Heating and hot water for granny annexe

pasty_girl

Hi - I'm really sorry if this has been posted before but these forums are extensive!!

We are building an annexe in our back garden, about 20m away from the main house. Two rooms internal dimension total about 32m2. It will be made from a SIPs construction so hopefully very well insulated.

We are trying to work out the most economical way to heat it. Options we are considering are:

1. Electric everything - how much should we expect to pay for 2 electric radiators with timer and thermostat functions?

2. Air con/heat pumps. Probably a split system, so one outdoor unit linked to two indoor. The thing we are struggling with this is how much do they cost to run in comparison to an electric radiator? Then electric shower and hot water for kitchen sink on separate systems.

3. Run an insulated pipe (Uponor style) from the main house down to the annexe and back which would contain hot water for the heating and separate pipe for the shower and sink.

Does anyone have any thoughts on this? We don't want to spend a huge amount upfront if it would take 20 years to make the money back on energy bills!

Many thanks for any insight, or any other ideas.

Cardew

Welcome to the forum.


Is it going to be used extensively and with a regular pattern? like a granny annex?


Presumably the electricity supply will be from the main house to a separate consumer unit, and thus avoid separate metering and a daily standing charge?


It might be worth getting a quote for Uponor pipes and to use the annex as a separate zone on your CH system. If the CH cannot be zoned you will encounter problems on controlling the required temperatures in both buildings. Also every time Hot water is required in the annex you will need to 'run off' a lot of cold water in the pipe - a problem if you have metered water.


Personally for a smallish annex I would be in favour of the cheapest outlay and get panel heaters. Just about every decent heater has a thermostat and you can get each of them wired via timer costing very little. They can be obtained from as little as £100. http://www.dealec.co.uk/acatalog/-Panel-Heaters-ph.html?gclid=CKP-s_Lo9MwCFc0y0wodrOAF2g (I just googled). It will not hurt to get more powerful heaters than necessary as the thermostat will cut in sooner, and the room will heat quicker.


Don't be fooled by the adverts for heaters that produce more heat for lower running costs - they simply do not, all electrical heating is 100% efficient.


For Hot water something like these(I just googled) https://www.aquahot.co.uk/water-heaters/in-line-instantaneous-electric-water-heaters


Will suffice. Don't forget that the larger models will require heavy duty electrical wiring installing and a larger RCB

pasty_girl

Many thanks for this this is really useful.

Yes the annexe will be occupied by my brother so it needs to be heated well and will be used extensively.

We are having the whole house refurbished so the electrics etc can be updated as necessary. Plumbing also being completely redone so we could have a separate zone for the annexe if we went the insulated pipe route.

The links are really helpful too, thank you.

I take it you don't rate the air to air pump (air con/heat pump) idea as a good one?

Cardew

pasty_girl wrote: »

I take it you don't rate the air to air pump (air con/heat pump) idea as a good one?

Air to Air heat pump units are highly efficient, but of course you are going to need to make provision for Hot water.


They can also cause a noise problem, particularly for neighbours(which could be yourself;))