Barnacles

Yeah, I have a local sparky who I've worked with in the past. He's happy for me to do the work and he'll inspect it and sign off if he's happy. I just don't like to pester him as I appreciate that he's a busy bloke. I'd rather go to him with a plan of what I intend to do and know that I'm on the right track than ask him to spec the whole job for me. There's no info at all on the specs regarding the startup current. We had an ASHP 10+ years ago (at our old place) that was non-inverter and pulled about 6kw when running. I dread to think what the startup current was on that but the neighbours did wonder why their lights kept dimming and certain times of the day! We swapped it out for a gas boiler and never looked back. ASHPs have come on a bit since then I believe. Reading about compressors and their startup currents they usually quote a SLA (Starting Load Amps) of around 2-5x the normal running current and RLA (rotor locked amps) at nearer to 10x. But, I gather that if it's drawing anywhere near it's RLA it is probably not much longer for this world. It's actually a wood-fired hot tub with a small in-line electric heater. I'm doing away with the stove (fine in the summer, a right pain in the winter!) and probably the heater too so I'll just have two 50mm pipes sticking out of the side that I can connect the pump/filter/ASHP to. Should be pretty straightforward - famous last words! If I was starting from scratch I would do just that but I already have a 1.5mm2 SWA to the tub for the lights and the small existing heater. It's not a huge job to replace it I suppose but I'd prefer not to if I can get away with it 😀.

Hi All, We have a small hot tub and I've decided to add a ASHP to reduce running costs. The unit that I've bought is rated at up to 8kW heat output and the electrical draw is rated at 1.32kW. It isn't an inverter model so there will be a bit of a thump when the compressor fires up. The cable run is about 10m. I've read a lot about it but I can't find a definitive answer; do I need to go larger than 1.5mm2 SWA to supply the ASHP? Obviously the start up current will be fairly substantial but will it be more than the 1.5mm cable (rated at 27A when clipped and in free air) can safely handle? I'm leaning towards using a 10A D-curve mcb, would that be sensible? The only specifications supplied in the manual are: Input Power 1.32 kW Power Supply 220-240V / 50Hz Current Rating 5.9 AMP Thanks, Paul.

The house is a 3 bedroom cottage that has recently been completely renovated. There is a MVHR system and the whole place was extensively re-insulated and underfloor heating installed. I'd say it still isn't super air-tight but for an old house I'd say it should perform reasonably well. I have no idea what the actual energy consumption was in terms of kWh but I could ask and find out, she did say that her electricity price was fairly standard so I'd assume around 30p per kWh. That makes sense. So if she installed a small stove in one room and used it for 3 or 4 months of the year, in theory her RHI shouldn't be affected too much and as long as she declares it on her annual declaration she should be all good.

Thanks for the replies everyone. It didn't make sense to me that she shouldn't be allowed to have a stove or PV installed. I'm going to nip over tomorrow and give her the good news, she'll be delighted. I'll mention the solar thermal too, I've a feeling that she may have a spare coil on her cylinder to accommodate it. I think the person who set up the ASHP should be flogged! Last winter she was paying over £1500 per month to run her ASHP and it's not even a large house. I went and had a look at it and found that it was set to output water at 23 deg C so it had been running virtually the whole day without actually heating the house. The DHW was set to come on for 30 minutes at midnight so it had been using the immersion to heat the water instead. The room thermostats were all set badly too so we configured all of those. She's now paying more like £300 per month but that still sounds very high to me. I think she needs to get an expert to set the system up properly.

Hello all, I was just chatting to my neighbour and we got on to the subject of her ASHP. She's had it operational for about 2 or 3 years and qualified for RHI for which she is receiving her payout from Rishi & Co. We'd been talking about firewood and I asked if she needed any, she said that she wasn't allowed to have a wood-burning stove (or any alternative source of heating!) under the conditions of the RHI agreement. Does that sound right? She mentioned how much she was spending on electricity each month to run the ASHP and I almost passed out! I suggested that she should consider PV panels to help power the ASHP and again she said that under the RHI agreement she couldn't install a PV system. This seems utterly illogical to me, is my neighbour misinformed? Thank you, Paul.

