Ann D Mann

Re JohnMo's link to the ATAG literature I'm beginning to wonder if our mixture of UFH and rads will mean we wont be able to enjoy the sophistication of the ATAG In regard to gradient speed settings We'll have two types of heating system that appear to require different setings: 1 – 2 underfloor heating 4 – 5 Radiator convectors Do I select setting 3? and just to throw a real spanner in ... We had planned to distribute to rads via individual circuits from a UFH manifold, Each room to have a stat controlling the corresponding actuator. The ATAG manual suggests TRVs and one ATAG controller In case it affects opinions .. we also have MVHR

So.. choose boiler that can modulate down to as low as possible and is sized to meet the house heating demand plus HW requirements Ok Proposed boiler (ATAG) is >30kW. Turn down ratio 1:10 min modukated op =3kw? My floors require 6kW each Not sure what to allow for dhw. But it looks to me like 30jW boiler is not too much Or am I still uneducated?

Hey Marshian Thanks for linking this video. Very clear presentation. Learned a lot I was still very much in the dark ages and unaware that condensing boilers function best with Delta T at 20C The blogger's advice suggested we’re all buying boilers about 2x bigger than necessary I'm being lazy now cos my next post is not really thread related. If the question's been covered elsewhere, - any pointers welcome. I had a closer look at our heat losses (at -2C) GF calculated by UFH supplier (OMNIE) = 6.5kW 1 F calc'd by me and hubby = 6kW (it'll be rads ) Not sure what to allow for DHW especially if we go PDHW ATAG Boiler proposed. ATAG claim a turndown ratio of 10:1 We have Family bathroom with shower and a 2nd proper bathroom, WC , Kitchen & Utility We think 250Ltr tank required..? How do we decide what size boiler to get? Blogger also talked about load sensing thermostats and the inconsistencies between them and boiler systems Our intention was to buy stats from OMNIE But now I'm concerned about compatibility with ATAG Duh!

On WC the flow temp is almost rock solid, on thermostat operation it will keep adding to flow temp approx 10 mins after starting and will go up to max temperature set in the controller JohnMo Re, ATAG... Does this work alongside PDHW that was discussed in thread. None of the plumbers that I've spoken to have mentioned any if this so I'm trying to get a handle on the questions I should be asking

Dear members We hoped to get frank responses and they have been very thought provoking. Thank you all. We haven't ruled anything in or out yet, but before you launch another tirade of why we shouldn't install this system.. In the OP I said "if this seems mad to you, I have to admit it's an experiment and probably quite costly" We're still hoping to get advice on the three questions posed in the OP if anyone wants to have a go..? The PDHW proposal is not something we'd previously discussed. Our preferred Boiler (ATAG) supports the tech so we can explore it. From what was said, the benefit seems to be in the flow/return DeltaT and condensing process. Is that right? Is this a more compelling or contrary reason for us to install the buffer? If I understood correctly, its better to keep the condensing boiler return as close to the temp of the flow, If that's so and water in our buffer is warmer that the boiler return then referring to the schematic: V3 swings to V4 and the return to boiler is via the warmer buffer. Thanks ADM

Er..um this sounds very similar to our plan A (see OP). Sadly we cant fit a big enough TS in the ideal position... .AND because the wood stove flow temp is always likely to be lower than gas boiler, there was a strong chance heat would be lost from the TS to the LB

The safety of our proposal has been our priority. We posted a schematic with the OP There's a heat leak rad that could always be deployed ... but in case of power failure the N/c valve would ensure all Stove heat was diverted to this rad Also.. The o/p from our back boiler is guestimated at 1.5kW . Is it likely to kettle given that we're proposing a >100ltr buffer?

Remember that temperature is not energy. If i could stress the content of the OP. The Stove is decorative. We never intended it to be a primary heat source. We are "waste not want not " people and it seemed silly NOT to try and capture some heat with a back boiler.

Is this different to what modulating boilers do?

I'd be interested to hear more We don't anticipate using the WBS in summer and the gas boiler could feed the dhmc via the s plan system without heating the buffer Correct but then all the rads and ufh are also not used in summer either Don't think you read the op. We only think of the WBS as contributing

Sorry to be dumb. Could you expand on this? It seems like I coujd be wasting a lot of energy. (Mine not fossil)

Looking at posts here there are some very experienced & knowledgable people around and I hope you'll be generous enough to help me out. If you want to avoid the back story skip to PLAN C We have major refurb in progress. An 8kW Hamlet log burner came with the house plus several 10 x m3 of seasoned logs We'd like to use the stove and thought it would be clever to harness any surplus heat by retrofitting a back boiler and hooking it up to the new Gas CH System. Arrada sold us a back boiler unit bespoke for the Hamlet stove but it's quite small. It seemed clear that the back boiler would never be able to compete with our gas boiler. Plan A was to use a >250 ltr thermal store with the gas boiler doing the heavy lifting and a stove coil at very low level (just to contribute without stealing any heat) DHW would come from a heat exchanger either in or alongside the TS. Sadly the ideal 1st floor location is too cramped . We underestimated the insulation ! Plan B was to install a smallish (100 / 140 ltr) buffer in the place originally intended for T.Store, - almost above the log stove The stove and gas boiler would both contribute to the buffer which would also be connected to a typical S Plan for CH & a separate "normal " DHW Cylinder The separate DHW cylider came about due to the shape of the house and position of most used rooms. The fear about Plan B was that the Log stove flow would likely be several deg lower than gas boiler flow and the log burner would steal heat from the system . So Plan C (schematic attached) is to (i) use the gas boiler in normal S plan configuration and (ii) isolate any heat generated by the wood stove in the buffer (iii) Allow heat from the buffer into the system if it was warm enough and can contribute (iv) use differential temperature sensors to control the valves (v) incorporate a load unit (probably "armatur" ) to pump water through the back boiler till it's warmed up . The load unit should permit gravity only when the temp is high enough (50C we think) (vi) provide for unlikely situation where buffer water temp can support the S Plan system (dotted line of schematic) Heat o/p of back boiler Given the Arrada back boiler/ heat exchanger only holds 3ltrs of water we think it's unlikely to provide more than 1.5kW - if that were most likely to have fires during winter months and probably mostly late afternoon / early eves. So burn times about 6-8 hour session If so, we think it will take most of a session to lift 100 ltrs of water in the buffer from 12C (nominal) to a useful 70+C what we're expecting to happen Any water warmed by the wood stove in an evening will stay in the buffer overnight.. Then when the gas boiler fires up in the morning the warm water in the buffer will provide prewarmed water to the boiler return saving a few units of gas I should stress that if this seems mad to you, I have to admit it's an experiment and probably quite costly. BUT if the scheme is successful we could improve our fortunes with a bigger log stove in a few years time. IT could do more work. Questions 22 or 28mm? We believe we should stick with 28mm throughout the wood burner gravity system It's been suggested that we could drop to 22mm on the buffer coil. What would you do? Which tank ? Vented / Unvented Telford & Gledhill both make "gravity tanks" with 28mm tails to the coil. But they're listed as vented It always seems to me that unvented cylinders hold heat better than vented and I'd like to not vent our buffer Could expansion via a PRV/Tun dish work? If there was a loss of water via the tun, I'd have to let more cold in via the filling loop. I haven't got a solution to this What would you do? F&E Tank If I had to vent the buffer, could I use the same F&E tank earmarked for the log burner? What would you do? The Scheme Your thoughts comments and criticisms will be most appreciated