ASHP design and BUS eligibility

NedS

https://forums.moneysavingexpert.com/discussion/comment/81882847#Comment_81882847

Absolutely, if that room is already too warm with existing radiators at flow temps of 45C it sounds like the existing radiators (at least in that room) do not need replacing, although as others have said may benefit from being replaced, if that was possible.

If it's not possible / convenient (and you are clearly aware of the potential benefits), then I'd point out to your system designer that room is already too warm running at 45C flow temps with existing radiators, and maybe they can adjust their assumptions and calculations to bring it in within the MCS specs. In my mind there is wiggle room in the process, it all depends on how flexible the system designer is prepared to be in working with you (for example, changing the ACH assumptions can make a huge difference to the heat loss figures, and thus the required radiator sizes and design flow temps. A little bit of flexibility around assumptions, especially where you have empirical evidence to support, can still allow that MCS box to be ticked.

tfhnota

I think someone said the MCS calculation is based on the needs of the house not the people living in it, as the next purchasers may not be so tolerant to lack of heat.

greenbee

Having spent some time working through the paperwork, I think that we can work with all the current radiators at a 55C design temp. The plan then being to have details of radiator size requirements for each room at 35C so that if any work is done we know what to replace them with so we can gradually reduce the flow temperature.

Heat loss is calculated at 11.3kW, 14kW heat pump specified - design is currently for 40C flow temp, but he's given the outputs of the radiators at different flow temps, so we can probably tweak it. I think my biggest reservation at this point is that he only installs Mitsubishi so I need to do some research - or talk to a different installer (there's a possibility that the guy who did a neighbour's installation might be available, and he definitely takes client input onboard). The model he's specified can modulate down to 6.5kW - and heat loss

The whole thing is complicated by needing to install the UFH in the garage conversion whenever that fits into the build project, and the kitchen radiators whenever the kitchen is ready to be done. So it's not a one-off job. (I should probably find someone willing to do the kitchen plumbing and install a whole house water filter too really!).

matt_drummer

Gradually increasing radiator size room by room will not work as you are anticipating.

You can't just add a bigger radiator and then reduce the flow temperature a little until you have done them all.

The flow temperature of the water is the same to all radiators/ufh so if you make one bigger and reduce the flow temperature the other radiators won't put out as much heat as they used to. Those rooms will be cooler.

If you increase the flow temperature the the room with the bigger radiator will be too hot.

And if you think trvs will solve the issue, they will, but they will create another.

greenbee

The majority of the rooms have suitable emitters for 35C (either UFH or radiators), so a better way of putting it is that some rooms will be too hot and a few on the cool side until the last few are done. But the plan for the building work that's starting in the next few weeks means that all but two rooms will be sorted by the end of the year.

The two rooms that will technically not have big enough emitters may actually be OK, as one of them at least is always warmer than the rest of the ground floor (which suffers from being mostly open plan, with no heating in the original kitchen, so the UFH in the living space is trying to heat twice the space it is supposed to, while the radiator in the old dining room is zoned and controlled separately to the UFH). It also has a wood burner, which tends to be used if we are in there. The small room is rarely used at present (maybe we should make it into a guest room for people who we don't want to get too comfortable!).

Undoing the four zones (three downstairs) and adding heating to the kitchen should make a significant difference. A couple of the bathrooms may be on the cool side, although the boiler has been set at 45C all winter and they've been very warm, which is why we're not worried about them.

Given how long it has taken us to get the current heating to be even vaguely comfortable, we're not worried about taking our time to get it right. But we do want to make sure that the heat pump itself is correctly sized as that's the bit that can't easily be changed once it's in.

Reed_Richards

https://forums.moneysavingexpert.com/discussion/comment/81882847#Comment_81882847

Can you explain this more fully? I had to replace most of my radiators but these were mostly single panel single convector radiators that were replaced with double panel double convector types. The wall space occupied by the new radiators was pretty much the same as the wall space occupied by the old ones. There was very little disruption, no upheaval and the requirement to make good afterwards was minimal.

greenbee

The rads in question would go from K2 to K3. K3s are pretty chunky. I’d also need to empty and move bookcases and furniture to make room for the work to be done, as well as arranging for the decorator to spray the radiators once installed otherwise they’ll look odd. Given the amount of work we will be doing this year, clearing an additional room would leave us with no living space and present us with a storage issue. While it may be a small thing for some, it’s just one thing to many for us to have to deal with at the moment with everything else we have on.

Reed_Richards

K2s already; that's a shame. My rads must have been installed when my bungalow was built so I guess the prime consideration was saving money and never mind the amount of wall space the radiators needed. But when you do come to install new radiators see if the installers would allow you to spray paint them first; if you are going to paint them then before they are installed must be the best time

Alnat1

Maybe it's just me but I didn't know painting radiators was still a thing. It's something my dad did in the 70s/80s. None of the radiators are painted in my house.

greenbee

Thanks @therealdeal47. I've reviewed the paperwork, and think I can make it work as long as the installer agrees (it'll have to be done in bits anyway, as some of it is affected by a garage conversion and kitchen refurb). I'm now trying to decide whether to be sensible and get a second proposal before making a final decision.

I have less than 300l of oil left, so need to decide soon!