Gas boiler or heat pump

william

Hi. Have researched heat pumps extensively and am still undecided whether to go with a gas boiler or heat pump.

250m2 1950s house is being refurbed this Autumn. There will be 150mm ewi and triple glaze throughout. Suspended floors will either be replaced with insulated floor slab or retained and insulated beneath and within. Will definitely be replaced if we go with heat pump as ufh will be chosen for ground floor. Attic heavily insulated. Aereco demand control ventilation without heat recovery. Large family with high water usage. Can install solar to help with this if needed

Comparing projected running costs is where I’m having difficulty.

With the house so well insulated, would the gas bill be very low? Would there be little gas consumption throughout the day, in the evening the boiler would cycle on and off as required. The heat pump is on all day maintaining a steady temperature

Am I missing something in my logic that the heating requirement is so low that gas is the cheaper and simpler option?

Thanks

William

graememk

Without knowing the projected heat loss/ estimated heat required for the year.

You can look at it in simplified terms.

A condensing gas boiler well installed and sized correctly, will be 95-99% efficient so for every kwh of gas you use will be 0.95 -0.99 kwh of heat.

A heatpump well installed and sized correctly should easily hit a efficiency of 400% . 1 kwh of electric is 4kwh of heat.

Bonkers is showing a gas price of 11c from flogas right now.

Water power is currently the cheapest 24 hr rate at first glance on bonkers at 38c

At the current prices

A kwh of heat from gas will be 11c

A kwh of heat from a heatpump is 9.5c

I would also say to get solar no matter what heating source you are getting.

Alkers

Are you planning radiators or underfloor?

How many bathrooms / showers?

Make sure you address air tightness in the works.

Gfch is still the winner for me currently, a lot of people, particularly in new build estates are having a lot of issues with large bills on heat pump systems, you might get better attention to detail on a one off install

the_amazing_raisin

If you're getting a heat pump then you'll need to consider this in the design of the pipework and underfloor heating

First thing you'll need is a heat loss calculation for each room and the whole house (which is basically the sum of the rooms)

You can do this twice, once for a low water temp heat pump and again for a higher temp gas boiler.

This all feeds into what size heat pump or boiler you need. You basically pick the next size above the required heating input for the whole house. It also determines the size of emitters you need in each room and what size pipework you need

You can do the calculations yourself, there's online ones where you can put in each room data and it does the heat loss calculation. Here's one example

https://openenergymonitor.org/heatlossjs/

You'll probably want to engage a heating engineer to spec up the installation. If the engineer says you don't need those calculations then get a new engineer

Similarly if they come up with a completely different answer to your calculations then question them extensively on this and get them to justify their position

Also subscribe to the YouTube channel Heat Geeks and read the blog below

https://trystanlea.org.uk/

Another option is a midway conversion. You could probably keep the existing boiler but size the emitters and pipework for a heat pump and also provide the outdoor pipework to where the heat pump would be located. That means a heat pump would effectively be a drop in replacement, or could be used to supplement the boiler

alexf1

Thats a big house! How much will a heatpump cost v's gas boiler?

My dad is a plumber and recently installed a heatpump for a client. The size needed was €8500, compared to a top spec gas boiler that would have cost €2000. There is some underfloor heating but the end result after the experts set up the heatpump was 320% efficiency, which is still amazing, but you'll be a very very long time making back the difference is initial cost. The other thing to think about is replacement when the boiler/heatpump goes kaput. I recently had to replace my gas boiler at a cost of €1350 + installation (my dad did it in a few hours for no charge thank jebus). A heatpump for my size house would cost €5000 just to buy (thats a price that would have broken me if I had one of those that failed during the freezing cold winter). I don't know how long heatpumps are warrantied for of how many are failing after 5 or 10 years but it's another factor.

I love the idea of them as they are more efficient, but in a similar way to buying an EV, saving the planet is only for the well off!

Water John

Well, with the level of works, the One Stop Shop SEAI house grants need to be factored into your capital outlay. To draw the grants you will have to go the HP route.

ColemanY2K

Just to reiterate a point made above, whatever you decide to do be sure to include PV as part of the solution.

