Which heating option? Going round in circles

[WGL]

Need some external opinions and advice please. Thought it best to post in this section as I want to go back to first principals.

 

Going to begin renovation and extension on my 1960s house in the new year. It'll be broadly up to new build regs when finished. It's also going to be large (130m2 footprint and 3 storey) - because as a builder myself, why not? Just finished my heat loss calcs and with an 80% efficient MVHR system it'll be 4.8kw at DT of 18.

 

Struggling with the heating option though. Currently have a rock solid but inefficient old natural gas boiler, 28mm main pipework and 22m to 15mm rad connections. I have a small log burner also. Giant asbestos header tank in loft so going to stick with a vented DHW option of some sort as I'm not getting that down. Very good mains pressure. Plan on having Solar PV with battery storage. Will need to change my rads regardless of option.

 

Options as I see it;

 

Small gas heat only boiler

PROS; Cheap straight swap, given the heat needs will be cheap to run, easy DHW solution and an all round known quantity so I'm happy to run pipework and connect rads (done lots of this in past), heat only boilers are pretty reliable as they're so simple

CONS; Not Eco

 

ASHP

PROS; Existing pipework suitable, cheap to run, eco 

CONS; worried an installer is going to way over specify and subsequent cost will be enormous (even with grant), concerned installer won't allow me to do the installation donkeywork and save money, we don't like it warm at night so a constant temp is not ideal, DHW a bit more of a faff than with gas

 

A2A heat source

PROS; with solar PV and storage negligible running costs, virtually free cooling, no rads, eco, more instant heat than ASHP, potentially better air quality if filtered???

CONS; how to recirculate the heat around a large house? no DHW, similar over-specification concerns to ASHP, not as easily configurable as an end user (seems to vary wildly between manufacturers also), less room by room control

 

The A2A would be my preference really, but I discounted it because of the problem of evenly distributing the heat. Only back in consideration as the heat loss figures are so low. Is it conceivable to design the MVHR or some other ducted system to evenly distribute the heat cost effectively? They're large rooms, but it's definitely not open plan.

 

I appreciate all input and thanks in advance. Will

 

[JohnMo]

29 minutes ago, WGL said:

4.8kw at DT of 18.

Not sure about using a dT of 18, so a design temp of -3 would be 24! So heat demand is closer to 6kW

 

33 minutes ago, WGL said:

Is it conceivable to design the MVHR or some other ducted system to evenly distribute the heat cost effectively

No, useless you have passivhaus heating requirements.

 

ASHP v gas boiler DHW complication - there is no difference. Both have a cylinder with a coil inside, ASHP just has a bigger coil and slightly bigger cylinder.

 

Well insulated house with constant background heating don't feel hot, MVHR gives you fresh air constantly. A small setback at night job done. You don't have to heat bedrooms as much as the rest of the house.

 

Look on eBay cheap ASHP come up the time, I paid £1300 for mine, other on here way cheaper.

 

I got my completion certificate in March with a gas boiler, installed an ASHP the same month. Mainly for cooling, which gas boilers aren't good at.

 

 

[WGL]

Thanks JohnMo, you were very helpful with my heat loss query yesterday. Sorry, Noddy question coming; If I factor an outside temp of -2 (I'm in South Devon so mild winters) and inside temp of 20 degress, what DT should I use?

 

I hadn't even thought 2nd hand was an option! Can you give me (or direct me to) some information about your setup please? How did you install and commission it? How does the cooling work? Anything and everything you've got really.

 

I've got my 18th Edition and Part P electrical qualifications, plus loads of experience with plumbing, so if it was possible for me to do the work that would be amazing.

 

Thanks again.

 

Will

[JohnMo]

1 hour ago, WGL said:

outside temp of -2 (I'm in South Devon so mild winters) and inside temp of 20 degress

22 = (-)2 + 20

 

2 hours ago, WGL said:

hadn't even thought 2nd hand was an option

Buy new, mine was brand new, still in manufacturer box.

 

Cooling you need UFH or fan coils, doesn't work with rads.

 

Mine is as simple as it gets, ASHP, piped to 3 way diverter. One way goes to the cylinder, the other to UFH. Have a single thermostat to start stop the ASHP.  Buts runs 24/7, on weather compensation. UFH has no pump, mixer or actuators.

 

But go into the plumbing and ASHP sections, on the forum and have a read up. You need to do loads of reading up and decide what may work for you and ask questions.

[Temp]

4 hours ago, WGL said:

Giant asbestos header tank in loft so going to stick with a vented DHW option of some sort as I'm not getting that down.

 

Could switch to mains pressure and just disconnect the tank leaving it in place.

