With you there @toodles, I too have noticed the even house temperature into every corner from the barely warm large rads that we retro fitted when installing the HP. Happy customers here.

It is not just with heat pumps, it is how the system is controlled.

We still have an old gas boiler, but the way it is controlled means that the average temperature of the radiators is modified to maintain a fairly consistent 21C IAT. The temperature of the radiators is varied between probably 25C and 45C as the heating demand changes with OAT.

@derek-m Yes, this is what I mean, the lower temperature (rather than ~65-70 degrees as some older systems might be set to run) removes the fierce heat that rapidly drops off over a short distance. Regards, Toodles.

Definitely - rooms feel uniformly comfortable as opposed to noticeably warm with bands of “hot” air at head level from higher flow temperatures.

@derek-m Our gas boiler (thankfully gone to boiler heaven or re-cycling plant) did feature condensing in the design but… there was only one temperature control and this catered for DHW as well as the heating. I could not run the heating at a lower temperature for fear of problems with the risk of legionella in the DHW circuit. Things were not helped by the boiler [installed by BG] being on the default setting of 18 kW unbeknownst to us when a much lower setting would have sufficed. Regards, Toodles.

@toodles

I'm still running my gas boiler while I attempt to characterise the thermal properties of my property.  I've range rated the boiler as low as it will go and reduced the flow temperature to just under 70degC (I'm logging flow and return temperatures). I leave it on 24hours/day. It's a simple condensing boiler with its only apparent control sensor being the flow temperature thermistor; I can't detect any burner modulation other than the on/off operation of the gas valve. I can't understand what its system control parameters are, unless there is some 'predictive' element. In the absence of any other effective control, I have retained the room thermostat (there are TRVs, too). The room thermostat provides the boiler modulation, cycling the boiler every 10 minutes or so.  It is interesting to see the average flow temperatures slowly varying throughout the day and doing an amazing job of maintaining a constant, even ambient temperature (it would be even better if the radiators were balanced). Even during the sub-zero cold snap in the middle of January, the boiler managed to meet heat demand while still cycling off occasionally as the flow temperature hit the 70gegC set point.

Incidentally, I have been on the Octopus Gas Tracker tariff this heating season and I have to say that the financial calculations for an ASHP versus a new boiler will make for a more difficult decision until such time as the carbon taxes are redistributed.

Yes.

Simple as that, much more comfortable due to reduced temperature gradients both in temperature and time.  The only question is, why has it taken so long to wake up to this simple realisation?

Posted by: @jamespa

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Yes.

Simple as that, much more comfortable due to reduced temperature gradients both in temperature and time.  The only question is, why has it taken so long to wake up to this simple realisation?

It is not so much waking up to the fact, as improved methods of control. The old bi-metal thermostats probably had a switching differential of 1C at best, so would switch the boiler on when IAT fell to say 20C, the boiler then continuing to operate until the IAT reached 21C. During colder weather IAT would probably fall below 20C as thermal energy eventually heated initially the heat emitters and then the indoor air and eventually the fabric of the building. In milder weather conditions the IAT would increase above 21C as the hot heat emitters continued to supply thermal energy after the boiler has shutdown.

I suspect that many homeowners were not aware of how to operate their boilers in condensing mode, why should they, the boiler worked and kept their home warm at reasonable cost. The 'experts' had installed their boiler and set it up for 'efficient' operation.

@toodles First winter with ASHP, replaced old condensing gas boiler. Runs 24/7 and although radiators are running at lower temperature than with gas boiler, the house is always more comfortable than before.  Despite research suggesting that this would be the case, it still surprised me.  So far cost of energy is meeting expectations as well.

@ianmk13 It is a right bummer that the ‘dirty’ fuel is the cheaper isn’t it? Now, if I was running the country …

Regards, Toodles.

@jamespa  I imagine that the hysteresis of a mechanical thermostat would work against maintaining a comfortable stable temperature. I presently have a Drayton miGenie controller (shortly about to lose its 'Cloud' connection due to being an 'obsolete' product) and the on/off duty cycle of the boiler seems to be updated every 10 minutes or so - I worry about resultant wear on the gas valve (IIRC there is a setting deep in the menus for oil or gas heating which I believe comes into play here).

@noburn I experience the same, with radiator temperatures often being warm rather than hot as OAT decreases. Although the average flow and return temperatures rise and fall, the deltaT is fairly constant.

My property is two storey and split-level.  The upstairs corridor can become a little too warm overnight as the downstairs kitchen/diner and lounge both have large expanses of glass.  I intend to extend my temperature monitoring to these rooms to see if I can improve on the theoretical heat loss values. The downstairs radiators are all fed via 10mm microbore from 15mm pipes in the ceiling.  This may or may not be a problem although the two large column radiators in the kitchen diner may be insufficient if I move to a lower flow temperature system.  I may have to find wall space for a 3rd matching radiator.