What would you do?

[jayc89]

• ~1880s solid brick detached house. Approx 220sqm.
• 3m high ground floor ceilings (~2.4 first floor)
• 300mm rockwool in loft
• 1970s upvc windows, no trickle vents.
• Wet UFH downstairs mixer set to 35, but in reality the flow is more like 40. 100mm PIR below screed. Approx 420m total pipe length.
• Radiators upstairs
• Unvented Cylinder (set to 55c)
• 33kw gas system boiler set to 75c flow (for upstairs rads)
• Planning a two storey extension which will likely increase the footprint ~ 140sqm
  • Likely 175mm cavity (EPS beads)
  • Likely 200mm EPS below slab

 

The house never struggles to reach temp (i.e. 21c) but it never feels "toasty". No signs of damp (other than where the old cellar was), so I'm suspecting this is air leakage.

 

Over the past 12 months we've apparently used 31,000 kWh of gas and 4,000 kWh of electric. 

 

I've heard the saying "AIM before APE" which I'm trying to follow as near as reasonably possible.

 

Working on airtightness, the house was fully stripped, air bricks removed (when suspended floor was replaced with slab), holes were plugged when they were found, all walls are wet plastered. 

 

We don't want to install EWI and hide the lovely brick work and it's too late to install IWI to ~140sqm of the existing house. We plan to fit it to the remaining ~ 80sqm of the existing house as we extend.

 

When we extend we'll likely have a reasonable size south facing roof, perhaps 12x6m, so I'm really planning for what we should be using at that point. Ideally we'd reduce our reliance on gas, as our current usage is just crazy high. Perhaps some hybrid approach using an ASHP to power the UFH and maybe PV to feed the ASHP and/or heat the unvented cylinder, leaving the gas boiler for the upstairs rads and topping up the hot water when required.

 

What would you do?

 

[richi]

Are you timing the heating traditionally (i.e., off overnight and perhaps during the day)? Or are you keeping it on 24 hours "low and slow" (perhaps with a nighttime temperature setback)? 

[jayc89]

1 minute ago, richi said:

Are you timing the heating traditionally (i.e., off overnight and perhaps during the day)? Or are you keeping it on 24 hours "low and slow" (perhaps with a nighttime temperature setback)? 

 

Downstairs UFH is set to 21 throughout the day (6am - 9pm) and setback to 18 overnight.

 

Upstairs radiators are set to 21 from 6am to 9am and 4pm to 9pm (basically whilst the kids are awake and likely upstairs somewhere). The rest of the day it's set to 19.

 

The upstairs radiators are on constantly during those "peak" times, but the downstairs UFH rarely comes on at all during the day. I don't think I've ever seen either call for heat during the setback hours.

[richi]

I'll leave it to someone more knowledgeable to advise, but isn't 75 flow rather hot for a condensing gas boiler? Are you keeping an eye on the return temperature?

 

But then if your rads seem to be hot all the time, one has to wonder where all that heat is going. Time to walk around outside with a thermal camera? Shame it's not cold now.

[jayc89]

8 minutes ago, richi said:

I'll leave it to someone more knowledgeable to advise, but isn't 75 flow rather hot for a condensing gas boiler? Are you keeping an eye on the return temperature?

 

But then if your rads seem to be hot all the time, one has to wonder where all that heat is going. Time to walk around outside with a thermal camera? Shame it's not cold now.

 

Good point, I should have mentioned that. According to my, fairly basic, heat loss calc, it looks like our radiators were spec'd for delta t50 so with a flow rate any lower the rooms don't warm up suitably. I plan to spec my own for the extension, and they'd be overspec'd for something along the lines of t30 (I've not really put too much thought into that yet)

Edited March 24, 2022 by jayc89

[JohnMo]

You want your CH return temp below 54 degrees.  The lower from there the better.  It is worth something like a 10 to 20% cut in your heating bill.  We are assuming your boiler isn't as old as the hills and is condensing?  Your flue should burn clean with very little or no white smoke coming out, if you are in condensing mode.

 

As mentioned low and slow.  Your heating system is designed for the coldest day, so any day or time warmer than that, it should be having an easy time.

 

You would be better turning you CH temp down to 60 (supply temp) and running the upstairs rads for longer.  Does you boiler have weather compensation?  You may be better moving to that if you have it or can add it.  This changes the CH flow temp based on outside temp.  It runs all the time and uses the low and slow principle.

 

Also do you need the heating at 21, 1 degree less will save a big chunk as well.

[jayc89]

37 minutes ago, JohnMo said:

You want your CH return temp below 54 degrees.  The lower from there the better.  It is worth something like a 10 to 20% cut in your heating bill.  We are assuming your boiler isn't as old as the hills and is condensing?  Your flue should burn clean with very little or no white smoke coming out, if you are in condensing mode.

 

As mentioned low and slow.  Your heating system is designed for the coldest day, so any day or time warmer than that, it should be having an easy time.

 

You would be better turning you CH temp down to 60 (supply temp) and running the upstairs rads for longer.  Does you boiler have weather compensation?  You may be better moving to that if you have it or can add it.  This changes the CH flow temp based on outside temp.  It runs all the time and uses the low and slow principle.

 

Also do you need the heating at 21, 1 degree less will save a big chunk as well.

 

It's a 33kw Baxi Platinum+. It's certainly a condensing boiler but I'm led to believe it's not the most efficient out there.

 

21c is where the family feel most comfortable. I certainly want to make changes to reduce our energy usage but I'm not sure dropping the temp will fly with the boss

[Radian]

42 minutes ago, JohnMo said:

You would be better turning you CH temp down to 60 (supply temp)

 

There's a potential issue with DHW at this lower temperature. The cylinder stat should be set around this figure (for anti legionella) and the boiler might just run constantly while trying to reach it.

[jayc89]

DWH is set to 55c, I'd suspect 60c + lagged pipes would work?

[JohnMo]

Do you need anti legionella in the UK?  The supply water coming in to your house is chlorine treated to kill everything.

 

About previous comments ref weather compensation, this cannot be done with this boiler, as far as I can see.

 

 

[jayc89]

2 minutes ago, JohnMo said:

Do you need anti legionella in the UK?  The supply water coming in to your house is chlorine treated to kill everything.

 

About previous comments ref weather compensation, this cannot be done with this boiler, as far as I can see.

 

 

Re: weather comp. That's my understanding too. I wish I came across this site sooner

I've spent the afternoon ensuring the rads are balanced and dropped the flow to 65. I have a couple of clip on thermometers so I've attached one to the return pipe going back into the boiler. It's a pretty nice day here so heating's not flicked on yet (and I doubt it will) so I'll check back on it when it does.

[JohnMo]

Site worth a read.  Lots of info on getting best from your system

 

https://www.heatgeek.com/category/knowledge/balancing/

[Conor]

Keep it simple. Keep boiler, PV on roof to offset your day to day usage and a solar diverter to heat your UVC during the sunny days.  Go to town on your extension air tightness and insualtion  (200mm full fill cavities, 150mm PIR in floor or 300mm EPS, basically passive standards) so your minimising the additional heat load of the building replace your crappy double glazing with decent triple.

Edited March 24, 2022 by Conor