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With MVHR fitted, is it recommended to use a hob extractor that is vented to outside, or should you only consider a recirculation style of extractor please? Thanks, Steve.

Hi, It was planned to vent the cooker hob to the outside... but it can be changed if it will cause issues? Where are the dead zones please?

Thanks again for the replies. Please find attached version 2 for further comment. Hopefully this has captured most of the comments where it is possible. I have removed 2 supplies from downstairs as I think they were redundant when considering air-flow. Let me know your thoughts please! Steve. MVHR Design v2.pdf

Thanks for the great advice above. With vaulted ceilings and block and beam construction the duct routes are proving a bit tricky! I will update my provisional design to v2 for further comments. Thanks again, Steve.

Hi and thanks for your reply. The showers will definitely get used the most so I will reposition extracts accordingly. Should they be within the shower cubicle footprint please? Are my supply nozzles too close to the internal or external doors (or both!) please? If you do not plan on opening windows, and they are not fitted with trickle vents, is there an issue with positioning supply or extract nozzles next to windows please? I am fitting a local, surface mounted kitchen extract unit to try and capture smells. The ceiling height above the hob is >4m so not sure if grease will be an issue? What do you think? A second unit would certainly help with the length of ductwork but I have no obvious place to install it. Thanks again, Steve.

Hi Conor, Thanks for your reply. The upstairs outlets were positioned to shorten the duct routes as far as possible, as with the bedrooms having vaulted ceilings, the ducts will be routed along the ridge above the bed and I was/am concerned about noise. Am I being overly concerned about noise? If so, I will modify the design. The hallway is probably not going to be screened off from the dining area so will be one big open-plan room bro put a inlet in there. The routes taken are generally following the beams (I have block & beam floor construction) downstairs and are where I can hide ductwork upstairs. On your other points: 1. What size duct work are you using please? 5. I was told that I would require fire stopping but will check again. 8. I was told to keep extract points away from the shower area, which seemed a little counterintuitive. I take it you've had no issues with the points near to your shower? Thanks again, Steve.

Hi All, I have completed an initial design of my MVHR for my New-Build with the following philosophy / design criteria: One unit fitted as centrally as possible (within the garage) for cost, ease of set-up, as well as lack of options for a second unit due to vaulted ceilings throughout the property. (Note: I am aware that ducts passing from garage in to living area will require fire collars/stopping). Radial system design to avoid crosstalk. Large diameter pipes (90mm?) to reduce velocity and therefore noise. 2 x ducts used for longer runs. (indicated by a "2" on the intake/extract positions on attached design) The position of the intakes and extracts have been positioned where it is possible to get duct runs so may not be 100% ideal but I think are a reasonable compromise. Please feel free to critique my attached design or the above design philosophy! Questions I have please: With 90mm ducting, at what distance should I consider 2 x ducts to an extract/intake point, if at all, please? What ducting would you suggest using? Is there any issue with having intake and/or extracts on walls rather than ceilings please? I have had poor service from BPC with them not responding to several emails. Any other suggestions for suppliers please? Other than fire stopping, is there anything I need to consider with putting the MVHR unit in the garage please? Recommendations on unit manufacturers please? (Zehnder appear to be a popular choice, but stock seems limited at present!?) If 2 x ducts are used for longer runs do they go to separate intake/extract points or to the same point please? Anything else you think I should consider please? Many thanks for your help, Steve. MVHR Design v1.pdf

Thanks for the reply. I will adjust as ACH to <1, but where do I enter the “leakiness” of my property please?

Thanks for your reply. There were a couple of parameters that made a big difference to the heat loss, those being; air changes per hour and MVHR efficiency. I set the ACH to 3 as I think this refers to the leakage through the building fabric? If this is correct, I believe 3 ACH is achievable, and maybe I can improve on this through some of the advice I have recently read on this forum. Having spoken with the guys that will be completing my air-testing they have advised that a wet plaster will certainly help with leakage so this is a route I will take. Unfortunately the insulation is already fitted in the floors and in the walls, however I am trying to improve the U-values for the roof as the insulation is yet to be fitted here!

