Recommendations for New system boiler in a new house with Evohome

Hi,

I am looking to get a new system boiler installed in a newly built home and looking for recommendations on boilier brands, installers in Surrey. Any help will be gratefully received.

Property information:
The house is a 5 bed detached property (1 of 5 bedroom in the loft) - newly built with current insulation standards.
Ground floor will be wet underfloor heating (4 zones)
First floor and Loft will be heated with raidators with standard TRVs (total of 5 radiators).
The property has 3 bathooms (1 bath + 2 showers : these will be heated by Warmup electric UFH)

Builders recommendation:
The builders got one of their guys in who have recommended a Vaillant 637 boiler along with a 300ltr Megaflow storage tank. The setup is to be controlled by the NEST 3rd generation system

What I am looking to get:
From reading online forums, I've gathered that the Evohome is a better system for my kind of setup (UGH on ground floor + radiators on 1st floor). I also like the fact that Evohome is modular so can be expanded in phases + it is Opentherm.

What I'd like your help with:
1. What size of boiler I should be looking to get?
2. What brand of system boiler would work best with Evohome (with an Opentherm bridge) - so far I am split between Ideal Vogue, Intergas, and Vaillant (although Vaillant wont be OT compatible out of the box without VR33)
3. What capacity of storage cylinder would suit in this situration - I am thinking Haatrae Sadia
4. Are there any recommended installers for the boiler + Evohome setup in and around KT13 in Surrey?

@Mike_W would be a great person for you to PM about this one. Evohome is great but you do need an experienced installer.

His company aren't bad boiler engineers either

I'd be surprised if you need a bigger than 30kW boiler for that. Remember with Evohome it's the minimum modulation that's important as you could end up with just a couple of rads being on!

Thanks for the tip Razor900 - I will get in touch with Mike.

Re. the 30kW size - that's what I was thinking - with the amount of insulation that has gone in (due to building regs.) and the effect of UFH on ground floor - I think the 36kW (as recommended by the builders) may be an overkill.

By the way I have also read good things about Atag boilers and they are Opentherm - so may work well with Evohome (unlike the ER33 required by Vaillant).

Firstly, within all the data you seem to have omitted the size of the house, ie the floor area. This has a large effest on the boiler sizing.
Have you designed-in a south facing roof for solar pv panels? Again this will benefit you (and my children) in the longer term.

I would suggest that 36kW is way oversized for a new-build, but my experience of most 'builders' is that they are so fearful of undersizing that they go for a 'safe' high output, then go a size larger still! There are a couple of 'whole house heating' calculators on the internet, if you put your data into one of those you may well be surprised that the result is that a lower power boiler is required than you have been led to believe, perhaps 24kW or even as low as 18kW.

I won't make recommendations on boiler brand, but simply try to impress on you the importance (to future generations and future pensioners too) of buying something made in the UK. I know I bang on about it regularly, and have been doing so for the last 30 years or more, but it is just as important now as it has always been - the buying decisions we make now will affect jobs and prosperity well into the future. Rant 1 over.

Rant 2.... I strongly suggest you only buy a boiler that has an Opentherm interface if you are to use the Honeywell Evohome system. If not you will have, as I found to my cost with a non-Opentherm boiler, frequent cycling of zone valves and boiler, exacerbating wear, making irritating noise, and using more fuel than necessary. Thankfully there are many to choose from nowadays, though many fewer if you want to buy British made.

Nest AND Evohome? One of the better features of the Evohome is the ability to display the ACTUAL hot water temperature, I don't think the Nest can do that.

As for hot water sizing, regardless of the number of bathrooms the main determinant is the number of occupants and their bathing habits....short showers? Long baths? Have you designed the three bathrooms to be close to each other so that one large cylinder may serve them all without long hot water delays? If not have you considered seperate cylinders, maybe one for the (assumed) en-suite, and a slightly larger one for the main bathroom(s).
Bear in mind also that if you have at least one teenager there is no size cylinder that they cannot empty in a single session...that's from experience!

Have you changed that roof to south facing yet? You have? Good! Now you can fit one of the many solar energy diverters available to give you free hot water (Solar iBoost, Immersun, etc) and, when the cylinder is full of hot water, divert some to the electric UFH or electric towel rails (this is easy to do at the design stage, a bit more fiddly as a retro-fit because the UFH/towel rail thermostats must be powered from the mains and their heating outputs must operate a relay to allow the diverted power to the heating elements).

Damn it, you are so lucky to be building your own house...so many opportunities, but sometimes too many choices!

MM

Thanks MM for the detailed response.

The one problem with doing a new house, as you have mentioned, is that you have to make a million decisions within the space of 5-7 months for each and every apect of the build (if you are project managing yourself) - this on top of your day job and family life. So towards the end of it when your money supply is going down fast you end up chucking away so many "nice to have" things from your bucket list. That is sadly the case here when it comes to things like solar kit on roof.

Anyways - back to the topic. Opentherm is top of my list and because of that I have narrowed down to Ideal or Atag but leaning towards Atag (not British made sadly) as they are fully Opentherm compatible and are highly rated on Trustpilot. The Atag guy came in and calculated that a 24kW boiler system boiler with a 250 ltr hot water cylinder (and an 18ltr expansion vessel) would be sufficient and that it would work really well with Evohome using an Opentherm bridge. However the difference in price between a 24kW and 32kW is roughly £100 - so again I have to make another decision on whether or not to go bigger.

Hi p_s_b,
How did you get on with your build? We are just embarking on exactly the same type of build as you and live in Putney so just down the road (kind of!).
I also want to use opentherm and Honeywell evohome, and plan to have wet UFH on the ground floor, radiators on the first floor and loft, and electric UFH in the bathrooms ensuite (sounds nearly identical to yours!).

I was thinking about going for a Heatree Sadi megaflo cylinder but also thought about with a Worcester Bosch Greenstar boiler. But from your post above I don't think will be possible as you say that you narrowed it down to Ideal or Atag - Are these the best ones you found to work with evohome and opentherm? How did you installation go? Any advice would be much appreciated!

I also understand your quote that deciding everything in a house is stressful over 5-7 months. We are a month into the build and need to decide on every single bit of plumbing and elctrics very soon in order to keep the build on time!