Heating System Basics...

[Mulberry View]

As we begin to consider design for our new self-build, I'm keen to learn what the current go-to is for heating/hot water etc.

 

We've been dogged for years by a home that, whilst very beautiful, has a condensation problem and we're sick of it. So we want to ensure our new home is totally free of that.

 

So, Ground Source/Air Source/Other? The plot is big, so I think that makes Ground Source a possibility? I guess this is best used with Underfloor heating? I like a simplistic look, so that would be my preference.

 

I'm assuming an MVHR system will deal with the condensation side of things? Is that the gold standard? Does the MVHR system provide any meaningful heat to the home?

 

What about the hot water? I'd like a system that finds a good medium between responsiveness and cost. In our current home, we have a hefty D-rated non-condensing boiler, which, whilst it delivers great hot water performance, does see us waiting upwards of a minute to get hot water to our bathroom basin and I'm sure it's probably answerable for out £100+ monthly gas bills over the Winter months.

We were also early PV adopters, so we're on the mega tariff (circa 50p/kwh), which we'll of course be leaving behind when we sell our current home. I know PV is nowhere near as lucrative as it was back then, but is it still worth considering?

 

As usual, your help is absolutely invaluable and appreciated as we get to grips with this...

[ProDave]

The key to a condensation free house is insulation and lots of it.  I am willing to bet your old house has very little insulation hence cold wall surfaces where moisture condenses and mould forms.

 

If you build with a decent insulation level then the next thing is make it air tight and coupled with that an MVHR ventilation system

 

That will give you a warm house free from condensation with low heating requirements.  Which lends itself to heating by under floor heating at low temperature from a heat pump.  There is no doubt a ground source heat pump is slighthy more eficcient than an air source, but when you properly cost it, there are a lot of additional costs and ongoing maintenance costs.  Most of us who have looked into it decided the sheer simplicity of an air source heat pump wins hands down.

 

An ASHP will do domestic hot water, I have a 300 litre tank. The key is you store your hot water less hot that you would with a gas boiler. Ours is set to 48 degrees which is plenty hot enough, but the lower temperature points you towards a larger tank.

 

And hot water distribution and careful pipework is the key to quick delivery to the taps.  Also some logical thought to the layout so all hot water usage points are close together, and the hot water tank central between them.

 

Lastly solar PV.  The FIT has gone, so anything now has to be self financing. That probably means forget paying an installer to fit it.  I installed my own earlier this year for a cost of £1500 and we are on target to self use £250 of electricity in the first year giving a payback time of 6 years.  Our generation is lower than it should be due to shading from trees, which I am gradually addressing with a thinning / felling program so I hope that will increase over time as I gradually reduce the shading.  You need a different mindset for near 100% self usage like use all big appliances one at a time in the middle of the day, and a solar PV dump controller to put surplus power into hot water is a must.

[Mulberry View]

5 minutes ago, ProDave said:

The key to a condensation free house is insulation and lots of it.  I am willing to bet your old house has very little insulation hence cold wall surfaces where moisture condenses and mould forms.

 

If you build with a decent insulation level then the next thing is make it air tight and coupled with that an MVHR ventilation system

 

That will give you a warm house free from condensation with low heating requirements.  Which lends itself to heating by under floor heating at low temperature from a heat pump.  There is no doubt a ground source heat pump is slighthy more eficcient than an air source, but when you properly cost it, there are a lot of additional costs and ongoing maintenance costs.  Most of us who have looked into it decided the sheer simplicity of an air source heat pump wins hands down.

 

An ASHP will do domestic hot water, I have a 300 litre tank. The key is you store your hot water less hot that you would with a gas boiler. Ours is set to 48 degrees which is plenty hot enough, but the lower temperature points you towards a larger tank.

 

And hot water distribution and careful pipework is the key to quick delivery to the taps.  Also some logical thought to the layout so all hot water usage points are close together, and the hot water tank central between them.

 

Thanks so much for that reply.

 

You're right about the shortfalls in our current property. It was built in the 1920's, we had cavity wall insulation installed a few years back, but I'm dubious of it's coverage and effectiveness. I also dropped a major design blunder with the hot water circuit. I've learnt from my mistakes though!

 

 

[PeterW]

A lot of your issues will be dependent on your design - do you have a fixed shape (planning granted..?) so you’re trying to retrofit all of the M&E, or have you got a blank sheet of paper ..?

 

Plan in the plant space carefully - big tanks need reasonable spaces around them, but you also need to make them as central as possible to get the shortest runs of pipe work. 
 

