Combi or Header Tank system

[Edd1056]

Been living in a house (was new) about 16 years, we have a header tank system, but the heater will need to be replaced soon. The miss's wants to swap out the header tank and get a Combi (Prob Baxi 630) installed - We have three story house, one bath room, one on suite and 11 Rads, I am a little reticent about swapping this out.

Pros - on demand hot water, possible increase in water pressure (have a pump in the loft to increase it for Hot water currently)
Cons - the increase in pressure (low to high) might cause a few issues with internal pipes (and leaks), using the hot water doing the dishes will vastly impact on the shower when its used at the same time.

Question to the group - in your opinion is it worth swapping these out - we will get a little more storage space.

I spoke to one plumber who said - best thing you can do is swap it, yet another said, dont swap it, most new builds are not installing Combi's in big houses are they are not efficient.

 

[ChrisJP]

Why does your missus want to go for a combi and get rid of the header tank?
Vented header tank radiator circuits have served us well for many years and contnue to work well. Unvented, pressurised combi boiler systems don't seem to me to offer any real advantages (though I'm sure I'll soon be "advised" of them!). They subject radiators and pipes to increased pressure which may cause leaks in older systems, and are generally restricted as to what a DIY owner can do with them.

 

[vulcancontinental]

Cheaper to rely on gravity, less maintenance and your pipes are the right size. Just upgrade the cylinder and make sure yoou have a Bylaws kit on the CWS cistern.

 

[Mottie]

Has anyone checked you water pressure and flow to see if it’s suitable for a combi? Also, where will the boiler be situated? Probably okay if on middle floor but if on top or bottom floor, it will take an age to get hot water to the top or bottom of the house. My mate has a combi in his loft. They boil a kettle or wash up with cold in their kitchen because of the time it takes for hot water to get to the tap and then you waste all that hot water that remains in the pipe when it cools down.

 

[ericmark]

My old house we removed the cylinder and used the room as a forth bedroom, it resulted in taking longer to get hot water to taps, and took an age to fill the bath, but gaining the bedroom it was worth it at the time.

This house still has a cylinder, which means we can use spare solar power in summer to heat the DHW but hot water pressure is lower.

You do seem to understand the pros and cons, but much is down to how much hot water you use, and if some time in the future you are likely to get solar. A 40 gallon water tank can store 14 kWh of energy, to do that with a battery would cost a lot of money, my battery is only 3.2 kWh, so with 14 kWh the sun could not shine for 3 days and you would still have hot water.

However my immersion heater only heats up top foot of water, so it does depend on your set up. I find with oil I use around 3.8 kWh to heat the DHW and with electric around 0.7 kWh, due to heating boiler and pipe work, with smaller pipework required with a combi boiler the losses can be reduced, but often the old large bore pipes are left in place.

 

[bernardgreen]

For what it is worth

My choice was a heat only boiler and cylinder with a "shower coil"

 

[Madrab]

Depends on what you want from the system

If your cold mains will be suitable, a combi will still struggle with more than one hot outlet open at a time unless the HW system is well tuned using water saving outlets etc. Gas will supply normally needs to be upgraded

Open vent gravity is a tried and tested system. You already know it needs pumped to increase the HW pressure. Your system can be updated to a modern HO boiler without issue as long as the current system is nice and clean. HW options are several, depending on your cold mains dynamic flow and pressure. Very DIY'able.

 

[Murdochcat]

If you think you might add PV in the future you could get free hot water and help reduce emmissions