Beelbeebub

The "only" problem with r290 is it's flammability. In practical terms it's not a problem. The amounts are less than a camping gas cylinder. But from a regulatory POV it's unlikely fitting will be allowed without some sort of qualification. Whether that is an extension to the fgas certification or the gas safe certification is another question.

Sensible. It woukd be extremely close to the wind if the same installer reconnected the old boiler. Wouldn't be on the installer if the customer got a different heating engineer to reconnect the boiler. Of course the customer might be in hot water (ha), but there isn't a requirement that once a HP is fitted and a grant issued that property can never again have a boiler fitted. HP installs go wrong, fail, customers decide they don't like the noise etc.

Yes, if you have a HP that can easily integrate then it's an option. As for not getting a grant, I was discussing with some installers. There is nothing in the regulations that say you have to physically remove the existing boiler, only that it cannot be part of the system if you want the grant. Equally there is nothing to stop the customer contracting a heating engineer to integrate a boiler with the existing HP, say a month after installation and after the grant process is complete.....

That's fair enough and a good point. Different people ha e different preferences and tolerances. My mate can't stand UFH. Even when he was putting a new slab floor in his place and could have chucked in some ufh popes for let tile extra he was adamant he didn't want it. The floor in their house is bloody freezing and they all wear slippers, which they like. <shrugs> A2A emitters are far from perfect, especially as they are primarily designed for cooling, hence their high wall location and aggressive blowing. Maybe with hearing being the focus more low wall "radiator" type units with a gentle waft will become availible. The key point is hybrid systems *integrate* with the existing wet heating system. There is still a considerable amount of replumbing needed (low loss headers, control systems etc) and if you don't update the radiators for the lower temps your HP will be less effective. The only system that looks like it might plug in is the Alpha, where the unit piggybacks onto any primary return, but I'm not sure if you need to have their boiler anyway. Sticking an A2W system in leaves the wet heating system totally untouched. Indeed many people have already done this when they fitted air con after last year's heatwave. Admittedly this might be slightly less true if you were looking to put in low wall units as they would be competing with radiators for wall space. If sutible designed for heating emitters could be made readily available it would make sense (from a national perspective) to push these units on a par with a2w eg same treatment for grants, planning etc. My understanding is there is a reluctance to promote them as they are seen as cooling and therefore an additional "luxury" drain on the grid

If I'm honest, air to air looks like a better route from a technical POV. If we could make the VFR layout the default so you just need to pipe up from emitter to emitter it light be a winner. It would make sense from a national perspective. A2A systems could be installed without touching the existing gas/oil system and run in tandem. This negates the "throwing out a perfectly good boiler" argument. It also puts the users mind at rest about "what if it costs more or we have a super cold snap" The user could then choose whichever system they found best for their comfort, use and cost perspective. It wouldn't necessarily do DHW, but again that might be a plus. There wouldn't be the cost and space issues of fitting a tank. The existing system can trundle on as is and maybe replaced at a later date with a new tank if/when the user is convinced. The installs are likely to be cheaper and easier too.

Yeah, this is the problem. Wet fan coils are very bulky and industrial and often very expensive Refrigerant fan coils are cheaper, better looking and have better performance There is some physics behind refridgerant fan coils being able to be smaller and more compact and the economics of scale are pretty compelling when it comes to price and choice. Discreet fan assisted conector radiators like the stelrad version (basically a bunch of PC fans strapped to a conventional radiator) might have some merit.

But if you are going the fan coil route, why not ditch the middle man and go a2a multisplit? The head units for those are far more developed and mass manufactured than water based fan coils.

How about this type of kit? https://www.epicair.co.uk/collections/airflow-airflex-semi-rigid-ducting There are 75mm round and 115x51 oval ducts. They have ceiling and floor plenum outlets. We have the older version with metal plenums, you could wall mount them between studs and run 2x 75mm round (or use oval) to each one in a radial scheme. Or you could mount them through the floor (I think they have specific ones for that) It was a pretty easy system to use, just drag the pipe off the coil, cut to length and stick in socket. The radial scheme has more pipes, but they are smaller and you don't have to worry about sizing down as the run goes on or about inter room sound as much.

If you are happy to work under the floor then go for it! Too claustrophobic for me (plus I'm over 6ft and tend towards solid than skinny). The Americans do use the dates with carpet. Usually several around the perimeter, especially under windows. They also (sometimes) have them in walls low down, you could come up from below inbetween some studs and then through the wall with a decorative grate... Though, if you were a fan of the X files you might not be too keen!

If you have easy access to underfloor and it's clear just use the same insulated ducting and terminals for loft routing but under the floor. You'll probably need to put some boxing in underneath to support the ducts. If you have a timber suspended floor with a good clearance then lift some boards and create a plywood box between and under the joists. Then lay the duct into that. Then use standard duct terminations in corners and the like.

If it's a bungow, presumably with a loft, running the ducting in the loft is the obvious solution - far easier to install and maintain. TBH, why not just a mutki split with the pipework running through the loft and then to a standard head unit? Super neat and pretty standard.

The big stumbling block is the low specific heat of air. If you assume an inlet temp of 40C (ie 20C above room) you need about 200m3/hr to provide 1kw. In context that's roughly the flow from a fairly powerful 125mm bathroom extractor. You could have hotter air (as I believe the Americans do as their air heating systems are gas powered) which drops the flow, or huge ducts....