Hi All, We are building an extension to our kitchen and as part of the works we are looking to relocate the CU, electric meter, incoming supply fuse etc. I would like to install a new recessed meter box into the wall of our boiler room (it's an oil fired boiler) which is constucted of a single skin of 4" solid blocks. The CU has a new location in the house but everything else will be in the new meter box (including a KMF switch as CU will be some distance away from the meter). Our DNO have said that we can locate the new meter box anywhere on the gable end of our house that suits our works. Firstly is it acceptable to install a recessed box into a 4" wall as the back of the box will be stuck right though the wall? Secondly, is there any problem with being relatively close to the boiler. I've searched the web and can't find any reference to oil boiler and/or flue distance to meter box. Is there a regulation for it? The meter box would be approximately 300mm horizontally away from the flue and there would be about 150mm between the back of the meter box and the case of the boiler. Any advice would be much appreciated.

Thanks All. At this point I'm seriously considering doing it myself but I'll sleep on it a while longer and see how the hunt for a builder goes.

Thanks Nod. I know exactly what you mean, we do tend to operate on a "just-in-time" basis 😆 Block and block certainly sounds quick and cost-effective. After a very amiable meeting with the builder for almost two hours on Friday afternoon about the project, and after a fairly sleepless night thinking about the project, he called my wife (he couldn't even call me!) on Saturday to say that he wasn't going to be doing the job... AT ALL!! Without any reasonable explanation he just decided he wasn't doing the work. I was floored! We had nothing in writing because in the 15 years or so that he's been doing work for us we've never needed it, he's always been as good as his word. So now it loks like we're back to square one again, choosing a new builder and then waiting in line for goodness knows how long. Come Tuesday I'll be on the phone in the quest for another builder.

Hi All, Our builder called round yesterday to say he'd had a cancellation and could start our small, single-storey extension next week (about 6-8 weeks sooner than we had planned) if we wanted him to do so. Given how difficult it is to get a decent builder to even quote for a job at the moment I rather hastily said it would be fine. Now, as I realise how unprepared I am I'm starting to worry a little. I like to be fully prepared for something like this and that includes understanding the methods and materials that they'll be using. It will be at least a week after they start until they actually start building (there's an existing structure to remove, drains to lay, water main to re-route and foundations to dig and pour) so I have a little breathing room. The extension will be 3.2m x 1.6m and sit in the L of two existing solid stone walls (one of which is rendered) so we're effectively building just the two new walls. We are knocking the exisitng outer wall through to make a larger kitchen, that wall is 400mm thick stone. I asked about what type of structure they would use when knocking through and they said proabably Catnic lintels supported in the wall on one side and on vertical steel posts at the other. Having looked at Catnic lintels I'm not sure whether they are the best choice for stone walls? I'd also be grateful for your opinions on construction methods for the walls. The builder proposed three different methods: double skin wall of concrete blocks with insulation between, single skin block with timber frame inside and insulation in the framing, timber framed with either timber cladding or a stone veneer. I imagine that each method has it benefits and drawbacks but as of today which do you think would offer the best combination of thermal efficiency, acoustic insulation and value for money (based on both material and labour costs). Is there an alternative construction method that I should be aware of that isn't overly complex, expensive and suits the scale of this project? As far as looks are concerned there is exposed stone to one side of the extension and rendered stone to the other so either stone or render will be cohesive, I suspect that timber may look slightly at odds being a third material type. I feel like my back is to the wall somewhat but I don't want to pass up the opportunity to have the work done if it means I have to wait another 6 months to get them back again. My builder and agreed to take the weekend to consider the project and discuss it again on Tuesday. By then I'd like to have a clear idea of my best options so I don't get strong-armed into something I'm not entirely happy with. As ever, all thoughts, contributions and opinions are greatly valued.

