HughF

I’d go for intergas…. Either a heat only or a combi (just set it up to heat only in the settings). As they use a dual path heat exchanger and don’t contain a diverter, you can use nearly any of their combis as a heat only.

That was my understanding of rauthermex from the data sheet. It appears to be a fully bonded product unlike the uponor which looks like it allows for the cores to slip as you bend it. I need to do 2 90’s but they can be wide sweeps as they’re in the garden at one end and under the floor at the other. I can come out the ground at 45 at one end and transition to 32mlcp for the hidden run alongside the shed.

I need approximately 18-20m of insulated twin ducted pipe for my ashp flow and return. Rehau rauthermex duo seems to be much cheaper than the uponor product and is slimmer overall at 110mm for the 2x32 duo. Does anyone have any recommendations either way about what to use?

Fair point…. I guess it depends on whether the heat pump goes up the garden or against the wall. Against the wall then the flow and return can punch through the 2 courses of block work below dpc and end up in the insulation layer. If up the garden then I’ll buy £1k worth of twin insulated 32mm and bring it right into the house under the floor void. Quicker, easier, less figuring out to do.

If you batch fire the 355 in the shoulder months then I would suggest you fit a flap type non return valve, with the spring removed, in the hot side of the gravity loop. This will prevent thermosyphoning back through the Rayburn when the fire is out and the TS is hot. If you have a long distance between the 355 and the TS then you might want to consider siting the laddomat at the TS. That way when the stat opens in the laddomat it won’t push a huge slug of cold water into the top of the TS. I’ve helped my Dutch friends with a similar install to this, 355 and a polish 50kW peat burner (think beeston sectional domestic) firing direct into a pair of close coupled 800ltr buffers. 4 mixed zones off the buffer, solar coil in the base of one and DHW coil in the top of the other. Endless free hardwood pallets fuel their heating system.

I ended up putting 10mm swa and 16mm mlcp down the same 40mm duct. After the trench was backfilled SWMBO insisted on a water supply to the shed. It was bloody hard work pulling them through. I thought we weren’t going to manage it actually. There were 3x 90s to go round.

I don’t have any walls to run it in, the extension is open plan… It has to go in the floor, I just need advice on which part of the floor to put it in. I’m leaning towards either in the insulation layer (along with the ducts for the ventilation of the existing suspended floor void) or in the type1 layer. Either way I’m going to need to come through or below the footing.

A couple of sketches. The ashp will either go on the wall, or up the garden. I’d prefer the up the garden option, as would my wife. It would be 15m of underground twin ducting though.

It’s a full width rear extension, and I detest externally exposed pipe work even when boxed in. I also can’t bring it up the side of the house as I the joists run the wrong way. I’ll do a drawing to explain it better.

Ah, a posh version of my system in Dorset. Except I’ve got a stainless back boiler in a mk1 Rayburn. And no central heating 😉 The only thing I would add: please fit a laddomat to that 355. The back boilers are weak, and complicated/expensive to replace. The 355 doesn’t like being taken apart to have it changed. Not the finest Rayburn, but certainly the most capable.

I’m putting on a single storey rear extension and need to bring the 28mm flow and return for the ashp through the floor of the new extension from the garden, and then up the now inside wall of the house before punching through the cavity wall at first floor level to run towards the cylinder cupboard in the middle of the house. I can’t box in at skirting height as I’d need to cross a doorway, so it needs to come across the slab, which will have ufh in it. Should I make up a trench with shuttering and pour around that, and then board over it (my neighbours did this when they relocated their boiler to their new rear extension)? I could follow the perimeter of the slab so to avoid crossing the ufh. Or should I do something fancy with coming through the type1 layer that’s at the bottom of my floor design? I am already planning to come across the garden with some insulated twin ducting, I suppose I could carry that through the founds and up out the slab?

Not as much as a (decent) gas boiler….. there are two schools of thought, size it perfectly to the load and run the fan and compressor at maximum or oversize it and run the fan and compressor slower. I’m going for the latter, buying a 9kW (peak) unit for a 6.7kW modelled heat loss.

Been getting used to using concepts on the iPad for sketching, this is the planned floor detail.

Done a quick sketch, anyone care to comment? Single manifold set shown for the rads, I’ll probably have one upstairs and one downstairs.

I’m probably going to install one of these at my boss’ house soon to heat and dehumidify a downstairs room. They look just the job. And no F-gas requirement

No trvs for us. the doors are always open to all the rooms, the house is tiny and we don’t have the luxury of unused rooms 🤣

Assume that you meant 'So the return water out of the rads if no UFH is on would flow direct back to the ASHP'? The setup with close-coupled T's in the return line makes perfect sense, cheers. I'll design around this. I was planning on having all the heating emitters on a single zone but manifold plumbed, just so I can easily balance at the manifold (I have the manifolds already, and all the mlcp pipe)....

I'm a real fan of the concept of the Homely thermostat but the lack of non-cloud control and a decent in-home, physical front end is putting me off. It's either smartphone or smartphone... Agree with you about the lack of cooling on the Vaillant - seems an oversight to make it so complicated to enable.

I'm going for UFH in 100mm slab in the extension (south facing), tied to the mesh on 50mm stilts, new rads in the rest of the house (as it's a retrofit)... Whole lot will be driven from a 9kW (max) ASHP running in weather comp mode. I can't size the rads for the UFH flow temp so I'm going to set the weather comp up to suit the rad sizing then use a blending valve and pump station at the UFH termination. I want to do this without a LLH or buffer if possible (for efficiency and space constraints) but I'm pretty sure I'm going to need at least some sort of hydraulic separation between the different flow rate emitters. Anyone have any input on this? Should I make allowances in the design for a buffer or LLH?

Care to tell us what ashp you’ve bought? We can check the specs to see what it’s minimum output is. What flow temp has the heating system been designed for ?

Yeah, it’s scrap. Unless you’ve got f-gas, some leak spray and a brazing torch…. To be honest if it’s sub £100 it could be a good donor for parts to make up something custom.

And by comparison, the non-heat pump vaillant cylinder of the same 150ltr capacity is 0.69m2 coil area. The 300ltr only gets a 0.8m2 coil.

1.5m2 is fine for a heat pump coil. Ideally you’d see 2m2 or above but sometimes you just can’t get that size into the cylinder. My vaillant slimline heat pump cylinder is 1.5m2.

I think the target customer is the person who has an average house, and just wants a smart thermostat. And/or installers who don’t want to have to come back and tweak the weather comp curves, or try and get the customer to do it from an archaic controller. Because it is smart, it can learn the thermal response of the property and the emitters, therefore it can offer load comp on heatpumps that don’t have it in their native controller and then revert to weather comp automatically if the property is permanently occupied. It can also make a decision based on energy pricing at the time that heat is called for. yes it is another walled garden but having in essence an iot modbus interface to the heat generator, and controlling the flow temp from the smarts in the cloud, I can really see the opportunity for optimum control and cost savings. I agree that more integrations would be good and from talking to their engineers on the stand, they were totally on board with adding more heat pumps to the list. Midea and Samsung are supported for now because Graham Hendra consults for them. They were happy to talk to cool energy about adding support their carel based units.

Park on double yellows outside, get the ticket, stick it on the bill. I know that’s what Thomas Nagy used to do in rbkc. They’d only ticket once, you’d have the van outside all day, and it was reduced to £30 within 30 days or something. Less than a days parking.