I would try switching them off, might be ok without them. If not the add insulation and 3g not forgetting to do the draughtproofing

My thoughts would be:

- you will need heating on the first floor almost certainly, especially as you prob won't take the insulation levels and air tighness levels to a point to negate heating.
- you've alerady got a CH system, so unless you particularly WANT UFH, then make use of what's there (pipework wise) assuming it's 15mm and not mini or micro bore. Will need a flush through.
- you could take a risk and cap the existing pipework in the wall/below floor, for a future rad installation in each room, and have a decent sized rad in the landing, but unless you keep bedroom doors open, the rooms will get cold. If you've anyone siting in the bedrooms, studying/reading/on computers, they will be uncomfortable at less than 19/20oC, which is warmer than normal sleeping temps of say 17oC, so you'll need to cater for that.
- I personally think UFH on upper floors is often overkill (carpets/beds/wardrobes covering floor), and a lot of work, but it's not wrong. Often people want a quick burst of heat just before they wake up, not constant heat all day, so UFH isn't ideal for that scenario. Ditto, quick heat before bedtime (studying time) but not so warm for sleeping.
- determine how you're going to insulate (what's possible/not detrimentalto the fabric/but to a decent level), and therefore you can calc the heatloss per room. Not difficult.
- size the rads for say 20oC delta T (say 40oC water off ASHP)
- hopefully with the reduced heatloss thru insualtion, draft proofing etc, you won't need much bigger rads than existing, but caluclate it, don't guess.
- you won't get a consistent answer on GBF about 2G versus 3G, because there are various good arguements for both, which likely means you won't be wrong doing either. I like 3G, but 2G is good too, and often provide that for clients. There is a lot of heat loss thru windows at Uval of 1.2, versus walls of say 0.17, so windows in gerenal are weak points, but making the energy saving case versus cost to buy 3G is not easy. It's a comfort thing for me, but then the grid is getting greener, and your consumption less with an ASHP, so pick one and go with it. How the window is fitted prob will have a bigger impact.
- I would go for simple approaches to heating, insulation, draught proofing, and do it well, as you'll run out of cash/enthusiasm/patience if you try to be to idealistic. It's somewhere to have time to live, not a scientific experiment

Thankyou GP for your detailed response.

It's a difficult one, as the floor has to come to to up anyway for the rewire, the copper is 15mm to each rear but I'm thinking while I'm in there just to replace it all with new. I've dealt with far too many leaks through work where old pipework leaks.

So may as well upgrade heating elements. What's the best website for heatloss calculations?

https://www.heatgeek.com/how-to-size-my-heat-pump-or-boiler-heat-loss-cheat-sheet/

Use the cheat sheet here to guesstimate the heat loss per room

Multiply that by 3 to get the radiator sizes (because you will be running at much lower temperature than they are rated at)

Much more good stuff on his website and YouTube channel.

Radiators are remarkably cheap now, especially if you round up to the standard 900 1200 or 1800mm K2 sizes, so lean towards oversizing them.

Posted By: GreenPaddyI add on a nominal 20% to the rad sizing, as you need to be able to increase room temp, not just maintain it.

That doesn't necessarily require oversizing. When room temp is lower than desired/design temp, the delta-t (temp difference between rad water and room air) will be greater therefore heat output in surplus, proportionately, declining to normal as air temp rises. Not by a lot, admittedly, with trad 60o flow temp, but becomes a more significant surplus with large rads/lower design flow temp, till with UFH the surplus is so effective that room stat/TRV is not necessary.

going for a flat rate / m2 doesn't do a very good job. Too many variables to upset the flat rate.
The amount of external wall area vs. the floor area
The window area (and type)
Floor and / or ceiling thermal values
Designed flow rate and flow temp.

All of the above will conspire to invalidate a flat rate sizing attempt. (and probably more that I have forgotten)

There are lots of calculators around and it doesn't take long to do the job properly i.e. room by room calculations

If there's a gain for one room, there'll be the exact same loss for the other room. If you're using excel it's easy to do a calc for each wall of each room

Correct, you don't normally calculate internal walls. Calculations assume the house is kept at the same temp. throughout so there will be no loss or gain through internal walls since each side is at the same temp. so no heat transfer.

The heat transmission through internal walls in our MCS room-by-room calcs was 10s of Watts, negligible compared to the 100s of Watts of transmission by air flow from one room to another. The different air change rates used for each room, were entirely made up by MCS as nobody has room-by-room air leakage test data.

So in other words, don't sweat the details, this exercise is all a big guestimate anyway.

On the plus side, Screwfix sell their 2kW radiators for only £11 more than their 1.4kW radiators. So don't worry just buy the biggest radiator that fits the space and you can run them much cooler and still get hundreds of Watts out of them.

Interesting, looking back at our MCS calc for the bathroom (6m2 floor) they said

45W through internal walls (8% of total)
107W through external walls and windows
385W due to 3ACH ventilation with external air at -4deg

Total radiator 537 W


But it seems to me that most of the ventilation that is extracted from the bathroom, is 18deg air that is sucked into the bathroom from other rooms (door is undercut). So much of the 385W ventilation heat should come from the other rooms' radiators, not the bathroom's. The bathroom radiator just tops it up to 21deg.

So bathroom radiator load should be nearer 200W and other rooms should be increased accordingly.


We have at least a 1kW radiator in every room, so don't worry about it at all :-)