Then you didn't have the tank system fitted properly because it's easily possible to have a substantial flow.
If your pump makes a lot of noise, you either bought a cheap one or it wasn't fitted properly.
That is demonstrably nonsense. There is no physical way that even quite a large combi system can deliver hot water at a greater rate than a tank storage system provided that the pipework is adequate on the storage system.
If the hot water cylinder stores the water at > 60 degrees there will not be a bacteria problem.
This is complete nonsense.
The rate of water production from a combi is *highly* dependent on the incoming water temperature and the flow rate. This is not the case where the DHW is stored.
Neither will give any significant temperature drop between the point of heating and point of delivery in a normal house.
A combi is suitable for a flat or very small house, or where the occupants have modest requirements for hot water delivery.
For a 3-4 bedroom house wiht multiple occupants, the performance becomes increasingly inferior to storage. Storage can be by directly storing the DHW in a cylinder, or via a heatbank, but is the only way to get good results where multiple bathrooms are in use.
Ok, point taken that I kind of compare unequally sophisticated systems with my cranky old tank. I accept what you say about the flow rate. The problem of limited supply remains. Doing the dishes, taking a bath, taking another bath, and another set of dishes - easy with children.
That contradicts the fact that we all have to boil water to get rid of the nastier bugs. Seriously, 60 degrees needs a fairly long time to kill of most (not all!) bacteria. To kill the lot you need to go above
95 or so. Nice touch about the combi: it produces drinking water regardless of hot or cold water. VERY handy to wash veg in deep winter. Up here in the North it gets really cold indeed!
Of course you are right that the incoming mains temp is the main determinant, but if you look at the installation then distance between boiler and consumer becomes crucial. Same for your tanks, hence having the tank close to the bath.
That will depend on what you call normal.
Yes that is the point. With en-suite being the dream component of an English household I see your point. Nowhere else are en-suites seen as so desirable, but I fully take your point. But to quote you: it's of course nonsense to say that a combi cannot serve a four bed house. Unless you know the customs of the household (shower rather than bath) and the preferences for low heating bills, you cannot possibly decide. Also, with combis, you get what you pay for. The cheapest oldest combis had problems, but the ones I know that have been installed here in the last five years, work great - even in big houses. I accept that the English use the bath much more than our continental neighbours, but for many people the combi works marvellously more or less regardless of the size of the household (there are limits: would like to know the heating system of Beckhams ;-))
I have a 200 litre HW cylinder with fast recovery from the boiler.
I can get 25 litres/minute of 60 degree water for filling the bath, plus the same of cold. You won't get those figures out of a domestic combi.
I can have 25 litres/min of 40 degree water out of two showers simultaneously.
All of this is independent of the cold mains temperature.
Not where I live.
It is what is recommended for control of Legionella etc.
You are assuming that there is a population of harmfull bacteria in the first place. The water in the loft tank is replaced with chlorinated water from the mains as it is used. Most households get through several tanks a day.
If what you say were an issue, there would be massive outbreaks of water borne, disease and poisoning in the UK. There isn't, so it's a non issue.
Why would you want drinking water at 95 degrees?
You wash vegetables in hot water?
Oh dear. First of all this is unnecessary. Secondly it begins the cooking process earlier than necessary which results in many of the vitamins in them being broken down.
No. The only issue between boiler and consumer is the length of time it takes for the water to travel - i.e. how long it takes to get hot water at the tap.
There will be little temperature drop along a pipe run unless the flow is a tiny trickle. Even the poorest combi can manage that.
For significant temperature drop to occur, there would need to be significant heat loss. In calculations for central heating, heat losses from the pipes (where running internally) are not taken into account when sizing the radiator and boiler requirements.
Anything up to a 5 bedroom, 2-300m^2 house - where pipe runs are a few metres internally.
If there is one person living in it and they take showers only, and the combi is a 15lpm+ model, possibly. However, if the house is populated with 4 people and two bathrooms and they take baths and showers simultaneously, in the winter one one be very hard pressed to satisfy the requirement with a single domestic combi.
Exactly. So the requirements of the possible population of the house over the lifetime of the heating system should be the factor. THerefore, for a larger house with two bathrooms, the assumption of a lot of use should be made.
If somebody wants to fit a combi in this type of environment, knowing the limitations, then fine, but they should be aware of them.
It doesn't matter how "great" they are. Thy still can't defy physics.
The basic prinicple of mass x specific heat x temperature rise still applies, and this is a fundamental limitation on any form of instant heating using the fuel supply directly. The only way to improve on this is to store the hot water directly, or via a heat bank.
That would depend on your definition of "marvellously" and how many bathrooms. I suppose if they had used electric showers before, it would seem good.
Even quite large combis can only deliver 15-20lpm of water at 40 degrees in the winter. THis is marginal for one shower, let alone two.
Patronisme as you wish, but don't tell me that it's fun to wash your veg at 5 or 6 degrees cold water. 10 or 15 is much better. In winter, you cannot get this without a mix of water. If you wash veg for half an hour in 5 degrees you will beg for a combi. At least everybody I know with a combi does mix a bit of warm water to keep the fingers from going numb. Assuming that I am washing veg in hot water is deliberate misunderstanding, kind of serves my point really.
You have obvioiusly never taken a shower in a combi system with decent mains pressure to call it marginal. Hence, I recommend case closed, keep your system and I will keep mine or rather I will have mine. Two showers btw is not the issue. I do not question that combis have problems serving two showers. Whether or not your tank system would do it for me is not the issue because I will never want a house with more than one shower, regardless of the number of children :-)
So put some cold water in the sink and add a little hot. From the kettle if you are precious about it.
For half an hour???
Not really. It's just a poor illustration.
Yes I have. It's very easy to create high pressure from a mains fed shower - even electric showers at 4lpm can do it. However, it's only useful and pleasant if there is a good flow as well.
In this regard, a combi, in winter will produce approximately it's rated (35 degree rise) flow at a shower. SInce most that are sold are in the 11-15lpm category, the results are not that great. Perhaps you prefer a needle jet shower; personally I don't - I prefer to have a good pressure and flow.
It is in a larger house with two bathrooms and population to match.
A properly installed storage based solution will provide many times the how water flow rate of the largest instantaneous combi.
Furthermore, a properly installed storage based solution will be able to take the full output from the boiler. This means that over any period of time, it will be able to produce as much hot water as the combi.
To give you some idea, I filled a 725 litre birthing pool to 40C in just over 40 minutes. That's equivalent to a lot of baths and showers.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.