As @ProDave said - you need to focus on installation and air tightness, and then look at your heating requirements. It’s highly unlikely you can make a GSHP pay - they have a 2-3 times capital cost and a continued maintenance that will dwarf running an ASHP. You will need and ASHP of 5-8kW I would expect for both heat and hot water for a decent spec new build using UFH. 
 

10 hours ago, christianbeccy said:

Does the MVHR system provide any meaningful heat to the home?

That depends on the MVHR - if like @PeterStarck or @JSHarris you fit a Genvex with a small internal heat pump then it will provide a small amount of heat. The real benefit is that you don’t lose all the heat from the continuous air changes of the building, retaining  80-90% based on the unit you choose. 

[Mulberry View]

2 minutes ago, PeterW said:

A lot of your issues will be dependent on your design - do you have a fixed shape (planning granted..?) so you’re trying to retrofit all of the M&E, or have you got a blank sheet of paper ..?

 

Plan in the plant space carefully - big tanks need reasonable spaces around them, but you also need to make them as central as possible to get the shortest runs of pipe work. 
 

As @ProDave said - you need to focus on installation and air tightness, and then look at your heating requirements. It’s highly unlikely you can make a GSHP pay - they have a 2-3 times capital cost and a continued maintenance that will dwarf running an ASHP. You will need and ASHP of 5-8kW I would expect for both heat and hot water for a decent spec new build using UFH. 
 

That depends on the MVHR - if like @PeterStarck or @JSHarris you fit a Genvex with a small internal heat pump then it will provide a small amount of heat. The real benefit is that you don’t lose all the heat from the continuous air changes of the building, retaining  80-90% based on the unit you choose. 

 

We're at 'blank sheet of paper' stage. I'm certain, once we select an architect, this will all start to fall into place, but it's good for me to start the cogs turning.

 

Thanks for your input.

[ProDave]

I am not necessarilly sure an architect is the best person to trust with siting the plant and planning the pipework runs.  Once you have some initial plans post them on the forum and plenty of people will be able to suggest improvements.

 

As above, MVHR is mostly about stopping / reducing heat waste rather than it being a heat source.  You have to ventilate a house to provide fresh air to breath. Traditional uncontrolled trickle ventilation wastes the heat from all the expelled air and often does not ventilate properly (adding to mould problems)  MVHR gives you a controlled rate of ventilation with most of the heat from the expelled air recovered and put back into the incoming air.

[joe90]

I endorse all that’s said above, our last house was badly insulated, condensation and boiler running all the time. Our new build of 240 sq meters (in an exposed location) has a 4kW air source heat pump that I installed myself and apart from DHW it has not come on once yet this year. (We do have a wood stove which we had lit for a couple of evenings recently, more fir the  asthetics on a dark, wet evening) and our house temp is a steady 20-21 ‘. Last years running costs (house was still drying out) was at least half of the previous house and it was a semi, the new build is detatched, and with our planned going E7 hope to reduce it more.

[SteamyTea]

Heating is all about sizing correctly.  The lower temperature that is used by an ASHP is really a diversion, try putting your hand in water at 48°C and you will see what I mean.

First thing you need to do is calculate your heat load.  This is a relatively simple calculation, it just involved knowing (or making some assumptions) the U-Values (W.m^-2.K^-1) the area of each external wall, window and door, plus the floor and roof, and the expected external temperatures (from the Met Office for your area).

Then you can, for any desired internal temperature, calculate the heat loss. This will set the maximum losses, which is the same as the maximum load your heating system needs to deliver.

From that you can then, depending on your  choice of heating system i.e. GSHP, ASHP, Gas, Storage Heaters... go looking for suitable emitters (radiators, forced air, UFH).

 

Domestic Hot Water (DHW) is pretty simple.  Just a case of working out how much water you need, then the energy needed to heat it up.  You probably have this information already a you own a hows with bills.  Moving house does not change the amount of hot water that is used, generally.

[ykhan16]

Hi @christianbeccy we're actually in a similar position as you -just starting out and considering designs, heating options and finding an architect.

 

I was quite keen on ground source pumps at first and then air source but now i'm re-evaluating them. I'm not really sure what your priorities are but i'm looking for the best value system so I can have UFH in the home and its cosy throughout as well as, importantly, bathrooms staying dry (kids always leaving puddles around atm grrr ). I've kind of concluded that air-source is better than ground source, but its actually not that cheap to run even taking RHI into account. 

 

Atm i'm drifting towards solar heating for the hot water (no running costs, low maintenance + RHI) and maybe with a small boiler. Underfloor heating i'm now thinking along the lines of Infrared mats which are electric but very energy efficient, zone-able and also healthier (apparently!).

[ProDave]

10 minutes ago, ykhan16 said:

..... I've kind of concluded that air-source is better than ground source, but its actually not that cheap to run even taking RHI into account. 

