Hot Water System for Granny Flat

Buddha Breath

Hi Folks,

I'm converting a large room in my house into a granny flat and am considering different options for providing hot water to a bathroom and kitchen sink. The main house uses OFCH and we have a small HWC that's approx. 25m from the proposed granny flat bathroom\kitchen. Due to the small size I don't think the existing HWC will support the extra load so am looking for alternatives. We also have an existing electric shower in the house. I also think it would be useful to have the granny flat more independent, i.e. with it's own hot water system. The granny flat's heating will be provided by the existing OFCH system for now. There is a large attic space above the granny flat. The hot water requirement would be to cater for 1-2 showers per day and occasional dish washing. I'm currently considering the following options so would appreciate any advice based on experience or am open to any alternative suggestions.

1. Install 50 or 80L electric tanked water cylinder in flat or attic above (mains fed)
2. Install gas instant water heater in kitchen unit in flat, with either bottled gas or additional installation a LPG tank outside

Many Thanks,

Alan

DublinDilbert

I would make a hot-press and install a small insulated copper cylinder, if space permits. You could allow some of the flow from the central heating system into the cylinder to heat the water and then have an immersion element to top it up. Keep it all standard and straight forward, maybe provide a boost button for the immersion so they can boost the immersion if needed.

zg3409

Water from a hot tank with a pump to a shower will give a much better shower than an instant electric shower particularly in winter. If you don't want a hot press attic may be an option and feed from attic tank in main house. If you want attic tank in granny flat then it needs to be higher than hot water tank.

In terms of space heating allow a method for "granny" to heat accomodation themselves. Either electric heater bolted to the wall or a way of turning in main house heating with a zone for granny via a timer or boost button. At least do the zone and wiring run. Consider internet and tv too, maybe run tv and internet cables.

You can have two instant showers but one needs to have priority as both can't be in at the same time. Easily done but not as independent as you seem to want.

Beware running everything from electricity as it's more expensive than gas heating typically for space heating and water heating. Make sure to in insulate well as granny places have a lot of external walls and tend to get cold quick. A combi type gas boiler is probably too much but it can instantly heat hot water for a shower without a hot tank needed.

Buddha Breath

https://www.boards.ie/discussion/comment/120305461#Comment_120305461

Thanks for the response. I wouldn't really have the space in the flat but could install in the attic space above, I suppose. I was hoping to avoid digging up the floor to install additional pipes and zone valves to keep costs down. My initial plan was to do as you suggest (keep it standard), but seems like a lot of extra hardware (expense) to do this. Hence looking at alternative options like the electric (not instant but 50L storage) boiler in the kitchen press (or attic).

Buddha Breath

https://www.boards.ie/discussion/comment/120305495#Comment_120305495

Thanks. I'm considering a gas water heater (not a full combi), to heat the water. The other alternative is a 50 or 80L storage tank (electrically heated) that would work at mains pressure. These don't seem to be very common in Ireland but are used extensively in Europe and the US. Something like this

https://www.ariston.com/en-uk/products/electric-gas-water-heaters/electric-storage-water-heaters/velis-evo-wi-fi/

Was hoping to hear from anyone who may have one of these installed to determine whether they are relatively economical to run, and whether the water pressure is OK for a shower.

seanjpm

I've installed a good few rinnai 17e, great job, perfect for what you're looking for. Plank it outside the granny flat and it'll provide hot water all day. I installed a few that fed 3 showers in a communal area and never had any issue with them. You can run them off a 34kg propane tank, very economical. As long as you've a respectable mains water supply it'll run fine

https://shop.calorgas.ie/rinnai-infinity-17e-35kw-external-lpg-gas-water-heater.html

Buddha Breath

https://www.boards.ie/discussion/comment/120307114#Comment_120307114

Thanks Sean, that's good to know. Could you put a number on "respectable" in terms of mains pressure? Could a circulating pump be used in conjunction with one of these?

seanjpm

It'll run on a minimum of 0.8-1 bar so you should be alright almost anywhere in Ireland. If you've never complained about the mains water at your kitchen sink you're pretty much alright, they aren't hard to run. Only thing is you'll need someone RGI to install it and commission it but whoever you get will check your water supply be installing.