Search the Community

Only my second post here. Oak Frame SIP panel house now erected but a lot of construction work still to do including plumbing and heating systems. House is entirely off grid so no mains gas or electricity. We will have a large PV solar array on adjacent modern barn, with large battery storage. Thermal Store of 300 litres with inputs from Immersion ( which detailed calculations show will be sufficient for 8 months of the year), small LPG boiler and a wood burning back boiler. Outputs will be for DHW and UFH. The issue is with the wood burning back boiler which unfortunately is as far away from the TS as is possible- a full 17metres and on the same ground floor. It may be possible to move the TS to the 1st Floor, but house not desiigned for this, so weight may be an issue, in any case it would still be 17metres from the back boiler. From everything I have read back boliers are inherently dangerous due to boiling / explosion risks and reliance must not be placed on an electric circulating pump as it could breakdown. There will be an upstairs radiator / towel rail or two to act as a heat sink - but is that enough ? My suggested solution is to install a small ( maybe 100 litres) secondary HW tank upstairs very close above the log burner and have the log burner heat the water in that tank ( which would be open vented with a header tank in the loft) then pipe the water in that tank to the TS using an electric pump. That HW would in turn heat the TS via a heat exchanger (or directly). I realise that there would be some losses in the system and the pipe work from the secondary tank to the TS would need to be very highly insulated and relevant valves and stats would need to be incorporated to ensure that the secondary tank didn't inadvertantly cool the TS when the log burner not in use. Thoughts welcome? Andrew ( PS actually this is my daughters house and I'm not convinced that she and her husband or their plumber fully appreciate the dangers or complexity of their project)

Is this right? Dry sand density between 1520-1680 kg/m3 (say 1500 in the calculation below) Course sand, dry, specific heat capacity is about 800 Joules per kg per degree of temperature change. Course sand, dry, thermal conductivity 0.25 W/m K 1kWh equals 3,600,000 joules And therefore, ignoring all factoring of energy loss due to energy conversion etc(what I call "in theory"): Heating up 1kg of dry course sand would be: 450 degrees temperature change times 800 specific heat capacity times 1kg in weight, divided by the amount of joules in one kWh: 450 x 800 x 1000 / 3,600,000 = 1 kWh.

Hello, looking for a bit of advice. I’ve recently moved into a new home and the heating system is completely different to my old house (combi boiler) This house has a thermal storage tank that’s heating by a 18kw Heat only boiler and also has the multi-fuel stove connected to it to provide an additional heat source for the cylinder. Cylinder is kept at 63/64°. I’ve no problem with DHW however if I turn my underfloor heating on (15 loops, ranging in length from 110m to 54m + 3 towel rails for in the bathrooms) my Thermal store cools down to around 30° and seems to stay there, even after an hour of running the heating. I understand that when the heating has been off and the UFH is cold, I’m asking for a big volume of water in all the loops to be heated, however the UFH mixing valve is set to 45°, the water in the tank is showing 30° so my slow to heat UFH system is now even slower due to the temp of the water getting to the manifolds. As mentioned, I have an 18kw Greenstar Ri boiler and a Mcdonalds ThermFlow tank 210L - schematic below of tank and loops for the UFH. 17mm Myson pipe. Is the boiler big enough (output wise) to supply the tank hot water quick enough so I don’t drop below 45° This meaning my UFH manifolds have the correct temp water going to them to start with? Is the tank big enough in capacity to cope with the sudden request to dump the stored hot water into the floor? Combination of both? Am I asking to much of the system and just be prepared to bring each room up to temp slowly? Appreciate your help with this

Although planning a building on the East coast in the highlands, I do have a concern for over heating. Heating to be thermal store - ASHP - PV and ( possible Solar thermal)- all DIY, possibly a small wind turbine connected to DC immersion - it is windy all the time....... Anyway I got to thinking about cooling, and read some people use the ASHP and buffer tank to cool the UFH. I plan to have 6000L rainwater tank ( it also rains a bit), this tank will be underground and relatively cold, so I thought a couple of three port valves and a dedicated loop of pipe running through the tank would provide all the cooling needed and a possible heat dump for the solar. Any thoughts , problems you see.