 

Atm i'm drifting towards solar heating for the hot water (no running costs, low maintenance + RHI) and maybe with a small boiler. Underfloor heating i'm now thinking along the lines of Infrared mats which are electric but very energy efficient, zone-able and also healthier (apparently!).

Where do you derive that statement from?

 

Taking into account the COP of a heat pump, the actual running cost per KWh of delivered heat is comparable to mains gas price, making it a very viable option when you don't have access to gas, and saving an additional install cost and standing charge if you do.

 

Solar thermal does not have zero running cost and has a maintenance cost.  Yes it can work very well, but not as your only hot water heating (it would be useless today)

 

Electric resistance IR heating is 100% efficient like any other form of electric heating compared to a heat pump that will be between 300 and 400% eficcient by the same measure.

 

Be careful not to be taken in by some outrageous claims by some systems.

[Jeremy Harris]

Pretty easy to do some basic running cost comparisons for different fuels.

 

Just comparing cost per kWh of heat delivered (so allowing for boiler efficiency, heat pump COP, etc), then these are the approximate heating costs,  excluding standing charges or tank rental (for all-electric heating this should really be apportioned across all electricity consumption, as it will be paid anyway):

 

 

Peak rate electric boiler running UFH = £0.15726/kWh

 

LPG fired boiler running UFH = £0.08471/kWh

 

Off peak (E7) electric boiler running UFH = £0.08148/kWh

 

Oil fired boiler running UFH = £0.07647/kWh

 

ASHP at peak peak rate running UFH = £0.05242/kWh

 

Mains gas boiler running UFH = £0.04274/kWh

 

ASHP at off-peak (E7) rate running UFH = £0.02716/kWh

 

For all the above the ASHP was assumed to be running with a COP of 3.  In reality, ours seems to run at a COP of ~3.5, so a bit better than these figures suggest.  The electricity cost figures above are for our E7 rate, so may well be different in other areas/for other tariffs.

 

Edited November 3, 2019 by Jeremy Harris
Error in LPG cost corrected

[MikeSharp01]

You have almost all the guidance you need on the heating system above, just the Sunamp or similar (not much) option to look at, but the Architect is another matter. We provacated a lot about our long list of architects. We wanted a passive house standard of build - loads of insulation, 3G Windows, very good air tightness etc. The problem we had was that all the PH experianced architects seemed to be designibg with a limited pallet and we wanted a modest home that makes a statement. l felt I could handle the energy calcs, I went on a PHPP training course, and that allowed us to engage an architect who had not done a PH before but who was prepared to let me be the PH consultant as it were. We are nowhere near finished but I am confident we have a great standout design that will meet the PH standard.

[ykhan16]

1 hour ago, ProDave said:

Where do you derive that statement from?

 

Taking into account the COP of a heat pump, the actual running cost per KWh of delivered heat is comparable to mains gas price, making it a very viable option when you don't have access to gas, and saving an additional install cost and standing charge if you do.

 

Solar thermal does not have zero running cost and has a maintenance cost.  Yes it can work very well, but not as your only hot water heating (it would be useless today)

 

Electric resistance IR heating is 100% efficient like any other form of electric heating compared to a heat pump that will be between 300 and 400% eficcient by the same measure.

 

Be careful not to be taken in by some outrageous claims by some systems.

 

Not that cheap in comparison to a gas/boiler system is what I meant. IR system looks interesting to me given that it heats solid matter as opposed to air etc so effective efficiency should in theory be higher.  I'll need to price it up and do some calculations but you are right and I need look at it objectively!

[ProDave]

2 minutes ago, ykhan16 said:

 

Not that cheap in comparison to a gas/boiler system is what I meant. IR system looks interesting to me given that it heats solid matter as opposed to air etc so effective efficiency should in theory be higher.  I'll need to price it up and do some calculations but you are right and I need look at it objectively!

These IR systems were discussed recently.

 

If you have an old leaky building with high heat loss, they might have some merits. They work well in a church for instance where all you want to do is heat the congregation for an hour a couple of times a week, not keep the whole fabric of the building warm all the time.  But in a modern well insulated house you simply won't avoid the whole house heating to the same temperature, and then they are no different to any other form or resistance electric heating.

[Jeremy Harris]

Yes, over a period of a few hours the IR system will be exactly the same as any other heating system.  Over time, all the stuff inside the house gets up to temperature, and from then on the heat energy input, for any heating system, will just equal the heat losses, less the incidental heat gain from the occupants, appliances etc.  The latter can be very significant for a well insulated house with decent airtightness and MVHR.  For quite a lot of winter days two occupants plus a couple of hundred watts of heat from appliances etc is enough to keep our house comfortably warm, with no heating needed.