👍That's what I wanted to hear, thank you. We needed an indemnity when we last sold a place and it was only £100 or so so if we had to do it again it's no drama. There aren't any side windows in the extension and we don't have any neighbours on that side of the house so hopefully that won't apply in this case. 🤞 Thanks for the advice, I'll get on and start drawing up the plans. Our builder is very "old school" and would gladly build it from a cigarette packet sketch but I suspect Building Control will want to see more than that 😁

No, not really and the house isn't overlooked (well the nearest house on that side is 200m away). The part about staying put for a number of years might be the fly in the ointment. 🙄

Hi All, We're considering replacing an existing single storey lean-to extension with new structure, essentially on the same footprint. We're in a detatched house with plenty of space around. I've read the PD documentation and couldn't find anything specifically relating to this situation. The current extension consists of a brick built wall about 1m high with conservatory style glazing above and a glass roof which constitutes a porch area. We would like to replace the structure with something more substantial and better insulated then knock through to create a larger kitchen. Construction would probably be rendered block to harmonise with the section of building it will adjoin. A new casement window will be fitted to the front elevation (significantly smaller than the existing glazed area) and one or two roof windows would be fitted). Do you think we need PP or will PD cover it? Or would neither apply if it were considered to be just an improvement of the existing structure?

Yeah, I was worried about that. There are some air air vents but they are small. The bathroom currently has an extractor fan in the ceiling which is ducted through the loft to an outlet. Once the system is running and the bathroom extractor fan is rendered obsolete I think I'll leave that outlet open to allow more air into the roof space. The outlet is at the opposite end of the building to the MVHR unit so it should pull air right through the loft. If it's not sufficient I'll stick in a few strategically placed soffit vents and see how that goes. The building envelope does appear to be reasonably well sealed but I'll be running around with the silicone or expanding foam where there are pipes and cables that puncture the envelope. I'll keep you updated.

Just a quick update. I bought a Nuaire MRXBOX unit which arrived earlier this week and I've spent most of the week cramped up in a cold loft doing the installation. I'm almost there, I just have the condensate drain to connect up next week. The Nuaire unit is very compact and neat and looks to be well made. I can't wait to get it fired up and see what a difference it makes. Just as a side note, having read a few opinions on the subject I decided (controversially) to try drawing the supply air from within the loft through a filter box. It's the first time I've been in the loft since buying the place and there's a lot of mould on the underside of the membrane so I believe there's not enough ventilation in the roof space. My thinking is that by drawing the air from the loft it will pull fresh air in to the loft and better ventilate it. I realise that in summer the air in the loft will be very warm and my solution is just to turn the MVHR unit off in summer as most guests have doors and windows open most of the time anyway. I'll be keeping an eye on it and if I notice any adverse side effects I can easily drill another hole in the outside wall and run another duct. As ever, I'm grateful for all the knowledge, wisdom and help offered here ??

I haven't come across those, I'll have a look. Thanks. In my bedroom the vent is about 0.5m to the side of the bed head and I only notice it on very cold nights. However, I'm installing a system in our holiday cottage, which is generally a slightly colder building, and don't want to "blast freeze" our guests ?. I was thinking I would lke to direct the flow mostly towards the wall where we have the most condensation and away from the head of the bed, does that make sense or is it better to just have an overall general ventilation around the room? That's a thought. I did commission our home system about 3 years ago and it was set up as per the best available information regarding flow rates etc but it might be time to check it again and just see if it's still in balance as I have made one or two tweaks recently.

Hi All, Does anyone know where I can buy directional diffusers? I'm fitting an outlet in a bedroom and don't want the occupants to be laying in a draught. I found a link here on Buildhub to CVC Direct who sell one: https://cvcdirect.myshopify.com/collections/ceiling-valves/products/turn-airvalve-125mm But when I try and buy it I'm told that they're not accepting orders at the moment. I'll try and contact them tomorrow but does anyone know of another supplier. I've tried BPC, i-Sells, Blauberg etc but no joy. Has anyone tried modifying standard diffusers to be directional? I guess a good squirt of silicone would block up part of the outlet but would render the diffuser's flow rate unadjustable. Thanks, Paul.

Apologies for being late to the party on this one. I have the same Titon unit in our house and had the same problem with the gurgling sound the first time it got really cold after installing it. I don't think it will be such a big problem for you as you have a fair drop of pipework for the condensate water to escape under gravity. I have a shallow fall on my pipework and hadn't properly sealed the condensate outlet pipework. In my case the extract fan managed to suck water up into the fan and destroyed it. At £220 for a new one I was kicking myself pretty hard about that one. Some duct tape around the tundish will probably suffice for now but longer term I would certainly seal the pipework completely.

