Building extension, are we missing a trick to future proofing energy

Section62

thebizz said:

To move to a heatpump in say 10 years, what do you think we could do to prepare for it?  

I'd say (as a minimum) -

1) Identify and retain a space in the house where you could put hot water storage, ideally as close as possible to the most frequently used tap, or a compromise position if two distant taps are used frequently.

2) Identify and retain a space in the house where the internal unit (if any) of a heat pump would be located.

3) If the house is being reqired, consider running a suitably sized feed from the consumer unit to 2.

4) Any replacement radiators/pipework should be sized for the lower circulation temperatures used with heat pumps.

The point about 1 is you probably already have it in the form of the space where the hot water cylinder is currently located.

thebizz said:

There doesn't seem to be any love for combi boilers?

There is some love for them, but gas prices are going up and those with foresight can see a time coming where the availability of replacement gas boilers will be extremely limited.  The industry is in a state of flux, and the only thing which appears certain is the future - whatever else it holds - will almost certainly mean the most economic forms of heating will involve some degree of storage.

Hot water cylinders are a form of energy storage.  They have been around for decades and are proven technology.  Getting rid of one and replacing it with a gas combi boiler isn't the most obvious solution now, unless there were other factors involved. Because you are extending the property, the most obvious one (lack of space) shouldn't apply in your case.

A hot water cylinder enables the storage of energy either from PV solar (via an immersion heater) or from the output of a heat pump.  Unlike a combi, a heat pump can't efficiently heat hot water on demand, hence the need to store heated water for when it is required.

thebizz said:

If we got a tank in the bungalow then we would need to get an unvented one.

Could you explain this a bit more?  Lots of bungalows have vented hot water systems.  Is there a specific reason why you think you need to go unvented, or is it just that someone has told you to do so?

thebizz

FreeBear said:

thebizz said: To move to a heatpump in say 10 years, what do you think we could do to prepare for it?  
Good advice regards the insulation.  We will be working with the builders and window fitters to make sure no corners are cut.

As other posters have mentioned, oversize the radiators so that they can heat each room with a lower water temperature - Radiators are often sized based on a CH water temperature of 70°C and a room temperature of 20°C and quoted in the specs as either Δt=50 or deltaT=50. For a heat pump, you should be looking at radiators using a Δt=30 or lower. This generally means increasing the size of the radiator by 25% or even 50% (or fitting two instead of just one). The alternative is underfloor heating, but this really needs to be installed during construction and not as an afterthought.

Even if you don't fit a heat pump today, having oversized radiators means that you can run the existing (condensing ?) or new combi boiler at a lower temperature which should enable it to run at a higher efficiency.

Don't forget, a heat pump will (usually) require a hot water tank, so if you like hot showers, you should consider having an electric shower installed.

Thanks, we were going for 25% plus for all the radiators.  The existing part of the house already has radiators that are about 50% larger than required so thats good.
I had thought about electric showers but I am put off by the experience when staying at other peoples houses when they seem pretty underwhelming.  I am generally quite thrifty but a good shower is one of the last things I would want to cut back on.   I guess it's just a case of having adequate shower kw to equal the flow and heat of a combi/tank?

matelodave

Perhaps you really need to sit down and plan what you've got, what you want, how you want to use it and what might happen in the future.

Are you trying to work around what you've got and add stuff to it in a random fashion or are you trying to futureproof the place. If its future proofing then make sure you think it through properly coz it may not be everso easy to add or shift stuff in the future and do you really want to spend money twice, now and in the future or spend a bit more now so you dont have to spend it all again a few years down the line.

We did a refurb 12 years ago to our 140m2 bungalow and went for a heatpump with undefloor heating and a hot water cylinder (unvented). Its proving to be reliable and cheapish to run (probably not as cheap as gas though but we dont have gas where we live). If push comes to shove, replacing it would be a simple matter of pulling out the old one and fitting a replacement in its rather than having to replumb the place.