Pump the air into the underfloor space and have gappy floorboards? 😁

Maybe some a2a HPs with the cooling function disabled in would be a sales opportunity in the UK. I get the idea behind not encouraging cooling systems but with the way things are going it may be shortsighted Maybe if the a2a HPs carry an approval which is only given to models which either can't cool or can only cool down to (say) 28C. That way you can cool the house in an extreme heatwave but it's not going to be used for general cooling

I think, if you order online, you are covered by the distance selling regs. 14 day no quibble right to cancel and return even if packaging is opened (you do have to pay for carriage) You have the right to handle the goods as you would in a shop, though not to use them beyond what you would in a shop. So you could wear some shoes and walk around inside a bit, or put some gloves on. But you can't wear the clothes out for a night or use the gloves for some gardening. For a HP I would argue you can get it out of the box, look at the connectors, go through the manuals maybe offer it to it's location. But you can't actually start to fit it, fill it up or run it. If you do, your refund right woukd be based on it being faulty or not as described.

I'm weighing up Fgas as I have a large number of retrofits to do. The industry does seem to be heading for monoblock, the primary advantage of which is no need for Fgas. The supposed other advantage is that it"plugs in" to our existing dominant heating system (wet radiators), but that is debatable as many retrofits (which will be the majority) also require changes to that system (bigger rads, pipes etc) I can see that going the air to air route whilst needing a complete system install (all new pipework, emitters etc) would allow for "overlaying" the HP system over the existing boiler & rads setup. This has a couple of advantages - no disruption to existing heating hot water system, so can be installed in cold seasons - no need to wait until existing system needs replacement - no worries about new system being "insufficient" as old system is there as backup - for combi systems no need to install a tank initially - no worries about HP not being able to cope with cold snaps or being more expensive to run. - cooling in summer Our current antipathy to air to air seems to be born from a British distrust of air-conditioning rather than anything else.

I'm sure I saw someone doing vinyl wrapping of heat pumps. Same technique as they use for vehicles I guess, but they don't need to disassemble to do it.

But indicative of thinking. The big advantage of gas is the installer doesn't have to think too hard about specifying it. Aside from huge houses pretty much any boiler will work. A 12kw boiler is about the smallest you can buy and that will do most houses. An 18 or 20+ will do all but the biggest or leakiest houses. If you over specify, they can turn down for the smaller property or just cycle more. If the rads are a bit too small or pipes too skinny just wack up the flow temp. The physical box is pretty much always the same size as the old one. So if you want an easy install with little chance of call back - gas boiler.

Yeah local numbers merchants have one on display but warned me "unless you fit it to a new build you'll be cold"

Have you looked at Kaisai? Despite their name they appear to be based (or at least have local. HQ) in Poland https://kaisai.com/new-series-of-kaisai-khy-heat-pumps-with-r290-refrigerant Somewhere on their website they have the manuals and some very comprehensive performance tables Edit: They seem to have updated their website, they also seem to have switched up the models offered (12/15kw vs 9/14 previously) Anyway I have the old manual stored which has some useful data tables they don't seem to have up now. Due to size I've chopped the back half off with control panel instructions and parts lists Kaisai 1st half .pdf

Yeah, pretty much this. I'm thinking a coup that can do 15kw at boiler temps, should be able to transfer 3 or 4kw even at the lower delta T of a HP. The only issue might be the flow rate achievable as boilers tend to flow less at higher temps, but the coils are almost always 22mm so that shouldn't be an issue if the HP and cylinder are relatively close. The only other thing that might cause issues would be if the coil geometry was different for HPs and boilers. I'm mainly thinking about the vertical distribution of the coil, but wouldn't both be best with the coil as biased towards the bottom as possible? The idea is to replace the boiler with the cylinder (actually put the cylinder above where the boiler was as it's above the worktop so the extra stickout would be a problem but it's a tall room so we could put it on top. The HP will be on the wall just outside and the pipes will come through the existing flue hole (the walls are about 500mm thick hard bricks as it's the lower part of a tall building so avoiding drilling holes is good!) All the HP compatible cylinders I've seen seem to be 125l plus and too tall to fit into the space available.

If I fitted the UVC, it comes with an immersion so I could use that startetgy as a fall back. Problem with night tariffs is the day tariff tends to be much higher so the HP gets more expensive to run.

OK, so I've got a boiler coming towards end of life for a small 1 bed flat. I was toying with replacing with a small HP. The problem, as ever, is the hot water. Space is limited. I was thinking of a 90l cylinder to be high mounted out of the way. There are a range of cylinders availible but none seem to be marked as heat pump specific. However, the coil ratings on meany of them are pretty high anyway, eg 15kw. The rationale for a heatpump specific cylinder is you need a greater coil area to get efficient heat transfer at lower flow temps, and greater flow. But the HP would only be 6kw nominal, so in DHW mode it would be punting out a bit less say 5kw. Obviously I would derate the coil for the lower HP flow temp, but would using a 15kw coil to transfer 5kw at a lower temp be OK? Or is there another difference between standard and HP coils, like coil position? The other option is i save the £500 or so on the UVC and spend it on an instantaneous direct electric heater, the property has a kitchen sink, a basin and a shower. So only the shower is a big draw and 10kw would just about do it. Slightly less efficient but potentially alot easier.

Agreed but from a practical POV, a DHW tank is a bulky item costing about the same as a boiler with a defined capacity, which makes them a bit of a backwards for the end user vs a combi. Which is unfortunate

Depends (in both cases) on the size of the collector loop/flown rate. Specific heat of water is roughly 4kj per kg per kelvin. So 20 kW would be 1kg per second by 5k (say 10C to 5C) Or 60lpm a fairly high flow but not totally impossible. But it would be a mad idea as you would be massively over sizing your system for a very nich situation. Gas boilers are very easy to oversize hence the ease of creating combis. For HPs we need to get back to (unfortunately) stored hot water.