Choosing the right boiler and heating system

Joined
26 Jan 2020
Messages
44
Reaction score
0
Country
United Kingdom
Evening all, I'm after some advice/guidance.

I'm refurbing my 2 bed bungalow and will be extending it in the near future. I need to replace my heating system but I'd like to understand my options and requirements before I engage with an engineer. I've tried to do some research but I'm relatively new to this area so if I've misunderstood anything, please correct me!

The renovation & extension will see up to 9 additional radiators, a second bathroom/shower and a utility room with a shower specifically for the pooch.

One engineer suggested a 30kW combi based on my plans for the extension, but I've since read that even a high powered combi may not be able to cope with multiple showers; and whilst I live alone and its unlikely more than one tap or shower will be running simultaneously, I don't want to have to replace the boiler prematurely should the demand increase!

I'm therefore considering a system boiler with unvented hot water storage. Alternatively, a combi for now, which I've read can be 'converted' to use an unvented cylinder in the future. Used in this way, would a combi boiler still be efficient?

Either way, how do I ensure the boiler isn't oversized? I've calculated the future heating requirement at 13.6kW (although it's an older 60s property so it could be a little more.) I'd prefer to have a lower flow/return rate (to ensure the boiler actually condenses) so I plan to oversize the radiators to compensate (adjusted for Δt40).

This may seem a stupid question, but should the boiler meet the heating requirement for the house (13.6kW) or does it need to meet the total output for the oversized rads (18.2kW)? What about the cylinder? Should this be included in the kW output? How do I calculate this?

Thanks for any advice - like I said, I will be speaking to an engineer - I just want to make sure I have enough knowledge so I don't get sold something that isn't suitable or oversized.

Art
 
Sponsored Links
You need to find out your mains pressure & flow rate before making any decisions. An unvented cylinder will be pointless if your water supply isn't up to the job of running it. Having said that, if it is then it would certainly be the best option. The boiler should be sized for the heat requirement for the house, although you can get away with it being a bit bigger without massively affecting efficiency. Run a hot water priority system and you don't need to make any allowance for the cylinder - the boiler will switch over to heat that up quickly as required, then return to doing the heating.
 
The renovation & extension will see up to 9 additional radiators, a second bathroom/shower and a utility room with a shower specifically for the pooch
There are some very strict requirements for showers for dogs , you might want to re-think that one , will be extremely expensive and the fines if you get it wrong are eye watering
 
Thanks for replies!

The flow rate is 19-20ltr/min. I'm not sure about the pressure, I've ordered something to test the pressure with. What's the threshold for when an unvented cylinder no longer becomes a viable option?

There are some very strict requirements for showers for dogs , you might want to re-think that one

I hadn't considered that a 'dog shower' in a domestic setting would be regulated. Out of interest, are those regulations for animal welfare (temperature?) or for water supply/sewerage contamination? Getting slightly off topic, but what's the difference between me taking my dog to 'my' shower, or using one I've set up on a platform so I don't need to bend down?
 
Sponsored Links
Hi,

So my pressure is about 5.6 bar, flow rate 19-20 ltr/min. Would this be suitable for an unvented cylinder?

What about the option of starting with a combi, and switching to a cylinder at a later time should the need arise? Is what I've read about combi boiler being used as system boiler correct?

Or, would I instantly see the benefit of an unvented cylinder, even with just one shower/tap running at any one time?

Thanks
 
5.6 bar pressure but 20 litres per minute flow rate sounds like a pipe restriction somewhere. If you attach the pressure gauge to your outside tap, then turn on the kitchen tap, what pressure reading do you get with the kitchen tap running? Is your stopcock fully open? If you open a second mains-fed tap, does the flow rate from the first drop away?

On the basis of your initial readings I'd suggest going for an unvented cylinder, and finding out why your high pressure isn't translating to a higher flow rate. It could be a mains restriction, or just a restriction at the tap you're measuring from
 
Thank you muggles.

Stopcock fully open. No pressure drop when one or two taps running, but flow rate on one tap which I only get 10ltr/m from anyway) slows a little when another is turned on.

It's 15mm pipe from the stopcock to the outside tap (where I'm taking the flow rate from), but it's very old pipework and I'm not discounting the stopcock being jammed. Also in a very hard water area - could limescale build up in the cold water pipework and cause a restriction?
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Back
Top