Hi All, I have completed my heat loss calcs for my new-build using Jeremy's spreadsheet (many thanks Jeremy!) however I would like a little help in interpreting the results please. From the spreadsheet I am hoping to size an ASHP, which will be the only source of heating for the house expect 2 x log-burners. (Note: there is no mains gas to the property). Any help in interpreting the results as well as a sense-check on the figures used would be gratefully received. Kind Regards, Steve. Heat loss calculator - Hereford House.xlsx

Thanks for sending through. I have just read on here that, as I have used a breathable membrane, I do not require an air gap, therefore I could use 150mm mineral wool between rafters and then PIR beneath the rafters. I have exposed oak trusses so the maximum thickness I can go to beneath the rafters, including the plasterboard is 80mm. Would the above give a U-Value that Building Control would accept? Is there any reason not to fasten insulation to the underside of the timbers and then fasten plasterboard to the insulation as this looks a cheaper solution than insulated plasterboard but is effectively the same? Or is it!? Also, looking at the above you have sent through, can you help me understand when and where vapour barriers go please? Thanks, Steve.

As my rafters are 170mm deep, `I can fit a maximum of 120mm of insulation between then to give a 50mm air gap. Mineral wool, or equivalent, I assume would be much easier to fit than PIR and, again I assume, will be easier to get much closer fitting (less air gaps), but the U-values are higher than for the same depth of PIR. I am open to suggestions though!

The roof is on.

I have vaulted ceilings - would this lend itself to a mineral wool installation please? For information, the rafters are 170mm deep, therefore allowing a 20mm air gap, I can fit up to 150mm of insulation between the rafters. I can also add up to 80mm of insulated plasterboard beneath the rafters. I was advised by the architect not to fit insulation on the 1st floor which is a block and beam construction. Was this good advice please?

Could you point me in the right direction for the post you are referring to please? Many Thanks, Steve.

The updated 150mm centre design is to use 2 x manifolds downstairs which will help avoid the congestion you mention.

Thanks for the reply Dave. I will complete a heat loss calc for the individual rooms. It is good to know that there is no detriment to 150mm spacing, other than cost. It is a steep learning curve for me at present!

Hi Steamy Tea, Unfortunately I have not been given the heat-loss calcs by the company that completed the first design. I was pointed in the direction of a heat-loss calculation tool last night that a lot of people have used on here that will hopefully help me estimate the heat loss. I do have the SAP report but do not fully understand it at present... The heat-source specified was a 12kW GSHP.

Hi Dave, in the design using 200mm spacing it was suggested I would need supplementary heating in the bathrooms as the desired temperatures could not be achieved. I am assuming, but happy to be corrected, that reducing the centres in these rooms will increase heat output and I therefore may not need additional heating? I am expecting the design anytime now and will be happy to post for critique.

I have just had an UFH design completed by the screeding guys as the previous design appeared to have lots of issues i.e. 200mm centres and pipe runs way in excess of 100m. Did you also calculate the size of your ASHP, buffer tank, etc or did you get a company to complete this please? I ask as there seems to be a great disparity in the quality of the quotes and information I am receiving. All good fun though!

It is to the point in the build where the only insulation I can increase is in the roof. I assume the advice would have been to increase the insulation if I could have?

Who completed the design of the system for you please or is this something you did yourself? @Conor PS. I have found the heat loss calculator - many thanks for the heads up.

Thanks for your replies gents. I will have a go with the heat loss calculator tomorrow. Out of interest Conor, have you selected the manufacturer of your ASHP please? If so, what have you selected and why?

Thanks for the reply ProDave. The GSHP was sized by NuHeat, but after reading on here, 12kW seems much bigger than most are using. I am aware that the house is only ‘reasonably’ well insulated compared to what others have, however I am just wanting to check that 12kW is the correct size unit for the size and type of construction of my new-build? Hopefully supply with return to some form of normality once the RHI deadline has passed.

Hi, I am new to the forum so please be kind! Having recently been advised that there are supply issues with my GSHP I stumbled across this forum whilst searching for an alternative supplier. After lots of reading on this forum I am now swayed towards an ASHP. My original GSHP design proposed a 12kW unit therefore am I correct in assuming (if the calcs were right!) that I would exchange the 12kW GSHP for a 12kW ASHP? The property is c. 350m2 with the following level of insulation: 100mm PIR in 150mm cavity walls. 100mm PIR underfloor. 170mm PIR (TBC) in roof (cold-construction). I have had a SAP report completed however, I do not understand how the report can help me in sizing my heat pump, if this is indeed possible therefore any help on sizing a ASHP would be much appreciated? Kind Regards, Steve.