I have recently moved to an old stone walled cottage that was converted to a bungalow in the 70s. It has a 4kWp PV system and a 1.4kWp ST system with an oil fired boiler for CH and DHW. There is a 230l cold water tank in the loft and a 140l vented hot water tank. I shall continue to use the oil fired boiler and would like to have mains pressure hot water. The ST system is a Genersys 1200 with DC12 controller which was installed in 2009 and seems to be working well. I am trying to decide whether to keep the ST system and use a ~250l twin coil TS such as a Grant DuoWave TS or use a twin coil UVC. I looked at the Harlequin Heatstream Plus but it only has one heating coil so would mean using the PV to heat the water with the immersion. I had a UVC system in my last house which worked well but it would require annual maintenance. The alternative would be to remove the ST and use an external oil fired combi boiler. I have discounted Sunamps etc. Any ideas would be helpful.

I'm renovating an 1880s Victorian semi-detached house. It's largely unmodernised, which means single-paned glass, damp cellar, damp walls, leaky chimney, vented hot water system with a cold water cistern in an overly large closet in the middle of a central first-floor room, unburied electrics etc. The upside is that it's a bit of a blank canvas and I'm looking forward to building up some self-building skills by doing a lot of the work myself. At this point I've browsed forums here and consulted with a few experts and have received some conflicting advice. I'm wondering if some experts on here with some simillar experience might be able to give my current plan a glance and poke holes as appropriate! Images incuded here are hand-drawn (I work on a screen all day, so working with pencil and paper has been therapeautic) but drawn to scale. I've tried to annotate with some indications of underlying structure and heating I have planned. It's a reasonably big 5BR house, about 2k square feet in total, and rather drafty, with as-porous-as-one-might-expect solid 9" brick outer walls. There's also a cellar underneath half the sitting room (indicated on the diagram) with some dry rot in joists and sub-floor I'll be replacing after I can get it properly waterproofed. There's also some damp coming down from chimney in the first-floor room marked library, on which I'll get brickwork repaired and walls replastered. There's a 24kw Worcester boiler feeding 7 radiators. Half the first-floor has no heating at all and seems to have been largely unoccupied for the past several decades. I'm planning to remove gas stoves from the five fireplaces, remove the current 1980s layers, restore the fireplaces to their former glory and install wood-burning stoves in several of them. I'm aware there are differing opinions about stoves, but I'm pretty set on installing at least 2-3 of these. It's worth noting that sustainability is a key concern for us, so I'm not tied to the idea of offsetting costs invested in the heating system with energy bill savings 1:1. I do want to balance outlays across the different elements of the house, so can't dump £10k into an exotic hot water system or GSHP, but getting off fossil fuel inputs as much as possible is a key concern, thus my plans to install solar thermal or an ASHP eventually alongside use of biomass in the woodstoves. My provisional plan for the (21x8') cellar is to excavate to get a flat floor (there's a good bit of rubble and the remnants of old brick flooring), put in a heavy membrane, 2" or so of sand and then a 4" wire-mesh reinforced concrete floor. I'll inject a damp-proof course into the walls, tank the whole thing, and to improve air flow put in a moisture extractor and probably also a humidifier to get moisture in there under control. I'll have zigbee / wifi humidity & temp sensors in all the rooms, so I will be able to monitor progress on this with some level of precision. I'm thinking we'll remove the radiator from the kitchen, which is the "indoor" part of an extension which has a concrete pad installed, and replace with electric UFH on top of 50mm insulation boards. Above the extension on the first floor are two rooms without heating installed. There I'm thinking I'll install a few radiators. Plan for bathroom upstairs is to completely gut and replace the bathroom upstairs, and install a thermostatic mixer shower and an electric towel heater style radiator. One key question is how to drive the heating in this overall design. On one hand, it seems like the most efficient choice would be to put in an unvented hot water cylinder (250l) and have a plumber replace the hot water plumbing to be a 22mm pressurised system. I've seen good advice on here to get extra insulation installed and it seems like I'll probably get a Telford cylinder and get an extra 50mm of insulation added to minimise thermal loss. I'm also thinking I'll get a cylinder with connections for thermal solar as I will probably add solar PV and thermal water heating when we replace the slate roof in 3-5 years. But I'm also wondering if it may be better to install a thermal store. They seem reasonable in cost, and also a bit easier to add in new inputs for heat. Ideally, I will add thermal solar and perhaps get boilers which feed in from the wood-burning stoves to store energy being generated while they are running. Hot water demand will be moderate - one bath a day for the kids and two showers for adults, which can be spaced out. There are five sinks in the house and the usual appliances. I don't need a million gallons per minute coming out of the shower, but do want to get away from the many years of combination boilers in the houses we've occupied which get cold every time someone turns on a sink. In terms of insulation overall, I've got insulation in the ground floors as a mix of insulation boards in kitchen and sheeps wool (probably in the main rooms). I'll add a bunch of mineral or sheeps wool to the roof to get that up to 330mm. And we'll replace all the windows with proper double paned. I am also wondering if, since we'll be renovating all the walls and floors and the house will be unoccupied while I do initial work, if it would be worthwhile to install internal wall insulation. This seems to be a bit expensive, and time consuming. It seems like the green home grants aren't coming any time soon to Wales either. I'm resigned to the fact that it is unwise to convert a Victorian solid wall home to a passivehaus, but also wondering if this might, conversely, be a good way to get away from that "cold drafty house feeling". If anyone on here has done internal wall insulation as part of a renovation, I'd love to hear more about how it worked for you, especially in terms of wall dampness and overall warmth improvement. Sorry for any rookie errors here - I'm still definitely learning how these systems all work together and thanks to anyone who has wisdom to share. I'm also happy to share photos of the house if that's useful.

