I’ve had a quotation for a heat pump install and in that quote was a Vaillant aroTHERM plus 3.5kW - VWL 35/6 - 3.5kW Heat Pump, I know very little about this brand or heat pumps. How do they stack up against other brands ?
Dave.
Dave,
Take a look at this site → Best Air Source Heat Pump Manufacturers | Boiler Guide
Not all the manufacturers are on there. You can click through for more detail but it’s pretty high level. It’s not easy to get good comparisons between the manufacturers - I’ve been looking for this for a while.
There’s a lot of discussion on the various types etc. on the self build forum → https://forum.buildhub.org.uk/. Lots of experience there with various types (monobloc or split, GS and AS etc.) and the different manufacturers.
Simon
Thanks Simon,
The pdf of the heatpump is https://www.vaillant.co.uk/downloads/aproducts/renewables-1/arotherm-plus/arotherm-plus-spec-sheet-1892564.pdf
We currently have oil with a 25kw combi boiler the bungalow is round 75m2
Dave.
Hopefully they aren’t suggesting the 3.5kW ASHP as a replacement for the combi - unless you like things just above the outside ambient temperature. Or have you done a massive amount of insulating?
Simon
Simon
Another useful site for anyone thinking of installing a heat pump is the BRE site where you can compare the relative efficiencies of different heat pumps.
https://www.bregroup.com/heatpumpefficiency/index.jsp
Simon
Er yes, I asked them to give a quote for a heatpump to replace the oil combi boiler, insulation is so-so 250mm in the loft, cavity filled walls which has sagged I think - it looked like fluffy spider webs beige’ish in colour, old double glazing and solid floor. We’re in West Cornwall …
The quote includes heat loss calculation which is 10463 kWh therefore, a 3.5kw heatpump would appear ok 
(The BRE link seems to have similar results)
Hi Dave,
Our heat loss analysis gave us 2 numbers one for the annual heat requirement (~16500kWhs in our case) and another for the peak demand at an outside temperature of -2C which was ~6kWhs. It’s a highly insulated new build of about 250sq.ms. The heat loss analysis doesn’t take into account any heat from appliances or the inhabitants, or solar gain, so might be lower. On the other hand it doesn’t take into account the additional requirement for DHW, so would be higher, I’ve calculated we’d need ~3.3kWhs/day when we’re not getting any input from solar PV.
I’ve read that you should size the heat pump at 30% higher than the DHW heating requirement for a sensible reheat time. A 200l tank would require 10kWhs to reheat from 10C to 50C. So for a reheat time of 2 hours, this implies an ASHP with about 6.5kW capacity. Would be interesting to ask your contacts what the reheat time would be with the 3.5kW ASHP they are proposing. The AroTherm does have a 6kW instantaneous heater I think which obviously would be used if the ASHP hasn’t managed to reheat the tank - but that would be 3x as expensive as waiting for the ASHP to do it’s job.
We’ve got a call with the firm that did the heat loss analysis to discuss our conclusions on Wednesday - I’ll report back if our numbers don’t add up.
Simon
Thanks Simon,
That’s really interesting, going by very simplistic numbers our bungalow is around 0.3 of the area of your house and a heat pump of 3.5kW would seem to be adequate. With only two of us in the house our hot water use is very minimal, we also have an 8.5kW electric shower (I know).
I currently use the combi boiler in a slightly unconventional way, what I mean I have it come on for 20 Minutes in the morning to heat hot water and again for 20 mins at 13:00 both for washing up breakfast and lunch (main meal at 13:00) the rest of the the time the 69L ‘heatstore’ in the external boiler stores enough heat for hand washing. Heating, I have come on 20mins in the morning and again in the evening 19:30-20:30. The 1 hour heat button gets pressed when it feels cold ! Being in the far sound west it’s very damp and we do suffer from condensation on the bottoms of the external walls - mainly caused through varying temperature and probably a lack of ventilation. As with a lot of houses in Cornwall we do use a dehumidifier.
Our annual oil use is 683L or ~7034 kWh into the boiler (it’s strange that out last two fills have been identical amounts of 683L!)
Forgot again to add the two figures for heat loss, total power heat loss of 3.93kW and an annual space heating and water demand of 10,463kWh from before.
Dave.
Here’s a couple of pages from the quote …
Hi, I’ve been i contact with my proposed installer of an heat pump and they could also supply Mitsubishi heat pumps or the Vaillant. Anyone know which would be the better option ?
Dave.
Thanks everyone, But I’m thinking against having an heat pump installed because of the additional £4K for larger radiators (that might be needed) to be installed.
Dave.