Optimum evohome installation

[AlWilliams]

In a few weeks, we're ripping out our one pipe 1960's system and installing a totally new setup. Current broad specification is a system boiler, 210 U/V Cylinder and 10 rads. We're in a 4 bed detached with two bathrooms.

Given it's a blank canvas and we use our home very differently through the day and day to day, I'd like to fit Evohome so I can zone the rooms and only heat what we need, when we need it.

Our plumber is happy to fit what we want, leaving the binding of TRV's and set up / scheduling to me. He's currently suggesting a circa 30kw Baxi or WB boiler. Though, he's not used evohome before so he's relying on me to make sure everything evohome needs is covered.

One question I have is concerning opentherm, is it worth it? Using this to allow the boiler to modulate the flow temp to maximise efficiency? From the looks of things, it's not well supported from the boiler side and what would we lose or gain from alternatives?

Apart from that, is it as simple as just installing everything then setting evohome up or do we need to consider other elements / components when building the system? I just want to be certain we're considering everything we need to and don't end up with something that works poorly.

 

[muggles]

I think you need to start by finding a different installer to be honest. If he's suggesting 30kW for 10 rads, and Worcester or Baxi as your best options (neither of which are OpenTherm compatible, or particularly good boilers) I fear he's not going to give you the system you're looking for.

OpenTherm is very good when implemented well - it's a control language with 128 data sets, and some thermostats and boilers understand more than others. You've started well by choosing the best OpenTherm controller going, but this needs to be paired to a boiler that implements the OT protocol well in order to maximise your gains. The best OpenTherm boiler I've seen in action (spending time watching an OpenTherm monitor to see how the boiler and controller talk to each other) is Intergas, which also happens to be one of the very best boilers on the market.

A condensing boiler (any condensing boiler) will only condense when the return temperature is below 52°C. Any higher than that and it becomes a standard efficiency boiler, using more gas than it needs to. Size your radiators based on 70/50 or better still 65/45 flow & return temperatures for best efficiency. Use Honeywell or IMI Eclipse valve bodies. I prefer IMI as they're easier to balance, helping with even heat-up of your home, but they're not so easy to come by (I have a direct trade account with them).

If it was me, I'd be looking at an Intergas ECO RF 24 connected via a hot water priority setup to a Joule Cyclone cylinder. Hot water priority with Intergas gives you really fast reheat times on your cylinder, and the advanced level OpenTherm gives you maximum efficiency on your heating.

Hope that helps!

 

[AlWilliams]

It does, appreciate your advice.

We're a little stuck in terms of installer, I spoke to many before the one we chose and they simply didn't want the job, couldn't till next year or wanted £10k. Though the current chap comes very well recommended locally.

It's a complex arrangement, specifying a whole new installation, including smart controls and I'm trying to get to grips with it as best I can. At the least I want to make sure what we're aiming for is sensible and achievable. I've been recommended OT, I don't fully understand the alternatives so I'm keeping my mind open, but understand the controls on efficiency it offers, which are attractive to us.

Rads have already been sized for delta T40, so we should be good for running in condensing mode.

I'll ask about the boiler again, he's recommended what's familiar to him, but is open to different options if we specify. Regarding intergas, a quick google is telling me the ECO RF's are combi's, would the HRE SB's be similarly compatible? I had looked at Viessman before as I believe they're OT compatible too, so I'll revisit my earlier notes. I had my suspicions that 30kw may be generous, but as extension work next year will add another four rads and 40+ sqm, I'm not too bothered.

 

[muggles]

If your profile page is correct and you're in Oxfordshire, then £10k-ish is probably not unreasonable, although obviously I've not seen the job so I may be wrong (I'm also in Oxfordshire, so familiar with local pricing, and labour costs are high because living costs are high as I'm sure you know). There is an element of getting what you pay for here though, and squeezing a bit more out of the budget can give you better results in terms of running costs, although specification is key of course. Good to see that some consideration has been given to radiator sizing though, that's a start.

The ECO RF is indeed a combi, until you change a parameter in the settings, at which point it becomes a system boiler with a 10-year warranty. Intergas are perfectly happy for this to be done, and an ECO RF is almost the same price as an HRE SB, so you get 3 extra years' warranty for very little additional outlay, which is why I specify the ECO RF for my customers. There are a host of other parameters which can be configured on the Intergas to set the boiler up for the system it is attached to and ensure best efficiency as well, which is another reason I like them - they are almost infinitely configurable, so that when correctly set up they outperform pretty much anything else out there.