I have my thermal store in although not heated yet. First shower is in and I am a little concerned that the pressure/flow is low and it drops noticeably when you are looking for hot water (even though it isn't hot yet). Water is a balanced supply through a thermal store for hot and balanced off a multibloc pressure reducing and relief valve for the cold. Pressure at mains outside is 4-6 bar and flow somewhere around 40l/min. Can't keep the water in the bucket when running full bore at the start Haven't had a chance to chat with plumber yet as it is the holidays in NI but feels like the water system is strangled when it is within the house. Anyone got any pointers for me.

I have posted previously about some design questions here I have settled on a thermal store with 2 ufh manifolds and a radiator circuit. Looking some direction on my thoughts of how to connect this all to thermal store. - Boiler connected via 2 port valve controlled by tank stats. 2 tank stats controlled via time clock one for summer (no ufh demand) one for winter. - UFH zones and rads off a single tapping from thermal store, or should I separate rads to their own tapping? Either way each will have a 2 port valve. - UFH pumps connected via the switched live from the zone valves, think I seen @Nickfromwales recommend this previously. - Rads will be controlled from time clock and 2 port valve triggering their own pump. Is this correct? Should I do it different, I don't mean ashp instead of boiler? Have I missed anything? As always thanks in advance.

Needing to focus on my next project after my UFH fiasco and being in a holiday rental place where the DHW is very hit and miss reminds me that I need to get some specs laid down before I start ordering stuff! Having read so much over the past couple of years, I feel a lot more informed but also a bit bamboozled at the same time. UVC or TS, buffer tanks, what size..... So my main questions (so far): 1) what type of gas boiler to go for? 2) Thermal store or UVC? 3) Buffer tank needed? My setup will be: 4kw solar PV Mains gas 2 UFH manifolds (upstairs and groundfloor - so I can choose the flow temps accordingly to get the maximum comfort levels) Room stats in all areas 2 Bathrooms (2 showers, 2 baths) MHVR Although not going to be a passivhaus, I’m hopeful it'll be a bloody whole let better than your standard newbuild: 2 SIP extensions 300mm EPS floor insulation 3G windows/doors 100mm EWI on existing house DHW requirement: 2 adults and two soon to be teenagers (so they will hardly wash reducing the DHW figures a bit) 2 morning showers 2 evening baths Hot water for washing up (though may get a boiler-type tap for most hot water needs in the kitchen) Occupancy: Wife and kids out and I although I work from home, my office will be one of the sheds out the back so main house can either be set to off or very low temps during the day. UFH demands: Groundfloor: Water volume: 129L; Estimated loading: 9.45Kw Upstairs: Water volume: 25L; Estimated loading: 2.03Kw BOILER QUESTION: Before I start getting plumbers out to fit a boiler system, I’d like to get people’s advice on whether to go for system or combi. Combi = don’t need a water storage cylinder = no need for cistern in loft = combi boilers don’t supply enough hot water = better to use a separate cylinder for the hot water supply. = combi boilers can be quite noisy. System = Store hot water in a cylinder, so they can feed several outlets at once at mains pressure. = no need for a cistern in the loft and the expansion vessel is built in. = Flow rates will be high as water is delivered at mains pressure, and hot water is instantaneous. I'm thinking to go for a system boiler at this stage (easier/quicker install) and then to use excess PV with the cylinder. THERMAL STORE OR UVC? My thoughts so far are to have a 300L UVC fed partly by the solar PV during the day (using an Immersun type of device) with maybe E10/E7 at night and then also the gas boiler. I would end up with two circuits – one for DHW and one for UFH. The boiler would kick in for the UFH when the UVC doesn’t require heat. BUFFER TANK? I'm also thinking that if I go for a UVC rather than thermal store (from what I have read on here) I would need a buffer store seeing I will have UFH. But I've read that if I opt for a TS, that can be my buffer tank also. So perhaps I should go for a TS rather than a UVC? Confused.... Hoping someone (AKA: @Nickfromwales etc) is able to assist..... Thanks, OB

@Nickfromwales Telford seem a good bet for supplying my UVC. As per other post on UFH with rads but I will now site the tank in the cellar and have an external boiler (fluing from the cellar is a pig and looks expensive). So presume new system boiler and UVC or TS. Can't invest in solar now, or air-source hp as no funds left. See system below I got quoted from Greensquare. Should I not have a buffer if going uvc?

