 3 loft companies who had varying thoughts on this but we ended up trusting the ever-helpful John Powers (oft recommended on here) and he guided us through the decision-making process.

messageRe: What on earth is a megaflow?
Posted by motorbird83 27 September, 2013 13:23

Very helpful. I'm trying to read up so I don't get lost in technical jargon once I finally speak to the heating engineer. Dear I ask how hideous is hideously expensive?

messageRe: What on earth is a megaflow?
Posted by scareyt 27 September, 2013 14:51

I obsessed about this very question for months before we did our loft! In the end we kept our recently upgraded boiler and replaced our old hot water cylinder with a megaflo. Basically, the boiler heats the water and then the megaflo stores it and feeds it to your hot water taps at high pressure.

If you can upgrade your incoming mains pipe to 22mm the megaflo works well. (Old Victorian mains pipes are 15mm). We didn't upgrade our pipes because we have a solid tiled hallway floor that we didn't want to rip up and ours works ok but not perfect. I only notice it when running a bath, but at first the hot water comes out super fast and then it gradually slows down because the incoming mains isn't filling it up as fast as it's going out. We thought we would upgrade the mains if we ever do any work on the downstairs of the house but I'm used to the hot water now and it doesn't bother me.

Some plumbers recommended an accumulator to feed the megaflo but I'm glad we didn't bother with that now. That's basically another tank you can put in the eaves with a rubber diaphragm inside it that maintains the pressure to the megaflo if your incoming mains is slow. It replaces the effect of the old cold water tank in the loft that created pressure through gravity.

messageRe: What on earth is a megaflow?
Posted by motorbird83 27 September, 2013 15:15

Thanks, that¡¦s really helpful. I¡¦ve been reading that it might be possible for me to link the megaflo to the existing (and brand new) combi boiler installed by the previous owners via controls. If you only get the megaflow cylinder and link it to your existing boiler I imagine that helps reduce the costs as its only one new item being installed rather than two? Our house is a shell¡Xthe only thing that had been done to that place in 50 years was changing the boiler- so upgrading he mains pipe isn¡¦t a problem. For me, my main concern is cost. To be frank, I don¡¦t think we¡¦ll run into the shower issue for years to come so as long as there is enough capacity to heat the house and run one shower, I¡¦ll be satisfied ƒº

messageRe: What on earth is a megaflow?
Posted by scareyt 28 September, 2013 19:50

I'm not sure if there's any point having a megaflo with a combi boiler because that boiler heats the water instantly as you use it so shouldnt need storage for the hot water. Maybe thats why plumbers have suggested changing the boiler. You could always stick with the boiler you have and just get the builders to make an airing cupboard big enough to fit a megaflo with the right pipes running through it so you could change the boiler and add a megaflo later if you want to? Our existing first floor airing cupboard with the old cylinder was too small and we didnt want to rip that bathroom up so we had a big cupboard put into the loft bathroom to fit the megaflo. But I think if you plan a space to put it in later you might be able to avoid the cost of it now.

messageRe: What on earth is a megaflow?
Posted by scareyt 28 September, 2013 19:54

Although you might then have pressure problems, not sure. Some plumbers said we could avoid the pressure issue by just installing a pump in the first floor but others said all pumps are a bit noisy I didn't want an extra weird noise in the house. We must have spoken to 6 plumbers at various times and they all recommended something different!

messageRe: What on earth is a megaflow?
Posted by motorbird83 30 September, 2013 11:53

Update for those interested. I spoke to my heating engineer and he confirmed you can fit a combi to a megaflow. The combi heats the water in the megaflo cylinder when you program it to but you can prioritise using your combi boiler for most of your heating needs. It's actually the best of both worlds as you still have the benefits of a combi (instant hot water from the mains / using less energy) but with back-up stored hot water when you anticipate needing it. You only need the megaflo reserves for when hotwater demand exceeds what is provided directly from the mains (which apparently is what combi boilers heat directly assuming your combi-boiler is powerful enough to heat all of the mains water of course). That's why pressure drops on a combi when two hot taps are running simultaneously. I think we'll only need the heat the back-up water in the megaflow when guests are visiting or very early in the morning if we both want to shower. The rest of the time, we'll just use the combi.

I know more about heating than I ever thought I would...


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