 

Main consideration would be the condition of the pipes. Good enough for mains pressure?

[Adsibob]

3 hours ago, JohnMo said:

No, useless you have passivhaus heating requirements.

I’m not so sure about this. We modernised and extended a 1930s semi, spending a lot of money on making it airtight, insulating it* and installing a very good MVHR system (Brink Flair 400 which has an efficiency of 95%) and we manage to get away with only heating the ground floor and only heating the kids bedrooms on the first floor for a couple of hours before bedtime. This keeps the first and second floors warm enough for our purposes. My wife occasionally complains that our master bedroom is too cold, but this is nonsense; it hasn’t dropped below 18.5C this last week, and is only heated (at the moment) from indirect heat from the ground floor below and MVHR.

 

 Whilst we still have some variance between rooms and zones, I think the mvhr is helping reduce our bills a lot.

 

i would however be concerned by a 80% efficient machine. Why not get something better?

 

*our insulation is not top spec. We only have 2G windows, except for one 3G velux, and our EWI is not particularly thick, about 45mm.

Edited November 4, 2023 by Adsibob

[JohnMo]

19 minutes ago, Adsibob said:

I’m not so sure about this.

Question was

 

5 hours ago, WGL said:

Is it conceivable to design the MVHR or some other ducted system to evenly distribute the heat cost effectively?

Ventilation systems to passivhaus spec can carry 10W/m2 equivalent heat output. Any more than that the air smells burnt. Reference is from passivhaus institute. The original poster will have a heating requirement of circa 6kW over 390m2, so 15W/m2, 50% above passivhaus standards.

[SteamyTea]

5 hours ago, WGL said:

Is it conceivable to design the MVHR or some other ducted system to evenly distribute the heat cost effectively? They're large rooms, but it's definitely not open plan.

It is possible to use a ventilation system to move heat around. Just a case of making it bigger, or moving air though it faster.

If you have the room, larger ducts are easy to fit, takes some careful designing to not look odd, and watch out for room to room crosstalk.

 

Quite a few of us on here do not have heating upstairs, we just rely on natural convection and conductance through the ceiling from below.

[JohnMo]

11 minutes ago, SteamyTea said:

It is possible to use a ventilation system to move heat around. Just a case of making it bigger, or moving air though it faster.

If you have the room, larger ducts are easy to fit, takes some careful designing to not look odd, and watch out for room to room crosstalk.

 

Quite a few of us on here do not have heating upstairs, we just rely on natural convection and conductance through the ceiling from below.

But you are using MVHR, so your ventilation losses also increase if you increase flow rates, so you end up down a rabbit hole...

[Adsibob]

All I’m saying is my heating bills are much less than you would expect given my house is now a 2300 square feet part 1930s semi, part new build, and I’m sure a big part of that is from mainly restricting our heating to the ground floor and half the first floor, and having a very efficient MVhR system.

[Mike]

2 hours ago, Adsibob said:

i would however be concerned by a 80% efficient machine. Why not get something better?

I'd agree - there are independently certified MVHR units in the Passivhaus database that recover over 90%. Their testing regime is rigorous and often more reliable than manufacturer's figures (Heat Space & Light have an article explaining why these can be misleading). Although the Passivhaus 'Efficiency Ratio' is generally a better guide than the heat recover rate, as it also takes into account electricity consumption.

 

59 minutes ago, SteamyTea said:

It is possible to use a ventilation system to move heat around. Just a case of making it bigger, or moving air though it faster.

This. There are even (rare) whole-house warm air heating systems, but they'd need separate ducting from the MVHR system to avoid the problem mentioned by @JohnMo.

 

However, depending on the heat load, an MVHR-compatible scheme might be possible using in-duct post-heaters. Typically only 1 is used after the MVHR unit (or maybe one one per floor), but depending on the ducting scheme more could be used - even one before every ceiling outlet - provided the duct air stays below 50°C (from memory) to avoid the burning smell mentioned above. Zehnder produce a 4kW hydronic one (ref 472901857), for example, that could connect to wet central heating.

 

Personally, I'd probably install UFCH instead.

 

Edited November 4, 2023 by Mike

[JohnMo]

14 minutes ago, Mike said:

Zehnder produce a 4kW hydronic

But don't connect to an ASHP, as the temps required are not a good match.

 

Keep it simple

[SteamyTea]

1 hour ago, JohnMo said:

But you are using MVHR, so your ventilation losses also increase if you increase flow rates, so you end up down a rabbit hole

You can have both.  One system to move air around the building, and then the MVHR.

A bit of clever design and the MVHR can be 'injected and extracted' from the air handling unit.