I've spent the day looking at various options and concluded that MVHR is the way to go. The layout doesn't really lend itself to PIV, I did almost plump for a dMVHR (as much to make my life easier on the install as anything!) but then in the end I figured I that MVHR is the "belt and braces" approach which will hopefully tick all the right boxes. I have quite a few bits and piece left over from previous MVHR and A/C installs so I can save money on the overall spend and I found a Nuaire unit for £699. Along with the other bits I need to buy I should be able to bring it in under £850 or so and I'm happy to fit it myself as it's relatively easy to work in the loft space. It's still more than I wanted to spend initially but if it cuts down on the maintenance and keeps the place fresh it's got to be a winner. Many thanks for all the suggestions and advice they're very much appreciated.

Hmmm, that's a different way to come at it, interesting. There is a bog-standard humidity controlled extractor fan in the bathroom already but with all the cold surfaces in there it's just doesn't cut it, we still end up with pools of water on the window sills (also stone!!). Insulating the walls would likely be impractical due to the amount of space we'd lose. My only concern with a dehumidifier would be the noise. I haven't used one for about 20 years but the one we had was really noisy, have they got any quieter in recent years? You're spot-on Mike2016, people don't open windows etc. What ever solution I go for has to be fully automated and tamper proof. One thing is for sure, if there's something for guests to tamper with, they will tamper with it ?

Hi all, i am looking for a small MVHR system for our holiday rental property. We have a lot of condensation and mould problems in the en-suite bathroom and the bedroom suffers slightly from the same. I am looking for a system that will cover the bedroom and en-suite and possibly the living area too (thought there’s no damp/mould etc in there). Unfortunately there’s no way I can incorporate the kitchen in the design, there’s just no way to get a duct to it. The bathroom is small (about 7sq. m) and has mostly solid stone rendered walls. The bedroom is about 22 sq. m and has one stone wall. The living area is 28 sq.m. There is a small cold loft space above the bedroom which is likely where the unit will live, thought f the unit were sufficiently small it could live in the airing cupboard off the bathroom. I had thought that I might use a Vent Axia HR100-R unit and leave the living room out of the system but with an efficiency of up to 70% in a building that struggles to maintain a comfortable temperature already I decided against it. Then I started looking at Boulder and Blauberg’s smaller units but they seem to be inefficient to run. So that brought me to Brookvent’s Aircycle 1.2 (which I have used before in a new build that we did a few years ago and was pretty happy with) but I just can’t shake the feeling that I’m using a sledgehammer to crack a nut. Does anyone have any suggestions or recommendations please. I am trying to keep the spend down (but I don’t want to cut corners) and space is at a premium so the unit needs to be reasonably compact. Thanks, Paul

? Just had a head-scratch moment. When I rechecked I couldn't make the numbers stack up. Realised I was using 70mm as the radius in my calculations rather than 35mm! ?

Fantastic explanation, many thanks indeed Jeremy!

I suppose that the losses associated with the heat exchanger alone should amount to a 10%ish loss in energy (plus ducting losses etc especially as most of the system is located in the cold roof space) but it feels like the heating system is kicking in less often than it used to. Of course that's not scientific, it could just be that we're having milder weather at the moment. I don't think that the MVHR is good at evening temps by extracting the warm air and redistributing it's energy through the vents, I rather suspect that air is being pushed and pulled through areas of the house that had no significant airflow before. Again, not scientific, more just a 'feel'.

Interesting, I haven't come across these before. I presume they use some sort of differentiator to compare two inputs?? A static and a dynamic??

Thanks for that. Makes sense that the cheap AFMs aren't really ideal for accurate measurements of such systems. As my house is quite leaky at the moment I suppose I'm aiming more for proportionally distributing the air flow based upon the room size rather than trying to achieve a particular volume per hour. That said, if I could get somewhere close that would be great. I've just looked at the spec sheet for the UT363S and it quotes a resolution of 0.01 in the range 0-99 (although it maxes out at 30m/s) with an accuracy of +-(5%+0.5m/s) which could put the readings out by as much as 30% so on a typical reading of 2m/s (which at 70mm aperture gives around 110m3 p/h) I could be getting anywhere between about 80 and 140m3 p/h. TBH that's probably close enough for my set up. As long as I'm somewhere around 100m3 p/h rather than 1000m3 p/h I'm a happy chap ?.