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1.There is the guarantee if you need it dont worry.
2.ΔT50 only refers to the radiator spec but yours will be taken at lower figure.(not mentioned anywhere on the document)
3.Heat geek taken the whole house radiators combined as heat flows from hot to cold so there should be equalisation.
To me this shows that they are, as I suggested up thread, winging it a bit/playing the numbers game based on their accumulated experience.
We don't ask for detailed design specs of a car engine, we ask how many miles per kWh it does (or per gallon for fossil cars). It's thus only a matter of conditioning that we ask for heat pumps. Given the state of the industry it's sensible conditioning, but in a more mature industry it would be unnecessary.
Ultimately only you can decide if you are happy with this. If other similarly priced quotes involve replacing more radiators and are otherwise similar technically you can be pretty certain that these will in fact deliver a higher scop
That is unless they are both under estimated, the Heat Geek guarantee is invoked, and the result is that they are forced to better the alternative at no cost to you.
Unfortunately the underlying problem, which is not readily fixable, is that heat loss estimates have a significant degree of uncertainty attached to them.
@l8againagain I think you need to look into it in depth.Heat geek proposal says the heat loss are for -3.6 deg C outdoor and 21 deg C indoor temp
Vaillant spec for 5kW attached shows the unit can indeed do 6.4kW (my heat loss according to heat geek). But they can do 6.4kW at -3 deg c only if flow temp is 40deg C or below.
My existing T11 radiators cannot output 6.4kW at 40deg C.
Not overthinking here. My exisitng radiators wont work with 5kW unit from Vaillant for 6.4kW heat loss
@jo2255, you’re absolutely on the money here IMO. This isn’t overthinking it... you’re simply checking whether both sides of the design work at the same time, and this is something honestly makes my head hurt.
The Vaillant table you provided shows the 5kW unit producing 6.4kW at -3C only when the flow temperature is 40C. Your design temperature is actually slightly colder at -3.6C, so even that operating point looks marginal. Once the flow rises to 45C, the available output drops to 6.1kW, then to 5.9kW at 50C and 5.8kW at 55C.
Meanwhile, your radiators cannot emit the required 6.4kW with a 40C flow. Based on the figures you previously posted, a conventional radiator correction calculation would put their combined output at only a fraction of that figure. They would appear to need a flow temperature somewhere around the high 50s or 60s to meet the stated heat loss, but at that temperature the 5kW Vaillant no longer produces the required output. That is the gap that I think needs explaining.
Heat Geek may believe the calculated 6.4kW heat loss is substantially higher than the house will experience in reality, and they may have enough installation data to support that judgement. That is possible, but if the proposal states a 6.4kW heat loss at -3.6C, I think it is entirely reasonable to ask how the chosen heat pump and existing radiators meet it. The headache is getting stronger.
People/installers will also understandably point out that we only get a limited number of days at the design temperature. That is true, but those are precisely the days when the design really makes a difference IMO. Trust me, from experience, an extended cold spell is deeply unpleasant when the heat pump cannot replace the heat the house is losing. The temperature gradually slips, the heat pump runs relentlessly, defrosts and hot water cycles take more capacity away, and increasing the flow temperature in an attempt to catch up can cost a small fortune without necessarily restoring comfort. A fortnight of that in January feels considerably more important than its small percentage of the year suggests. Just speaking from experience having had a unit that couldn't deliver the required heat when we dropped below zero.
This is also where the guarantee’s fine print re-enters the picture. A good annual efficiency figure does not necessarily prove that every room will remain comfortable during the aforementioned coldest fortnight. I would want Heat Geek to confirm in writing that all the intended rooms will maintain their specified temperatures at -3.6C, including the effect of defrosting and hot water reheating, while still meeting the promised efficiency. I would also ask what happens if comfort can only be restored by increasing the flow temperature and that then pulls the annual efficiency below the guaranteed figure. The guarantee could still make this a very good consumer proposition, but it needs to guarantee both outcomes together... a warm house during the design conditions and the promised efficiency over the year. One should not be achieved at the expense of the other IMO.
If heat geek had mentioned that traditional calculation would have your house at 6.4kW heat loss but our 1000's of installs and algorithm estimates that actually your heat loss is close to 5kW and hence we are recommending the 5kW unit. Everyone else is going the traditional route and suggesting 7kW unit and we are suggesting 5kW for the above reasons. If for any reasons we have got it wrong you have our guarantee.
I wouldn't have questioned them at all if they had said the above.
Heat loss estimation is not simple to get right. But sizing once you have the heat loss estimate and design temp is relatively straightforward based on heat pump manufacturers spec.
In my case they have confirmed 6.4kW heat loss. I dont have any more info.