Busman Paddy Lasty

You have so many choices, have fun working it out! As others have said get solar regardless, it works in Ireland and feed in tariffs are here.

Capital cost I would look at rather than running costs, was in your position two years ago but went with combi gas boiler instead due to capital budget.

Do you have any wider goals? Like getting an A rating? Having stable temperature all day if you're retired or working from home? Do you want a heat pump even IF it never pays for itself, i.e. for environmental reasons?

My 2 cent, get rid of suspended floor. Replace with fill, insulation and screed. Much better comfort to have some thermal mass in the screed, even with radiators this makes a difference.

Airtightness and edges/joins in building fabric. Thick insulation can be undermined by poorly installed windows or thermal bridging through the window reveal. Maybe someone who got a heat pump can advise on their airtightness methods. For us with no such airtightness requirement, focused on window reveals and other joins in the building.

Do you have any fireplaces in the house?

Baseball72

Following a fire earlier in the year, I have to undertake a rebuild of my 3-bed semi (about 900sq.ft). The four walls are fine but a new roof is required and a complete re-fit of all the rooms. It's an opportunity to start afresh and end up with a very well-insulated house. Should I continue with gas central heating, or consider the heat pump option? There is one fireplace in the house. Any suggestions would be appreciated.

graememk

Insulation, insulation insulation.

No matter the heat source it will be cheap to keep warm.

Fireplace, if you want to keep it, look about taking an external duct to feed it.

Water John

I would dig down 400mm and do the floor insulation and UFH as well.

the_amazing_raisin

Yeah I would recommend doing the insulation as well and maybe sizing the pipework and rads for a heat pump even if you stick with the gas boiler

As far as I can tell there isn't really a disadvantage to oversizing the pipework and rads for a gas boiler other than it will heat a room very quickly and might overheat it a bit.

So you'd probably end up short cycling the boiler or turning it down all the way, which means it might not operate at it's peak efficiency

But it does mean you can just drop in a heat pump when the money becomes available, or when the boiler goes kaput and that's your preference

MightyMunster

https://www.boards.ie/discussion/comment/120648388#Comment_120648388

On the replacement costs, aren't new gas boilers gone from 2025 or something? So a new boiler/heatpump installed now will have to be replaced with a heatpump no matter what you choose this time.

graememk

https://www.boards.ie/discussion/comment/120653634#Comment_120653634

On new builds, not new gas boilers in general

Water John

You can also put a mixer system in if you're using a high heat source like a boiler with UFH or HP rads. Mixes the water down to 40 degrees, leaving your boiler run at its correct temperature. If you change over to a HP you don't need to alter anything.

william

Thanks everyone for getting back. Very useful and helpful information. We got a technical assessment done and can get the property to B2 (windows, ewi, insulation between floor joists) or A3 (with ground floor slab and insulation). All fireplaces to be blocked up. We have 1 bathroom and 1 shower room.

Will 100% go with PV.

The house is currently E1 and heat use is 36,000 Kwh/year. I don't know what that goes down to for a B2 and A3. If I had that then I could do the maths using "A kwh of heat from gas will be 11c c v A kwh of heat from a heatpump is 9.5c" to see the differential in running costs.

The UFH would be ideal. We're told that we'd have to vacate the house for 2 months though which would be very difficult for us. This in itself is swinging us away from a heat pump.

DC999

https://www.boards.ie/discussion/comment/120654847#Comment_120654847

Wow. We use 6000kWh of gas a year for heating. But it's a small gaff and don't mind it colder than most.

So if you use 35000kWh on heating, leaving the house for 2 months could be worth it. Get the best insulation and good heating setup and that will drop a lot.

Worth also looking at how it's so high.You could tweak how u heat the house and that might save a lot too. All the best with it

the_amazing_raisin

https://www.boards.ie/discussion/comment/120654647#Comment_120654647

Oh that's cool, hadn't seen them before

Some look like they go down to 35C, so you could size the pipework for a heat pump and still run the boiler at its normal temp

Water John

Yeah, worked for company that supplied UFH systems.

graememk

https://www.boards.ie/discussion/comment/120655143#Comment_120655143

Some gas boilers can modulate down to that temperature/heat load too and not have to cycle.