Into detail design stage for an extension to existing stone cottage. Basically a timber clad 2 storey box with a glass link to replace single storey hotchpotch that is there now. MBC have quoted for a passive slab (ouch£!) but due to size restiction will go for u=0.14 walls (open panel , 300mm finished) and u=0.14 flat roof by MBC if I can deal with the + VAT price. Existing gravity DHW gravity fed with pump for shower, supplied by a 2009 year oil fired Grant 15/28 kw utility condensing system boiler that also runs the rads. The rads will have to stay in the cottage but how to run UFH in the extension.. Based on an MBC house build nearby I'm pretty sure I won't need any heating on 1st floor apart from electric towel rads and/or electric mat for en-suite (although they don't have a link to a drafty cottage so slight concern!) Yes I'd like to do away with the oil boiler but not sure I can considering the poor performing cottage and potential costs. I'd like to go mains pressure also so UVC, (mains flow rates of 40 L/m). If so then potential for solar PV or solar Thermal if worth the investment. Do I fit a buffer for UFH to stop short cycling? Any thoughts? Any alternative schemes?

So we are going to install a 500l thermal store into the utility room. This will create quite a bit of heat I suspect and it would be good to spread this round the building. In fact next to the utility is the integral garage which is full insulated - 60mm internal insulted PB, triple glazing and an insulated garage door. Would it be mad to put a single room mvhr system between these rooms to gentle heat the garage with the excess heat from the the TS?

Looking at ordering one of these up shortly. House is UFH all the way through. 1970's build with 60mm internal insulation all over, triple glazing and loft and slab insulation. So it's insulated to a modest standard nothing more. This ain't no passivehause! Build has 8 zones of heating and circa 2800sqft of living space with a couple of 5kw wood burners. Plan is to use the existing condensing 37kw oil boiler as a primary heat source, later down the line we'll look at some micro hydro from the millstream as a backstop (thinking circa 2k continuous) we can then augment with an ASHP or similar if we want / need to. Any thoughts?

Hi everyone, I'm a "mature" retired electronic/electrical design engineer come computer networking consultant come PH self builder. See following link for existing building details. http://passivhausprojekte.de/#k_4186 Currently designing second PH for construction in Brinkworth, on Woodbridge park golf course. Build commences 2nd August. Also designing next door neighbours from PHPP perspective. Scandanavian Lodge design ( planning requirement), Isoquick insulated raft foundation, Beco ICF walls (polstyrene lego bricks according to my wife!), attic trussed warm roof. Approx. 240m2 and 550m3 gross including voids which are within thermal and airtight envelope. Techie bit. Hmm.. The intension was to have very similar to current house as it works well! However no mains gas so all electric. MVHR to be a Paul Novus 300 with Lindab rigid safe ducting, silencers etc. Thermal store to be Akva Nero 750l (current house has Akvaterm std tank of 500l with top and bottom DHW coils giving up to 35l per min). Change of size result of no mains gas and probable use of Eco7 electric to supplement Solar PV via Immersun PWM switch to two high temp immersions. Space heating via VEAB CCW 125-6-2.5 in living area duct branch only - no active heating to bedrooms. Summer active cooling via VEAB CWK 125-6-2.5 in bedroom ducting only or VEAB CWK 160-6-2.5 for all areas... 3kW ASHP air to water supplying the VEAB CWK. Secondary DHW loop to provide "instant" hot water to all areas with little potted water wastage (as per current house). Well that was the plan until I discovered Sunamp and Zehnder Comfocool Q600! So undecided now although no apparent pricing/availability of Sunamp Stack.... Sunamp PV 5kW units look good but only a fraction of the capacity of a 750l TS. Multiple units look very expensive by comparison. However, need to make a decision soon I guess.......

