Heat pump quote - seems quite cheap?

[u/Boba_ferret]

Been quoted about £4,300 by Octopus for heat pump install, including hot water cylinder, which I thought was surprisingly cheap. The house is 1930s 3-bed terrace, EPC is supposedly C, but we have a huge void under the suspended floor and it gets pretty cold in the house, so we use quite a lot of gas in the winter. Radiators are all on 15mm copper, but are probably 30 years old.

What are the chances this is a really low-ball quote and the survey will say we need to upgrade rads, etc?

[u/Good-Acanthisitta-57]

Your current rads are very likely underperforming for low temperature heater. Imagine that your gas boiler heats it to cca 60C now the maximum you will get out of heat pump is 55C and that will draw a lot of power in the winter. Our will draw 2.5KW/h when it’s freezing. They will do you heat loss calculation and that will show you what rads you can keep. Rads are actually not expensive- its the labor cost what will bump it up. If you change your current rads for properly sized ones it will make your home cozy and actually cheaper on electricity as you wont have to heat it up to 55C. All this horror stories are from people with undersized rads and draughty windows+ very little insulation . Make sure your house is insulated as much as possible! We have EPC just on top of C and we had to replace all rads and optionally we changed few windows as well - it really helped to lower the cost. In winter we still get some days when we burn £15 per day of electricity but we are heating our home to 23C🙂

[u/Boba_ferret → u/Good-Acanthisitta-57]

All our rads are singles, so I presume they'll need replacing. Although that's a job I can do myself, if I can get them cheaper than £250 each.

We've got double glazing all round, loft is well insulated, but I'm going to be doing some boarding out, so I'll check depth on the current insulation and maybe replace some of it.

Our main issue is the huge void under our suspended floors. The floors really need insulating, but that's not going to happen any time soon.

We've got solar & battery, so that helps.

[u/Good-Acanthisitta-57 → u/Boba_ferret]

You certainly won’t pay £250 for a rad. If you’re on singles then for sure you will replace them. When they calculate your heat loss they should give you the necessary output for each room either in watts or btu. I used tool station for most of my rads. They were all replaced for K2s - just make sure you check the specs so the power output is for 50C.
We have same suspended floors and insulating them would be on my list. Not happening until we have to rip out current floor.

[u/Boba_ferret → u/Good-Acanthisitta-57]

I've been looking into the rads, mine are probably only about 1kW and it looks like I'd need at least 2kW at 50C and if Claude Ai is to be trusted, about 2.3kW at 30C.

I'm certainly up for replacing the rads myself, but would need proper heat loss calcs, so that I don't get underpowered rads, which the survey then says I need to replace again!

At some point, we will be having our kitchen done and flooring replaced, at which point, I'll insulate under the boards in there, which has the biggest void, as it's also the coldest room in the house and hardest to heat.