If you are sticking with radiators then make sure that they are capable of heating the place with low flow temperatures as that will help improve your running costs even with a gas boiler and you'll have the option of replacing the boiler with a heatpump. Look at where you are going to install a boiler or tank so that it will be easy to replace it with something else in the future without re-running plumbing all over the place. TBH it not difficult to install a boiler or hot water in the loft against a gable wall if you are stuffed for space in the kitchen or utility room.

A monobloc heatpump has all it's gubbins outside so you only need to find space outside to site it and some space indoors for a hotwater tank.

thebizz

Section62 said:

thebizz said:

To move to a heatpump in say 10 years, what do you think we could do to prepare for it?  

I'd say (as a minimum) -

1) Identify and retain a space in the house where you could put hot water storage, ideally as close as possible to the most frequently used tap, or a compromise position if two distant taps are used frequently.

2) Identify and retain a space in the house where the internal unit (if any) of a heat pump would be located.

3) If the house is being reqired, consider running a suitably sized feed from the consumer unit to 2.

4) Any replacement radiators/pipework should be sized for the lower circulation temperatures used with heat pumps.

The point about 1 is you probably already have it in the form of the space where the hot water cylinder is currently located.

thebizz said:

There doesn't seem to be any love for combi boilers?

There is some love for them, but gas prices are going up and those with foresight can see a time coming where the availability of replacement gas boilers will be extremely limited.  The industry is in a state of flux, and the only thing which appears certain is the future - whatever else it holds - will almost certainly mean the most economic forms of heating will involve some degree of storage.

Hot water cylinders are a form of energy storage.  They have been around for decades and are proven technology.  Getting rid of one and replacing it with a gas combi boiler isn't the most obvious solution now, unless there were other factors involved. Because you are extending the property, the most obvious one (lack of space) shouldn't apply in your case.

A hot water cylinder enables the storage of energy either from PV solar (via an immersion heater) or from the output of a heat pump.  Unlike a combi, a heat pump can't efficiently heat hot water on demand, hence the need to store heated water for when it is required.

thebizz said:

If we got a tank in the bungalow then we would need to get an unvented one.

Could you explain this a bit more?  Lots of bungalows have vented hot water systems.  Is there a specific reason why you think you need to go unvented, or is it just that someone has told you to do so?

Currently its a bungalow.  The whole back loft space will be converted into a dormer.  There will still be a reduced height loft space over a front bedroom earmarked for storage.  a  Currently, there is gravity-fed water feed tank in the loft.  The tank is calcified and is scrap anyway.  That whole space will be a bedroom with some amazing views.   The boiler is a Greenstar 15 which is rated for 10 radiators and we will need 11 radiators minimum (about 140m2).  We actually dont use that much heating and at least 3 of the radiators will be on tickover with the doors closed most of the time as are just spare bedrooms/2nd office. The boiler is in a detached garage 1 meter away from the house.  So the heat from the boiler itself goes into the garage and then the hot water travels back to the house externally in a brick arch with pretty minimal insulation.
When we spoke to the plumber (briefly a while ago) he suggested a combi in the utility room or he could fit an unvented cylinder either in the garage next to boiler or sideways on in the low areas of the loft. Not sure if building regs or the plumber need to sign off the capacity of the boiler.  It was only fitted 2 years ago just before we bought the house so a shame to waste it but I think it will be underpowered.
From a cost-saving point of view, we are pretty economical and have always had a jumper-first policy, and our combined elec/gas bill for a 1990 5 bed being around 1k per year up to this year when obviously it has gone up a lot.

Mstty

FreeBear said:

thebizz said: To move to a heatpump in say 10 years, what do you think we could do to prepare for it?  
Good advice regards the insulation.  We will be working with the builders and window fitters to make sure no corners are cut.

As other posters have mentioned, oversize the radiators so that they can heat each room with a lower water temperature - Radiators are often sized based on a CH water temperature of 70°C and a room temperature of 20°C and quoted in the specs as either Δt=50 or deltaT=50. For a heat pump, you should be looking at radiators using a Δt=30 or lower. This generally means increasing the size of the radiator by 25% or even 50% (or fitting two instead of just one). The alternative is underfloor heating, but this really needs to be installed during construction and not as an afterthought.