 

  

26 minutes ago, Mike said:

This. There are even (rare) whole-house warm air heating systems, but they'd need separate ducting from the MVHR system to avoid the problem mentioned by @JohnMo

Yes, as I said, design on the system is everything.

Edited November 4, 2023 by SteamyTea

[Mike]

1 hour ago, JohnMo said:

1 hour ago, Mike said:

Zehnder produce a 4kW hydronic

But don't connect to an ASHP, as the temps required are not a good match.

It may or may not be, depending on the heat output required. Which is why I said it might be possible.

[Adsibob]

1 hour ago, Mike said:

Personally, I'd probably install UFCH instead.

Agree.

mvhr is good, but for various other reasons, not as the dominant heating system. 
 

2 hours ago, SteamyTea said:

It is possible to use a ventilation system to move heat around. Just a case of making it bigger, or moving air though it faster.

If you went down this route, wouldn’t the increased airflow dry out the place too much, such that you would need an enthalpy exchanger thingy as well as a heat exchanger? 

[SteamyTea]

8 hours ago, Adsibob said:

11 hours ago, SteamyTea said:

It is possible to use a ventilation system to move heat around. Just a case of making it bigger, or moving air though it faster.

If you went down this route, wouldn’t the increased airflow dry out the place too much, such that you would need an enthalpy exchanger thingy as well as a heat exchanger? 

Possibly, it would depend on the starting conditions.

Doubt you would ever need to increase humidity down here.

[JohnMo]

12 hours ago, Mike said:

It may or may not be, depending on the heat output required. Which is why I said it might be possible.

 

Bet the guys more confused, than he was before asking the question.

 

If you are going to start suggestions such as heating MVHR, at least look at a data sheet, there is a heat loss of around 6kW, when you factor in the correct dT. The house is 390m2, so a ventilation rate will be 200m3/h or less.  A post heater at 55 deg water flow rate and 212m3/h carries 2.5kW.  so massively unsuitable for this application.

13 hours ago, SteamyTea said:

You can have both.  One system to move air around the building,

That is practical terms would be a ducted A2A heat pump. 

[Adrian Walker]

Back to basics.  How well insulated and air tight is the renovation and extension going to be? A drawing/sketch would be useful as would some photos.  What do you mean by "broadly up to new build regs"

[WGL]

Thanks everyone. A lot to take in there, but it's all appreciated.

 

I wouldn't be averse to installing a separate 'air recirculation' ducted system in addition to MVHR and wall mounted A2A. Not the most outlandish thing I've done over the years, but I suppose the devil is in the detail. I expect significant solar gains as main elevation is due South with the bulk of the glazing, so recirculation would aid with that. I anticipate installing aircon at the top of the 2nd floor landing regardless, in order to help alleviate overheating.

 

Now I've done my calcs correctly 🫣6kw is the figure. Would rather go for 90% MVHR, I'm just playing it safe with the calcs at this stage.

 

I can see me not having to heat the upper floor much in practice. Done quite a few loft conversions and often the customer ends up switching their rads off, plus they're guest beds anyhow (unless my folks move in of course).

 

Dry air will definitely not be a problem. It's effectively temperate rainforest out my back door.

 

UFH is out really unfortunately. The ground floor extension which has a concrete floor is basically kitchen units and a games room for the kids (pool table slapped in the middle). The main ground floor living area is suspended floor currently and in good condition so not concreting it, just going to insulate and airtight.

 

I'll get together floor plans? They're all on autoCAD at the minute, so I need to play around with formatting first. Would be great to get opinions from all angles.

 

Walls 0.18, Roof 0.16, Floor 0.18, timber DG argon low e. I'm doing the work myself so airtightness will be much better than on a site in reality. As a builder I know where the corners get cut unfortunately. 

 

 

Edited November 5, 2023 by WGL

[WGL]

I've attached a pdf of my floor plans. North is at the top of page. Would be great to hear what others think regards M&E in general tbh. I'm looking to situate MVHR unit and any main heating source in the 'plant room' next to the utility ideally

 

If I stuck with a vented cylinder arrangement, that would likely be in a cupboard in the first floor bathroom (not shown on plan) as that is where the cylinder is currently. If we went with unvented, that would be in the plant room.

 

As stated prior, air con unit would be situated at top of loft landing space eventually (there is a section of flat roof for the external unit to sit on). If I could get away with a large A2A as the primary heating, would be good to situate there I think. I suppose I wouldn't have a problem with siting any of the other systems up there if it worked more efficiently.

 

I'm open and appreciative of all suggestions. Thanks in advance. Will

formatted floors 11-23.pdf