[SteamyTea]

5 hours ago, ykhan16 said:

given that it heats solid matter as opposed to air

We are in contact with the air, and we breath it in.  Can't say the same for my floor, or walls.

[ykhan16]

6 hours ago, ProDave said:

These IR systems were discussed recently.

 

 

Thanks @ProDave I will try to dig this up!

[ProDave]

8 hours ago, ykhan16 said:

 

Thanks @ProDave I will try to dig this up!

I think it was this thread 

 

[TerryE]

Dave, that last figure that you referenced is really misleading for a passive house: surface temperatures of 15°C are just silly, IMO.    All of the internal surfaces, ceilings, etc will be at equilibrium with the air temperature and even the external walls will be reasonably close: the rough guide is 7W/°C radiant transfer to a surface, so with a U-value of 0.12, say and a delta T of 17°C (and few places in the UK have greater than this as daily average for more than perhaps 30 days a year), then the net heat flow through the external wall will be maybe ~2 W/M² which will make the external walls less than ½°C cooler.   

 

In our case the only surface that is materially different is the slab which might get a couple of degrees warmer when the UFH is on.  I've gone around our house with an IR thermometer and its readings are consistent.  The external corners are perhaps ½°C cooler.  The big delta is in the window reveals where the 10cm closest to the outside might be 2-3°C cooler, but everything else is basically at the same temperature  ±¼°C. 

 

We only have heating on the ground-floor slab, so the 1st floor is heated parasitically and the similar distribution exists but maybe a degree cooler.

 

So my advice to any new builder is not to over-engineer the heating solution and just concentrate on getting the walls (as built) to a maximum U-value of 0.14, say, get it decently airtight and invest in an MVHR and decent triple-glazed fenestration.  If you do this, then you will have a warm house in winter and (so long as your architect hasn't persuaded you to have acres of south facing glass) a cool house in the summer.

[ykhan16]

@TerryE That sounds sensible. Can you confirm you didnt put UFH in your upstairs bathroom? My upstairs will be carpeted but will tile the bathroom and ensuite so would worry about them being cold to feet and slower drying. Many thanks!

[Jeremy Harris]

FWIW, we only have UFH on the ground floor, and no heating at all in the bedrooms, but we find that the bedroom temperatures are, if anything, a bit too warm at times, just from heat that rises from the warmer ground floor.  With regard to bathrooms, then one thing I wish I had done was fit UFH in ours.  The bathroom temperature is fine, no need for any heating really, but having the floor slightly warmed would be nice.  I'd not bother to fit wet UFH in the bathrooms, as I think that just fitting low power electric heating mats under the flooring would be fine.  They would be cheaper and easier to install, and the running cost would be low, as the need for a bit of heat in the floor is only really for a very short time each day.

[epsilonGreedy]

22 hours ago, Jeremy Harris said:

LPG fired boiler running UFH = £0.16471/kWh

 

 

The LPG cost looks odd, how is this figure derived?

 

Many other references online indicte the cost is half that.

 

https://www.energysavingtrust.org.uk/about-us/our-calculations

 

https://nottenergy.com/resources/energy-cost-comparison/

 

https://www.which.co.uk/reviews/home-heating-systems/article/home-heating-systems/lpg-central-heating

 

https://www.thegreenage.co.uk/cheaper-heat-home-gas-electricity/

 

 

[Jeremy Harris]

17 minutes ago, epsilonGreedy said:

 

The LPG cost looks odd, how is this figure derived?

 

Many other references online indicte the cost is half that.

 

https://www.energysavingtrust.org.uk/about-us/our-calculations

 

https://nottenergy.com/resources/energy-cost-comparison/

 

https://www.which.co.uk/reviews/home-heating-systems/article/home-heating-systems/lpg-central-heating

 

https://www.thegreenage.co.uk/cheaper-heat-home-gas-electricity/

 

 

 

 

Looks like I made an error and used the wrong price for LPG.  I'll edit that table to fix the error.  Not sure what happened, but it looks like I may have read off the cost for low volume LPG, rather than bulk LPG.

[epsilonGreedy]

6 minutes ago, Jeremy Harris said:

but it looks like I may have read off the cost for low volume LPG, rather than bulk LPG.

 

 

That would be it, bottled LPG prices are silly. I am currently paying £58 for a 47kg bottle to keep the static caravan warm or about £0.60 per litre.

[PeterW]

Just now, epsilonGreedy said:

 

That would be it, bottled LPG prices are silly. I am currently paying £58 for a 47kg bottle to keep the static caravan warm or about £0.60 per litre.

What’s the current bulk prices now ..? I saw Calor do their usual pre-cold snap hike a couple of weeks ago.