Running a combi boiler along with tankless gas water heater

[Nikki Mikki]

Hi everyone,

We are currently doing a loft conversion and rear extension which will give us 3 bathrooms (3 showers 1 bath). It is very unlikely that we will ever end up using all 3 simultaneously but there is the possibility for 2 showers at once at some point. I must add that the CH will be replaced with UFH throughout the house. The house is 4 bed mid terraced. We currently have a combi Vaillant green iq843 which is about 3 years old and although is one of the biggest available on the market the builder is adamant that it won't be sufficient for 2 showers hence he recommends adding 210l Megaflo to the combi. Our main concern with the Megaflo is the size of the cylinder and after some research, we discovered Rinnai water heaters, especially the N1600i model capable of delivering 35l/min. The general idea is the UFH, kitchen and ground floor shower to be fed via the combi whilst the other 2 bathrooms to be fed through the Rinnai water heater. Have any of you considered a tankless water heater over a Megaflo and if so do you see any limitations in this arrangement? Many thanks in advance!

 

[ianmcd]

Not that simple, all depends on your gas supply very unlikely your supply will be big enough for both

 

[muggles]

The Vaillant is 43kW, the Rinnai is 58.4 kW, total 101.4kW. The maximum you can pull through a standard domestic U6 gas meter is 65kW, so you'd need to get an upgrade to a large domestic U16 meter, which is about the size of a washing machine by the time the enclosure is installed around it as well. You'd also need to engage a commercial gas engineer as the domestic engineer's limit is 70kW.

Have you had your incoming mains tested to see what it can actually deliver? There's absolutely no point putting a water heater in which can deliver 35l/min if your incoming mains is only providing 25l/min, for example