Even if you don't fit a heat pump today, having oversized radiators means that you can run the existing (condensing ?) or new combi boiler at a lower temperature which should enable it to run at a higher efficiency.

Don't forget, a heat pump will (usually) require a hot water tank, so if you like hot showers, you should consider having an electric shower installed.

Can you qualify this statement. We heat out hot water tank once a day to between 45-50oC this time of year for an average of 1kwh of electricity with our heat pump and that include one legionella burn a week. 2-3 showers a day plus 2-3 sinks

There isn't an electric shower on the market to beat that for 14-21 showers and 14-21 bowls of hot water.

I would suggest the same is true for gas being a 1/4 of the price per kWh for electricity?

What are you basing your calculations on?

Section62

thebizz said:

Currently its a bungalow.  The whole back loft space will be converted into a dormer.  There will still be a reduced height loft space over a front bedroom earmarked for storage.  a  Currently, there is gravity-fed water feed tank in the loft.  The tank is calcified and is scrap anyway.  That whole space will be a bedroom with some amazing views.

Is the loft space going to have an en-suite or other plumbing in it?

Although you don't need to have a vented system, there's no fundamental reason why you can't have one in the setup you describe.  Beware that one (possibly flawed) decision isn't constraining the other options you have - e.g. if you (wrongly?) believe you have to go unvented and unvented costs as much as having a combi, then you can convince yourself that a combi is the right route.  It is much more important to work out what you need, and what is most economical, and then base other decisions (e.g. where to put storage) around that.

thebizz said:

The boiler is a Greenstar 15 which is rated for 10 radiators and we will need 11 radiators minimum (about 140m2).  We actually dont use that much heating and at least 3 of the radiators will be on tickover with the doors closed most of the time as are just spare bedrooms/2nd office.

The rating is only a guide really - especially as the size of radiators varies so much.  What you really need is a heating engineer to look at the required power output to heat your home, bearing in mind you could/should also be taking opportunities to improve thermal efficiency.

thebizz said:

The boiler is in a detached garage 1 meter away from the house.  So the heat from the boiler itself goes into the garage and then the hot water travels back to the house externally in a brick arch with pretty minimal insulation.

Is the garage staying detched?  Without seeing it I can't say for sure, but I'd be surprised if the optimum outcome for your project involved still having a detached garage at the end of it.  Some people would probably suggest conversion of the garage before changing the roof/loft.  I'd suggest that enclosing the space between the house and the garage (if possible) would have the benefit of turning a largish area of existing external wall into an internal wall.  Certainly something to consider.  Have you got an architect looking at issues like this for you?

thebizz said:

When we spoke to the plumber (briefly a while ago) he suggested a combi in the utility room or he could fit an unvented cylinder either in the garage next to boiler or sideways on in the low areas of the loft. Not sure if building regs or the plumber need to sign off the capacity of the boiler.  It was only fitted 2 years ago just before we bought the house so a shame to waste it but I think it will be underpowered.

Unfortunately some plumbers will only go with what they know.  I think you need advice from a heating engineer that deals with other forms of heating to get a more rounded range of options.

Dumping a 2 year old boiler is very unlikely to be an economic solution.  Even if sold for second-hand value, you are effectively throwing away years of sunk cost.  Thinking about a heat pump solution in the medium term, but retaining the gas boiler in the shorter-term, is more likely to be cost effective.

BUFF

Under the new Part L that came into force in England in June if this were a completely new installation then it would be designed with radiators sized for a maximum flow temp of 55C. For heat pump use 35C flow would be better (albeit I am sure that there will be improvements in heat pumps in the next ~15 years).
You possibly/probably also would need improved controls over those fitted even 2 years ago.