Whilst I deliberate over the tank design: In my 1 tank design I have included a 4 port mixer from the TS : The Lower part of the TS being around 40oC the top being 60-80oC (load dependant), however my UFH only requires around 23oC, so the plan was to take it out of the store at around 30oC and let the manifolds do the rest. However a 4-port valve with actuator will mix some from the top some from the middle and some from the bottom (I think) to achieve the desired output utilising a valve like this: This means that I am utilising high grade (expensive) heat when I don’t need to. Would it be better to use 2 x 3-port mixers as follows: The first mixer isolating the top (hot) part of the tank unless there is a drop in the lower part that needs boosting, then the second mixer doing the final blend with the bottom/return leg. Would this be more efficient? Also I could use thermos actuators (no electricity). Potentially I could do away with the TMV’s on the manifolds if I put the second mixer to the desired temperature, but that is for another day. Thoughts please.

I am moving towards finalising the design of the Heating/Cooling and DHW system. The house will have UFH/cooling supplied from an inverter ASHP that can also cool the floor (and supply cool water to an MVHR duct cooler), heat load of 3.4kW over 419m2 from PHPP. However we have a high DHW requirement (after long discussion on the previous forum) I have got it down to 27 L/m at ∆T of 44K with a usable capacity of ≈400L. (5½ bath house). I was looking at having a separate buffer tank for the UFH (200-300L) which could also pre-heat the DHW (a la Jeremy's layout, just bigger) followed by a Thermal store (300 – 500L) to supply the DHW (We have Mains Gas so boiler power). This would separate the 2 systems (recommended by most on the forums) and allow me to run the TS at variable temperatures (50oC – 80oC) depending on required loading (low occupancy – high occupancy), whilst eliminating the Legionella problem with a UVC at low occupancy. I would also cross connect the heat generators so the ASHP can provide low grade heat to the lower part of the TS and the boiler can supply the Buffer during ASHP high load/failure. However I am now considering just one larger Stratified TS (750 – 1000L) to cover the whole system. This would make plumbing and specification easier and theoretically the thermal losses from one large tank should be less than 2 smaller tank. eg. AKVATERM AKVA GEO 300 64W AKVATERM AKVA GEO 500 75W AKVATERM AKVA GEO 750 89W AKVATERM AKVA GEO 1000 96W So the 300 + 500 gives me 139W (although the 300 would be at a lower temp so less loss). Yes I know losses will be higher but as a guideline. I have been looking at the Sunamp Stack but it is only available as a complete stack 40kWh and would not support the low temperature of the ASHP (requires high temp to charge > 58oC). What would the collective experience go for with regards separate tanks and giving individual (if cross connected) systems vs one all singing (overall lower loss) tank?

Excerpt from a previous thread. A member asked..... I am looking at an HTG thermal store for a DHW & Heating upgrade, I will be using a gas boiler heating the TS only, together with PV and immersion heater. The TS comes with a solar thermal coil fitted as standard. The gas boiler would normally be connected directly to the TS but I was wondering if I could use this solar coil for the system boiler to obtain some fluid separation ? The size of our home with # of radiators/bathrooms etc. would suggest I need a TS of around 300 litres but if I view the store as a battery should I install a larger store say 400 / 500 ltrs to help with the gaps in PV availability ? I guess there is a risk of oversizing as the volume should be within the capabilities of the immersion / gas boiler to recharge it ~ any thoughts or advice would be welcome. The TS is presently required for 12 radiators, 2 bathrooms & DHW, I am hoping to take advantage of my PV power hence the TS otherwise a fair size combo probably would have been the way to go. I am also building extra ground floor space so I also have been considering UFH but from your previous advice I am going to need more insulation to even consider going down this road. I have a beam & block floor with only 40mm poly then wyroc so not good, I am able to put 75mm underneath the floor between the beams which would help ~ but still not sufficient although if I am using this space underneath the ground floor as a store should I be too concerned. I have had experience with TS excessive heat in a flat some years ago, it was located in the centre of the flat off the hallway and I did ask engineers how to reduce the heat output but they looked blank at me. The small gas boiler was set at max heat output for efficiency as per the operating instructions but after not getting any useful help from heating guys, I had to turn the boiler down to half heat which totally made our lives much better, so JSH I appreciate this problem..... I presently have a traditional copper tank upstairs about 110 ltrs and is generally heated by the PV system and overall meets our requirements as there is only two of us. I am considering putting the TS in the utility room and using the heat to make a drying room etc. The TS is stainless steel and comes pre plumbed with a high efficient external heat exchanger (46lts per min, we have high water pressure) I could also add to this TS a similar external heat exchanger for UFH so it would give me scope for going the UFH direction. The additional copper header tank can be installed above the TS , is there any requirement for this to be higher than the radiators in the bedrooms or will it be ok ?