If you are planning to stay in the house at least as long as the next replacement cycle I ,too , am of the keep space for a stored hot water tank & probably keep the existing boiler for now.
Combis have their pros (space saving whilst giving mains pressure DHW) but they also have their downsides (they tend to be less efficient at heating hot water than a conventional or system boiler +tank, hot water often isn't as instantaneous as stored hot water especially if the boiler is far from points of use) & repiping for one only to have to redo it in the future to move back to stored hot water is extra expense.
You can get integral heatpump hot water tanks though which may be worth investigating if the multiple between the cost of gas & electricity continues to close. 

matelodave

Dont look at the bolier v number of radiators as it's just a rule of thumb - do a proper heat loss calculation and make sure that the rads are sized base on the heat loss of each room and base it on a low flow temp of around 40 degrees. That should enable you to work out the size of boiler that you need base on the heating load rather than a wet finger guess.

Most boilers tend to be oversized for the heating load. Sort out your heating controls and there's nothing wrong with an unvented tank. Just make sur that all the pipework between it , the boiler and the house is well insulated to minimise heat loss.

thebizz

The loft conversion will have a bathroom and shower so that is why a gravity-fed system will not work.  I thought the only options then were combi or an unvented system.
The garage will be staying as a garage as I want a garage. Actually considering extending it another 5m as I want more garage.  We did consider converting it but that would just mean building another garage.  The space between the house and the garage may be covered but it will still be 'outside' as it's the main walkway from front to back.  The design was done between us and the architect and may not be perfect but ticks a lot of boxes.   Foundations were started yesterday so a major redesign is not on the cards.
We could insulate the pipes that run externally.  Could easily box a square foot off which would be pretty hidden and fill with insulation.
I agree the trades go with what they know.  Air source pump costs 13 times more than a combi supplied and fitted from scratch from gas supply.  I can't understand how that can be but that what we were quoted (minus 5k sub)
We had similar looking at different building techniques like modular and sips.  They should be cheaper alternatives but the reality in Cheshire doesn't seem to be the case at the moment in my experience.  I think this would be different if in more expensive locations paying 5-6k m2
Our plans were registered before the 15th June so new rules do not apply but we have specified insulation above the requirements where we can.  I'll check with the plumber regards pipe flow rates we can reasonably get at this stage and get as much as is financially sensible.
All the plumbing will be close together.  The utility is next to the garage which would be the internal location for any boiler move. The placement for the heatpump will be on the garage wall about 2 ft from where the current conventional boiler is   Space for unvented cylinder is directly above the utility. The kitchen and main upstairs bathroom are adjacent to both points. The fuse board is next to the utility and all of it will be servicable through the eves for access to wiring plumbing without too much disruption to the house.  There is a downstairs bathroom and cloakroom on the opposite side of the house but they will not get much use.   The above means if we did go with a combi and it lasted its 10 year warranty period then we could move to a heat pump relatively painlessly.  How much more we spend in that 10 years who knows.  Currently looking at about 2k a year on combined energy costs after the last price rise and a good chunck of that are fixed costs.  Whilst I am sure we are in for further increases it is difficult to get a balance of what is cost-effective.  We did have a discussion about digging all the existing flooring up (which just seems to be a very thick concrete slab) and adding insulation but it just doesn't add up financially and after the energy to remove the concrete, produce pir and concrete and all the transport involved I am not sure it adds up environmentally either.  
Any suggestions on a good balance for the glazing.  We are adding 2 4m bifolds (maybe sliders) a 3x1.5 lantern and 2.5m Juliet balcony along with 3 other new windows and 3 replacement windows (20-year-old double glazed units but in good condition) and 2 external doors.  One a 10 year old pvc unit the other a wood door.
As we got build regs registered early enough we don't have to have trickle vents as long as they haven't already switched over their tooling).   Where do we people think the diminishing returns kick in with the glazing?

FreeBear

thebizz said: The loft conversion will have a bathroom and shower so that is why a gravity-fed system will not work.  I thought the only options then were combi or an unvented system.

You can also get pumps that will boost the pressure enough for a shower. A low cost one - https://flowflex.com/shower-power-booster