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Electrical supply - Replacing Oil Boiler with Heat Pump

CraftBeer

Hi. When my external oil boiler gives up the ghost i'd like to replace it with an Air to Water Heat Pump.

This is a 1980's house that has been recently renovated, so there's a new fuse board in the kitchen.

When installing a heat pump, would it be possible to re-use the existing electrical cable that supplies the oil boiler? It's a Grant oil boiler that (according to the online manual) requires a 230v/240v ~50hz supply. I'd like to avoid digging up the patio just to upgrade a wire!

thanks.

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meercat

https://www.boards.ie/discussion/2058224397/electrical-supply-replacing-oil-boiler-with-heat-pump

It’s unlikely the cable would be big enough to take the increased load.

2011

Heat pumps would typically require a cable that is at least 6 mm sq. and in many cases 10 mm sq. Whereas oil boilers would tend to use a 1.5 mm sq. cable.

FYI: I have talked to some experts about heat pumps (Ideal Homes exhibition), the general consensus is that they will only work on A rated homes.

In the wind

Grüezi don't know the answer to your specific question but I would be very cautious going down the air to water heat pump route myself on an older house or even in general. I feel they're a bit of a fad at the moment and electricity prices are on the up and up.

I'd advise reading up as much as you can from truly independent sources. I'd be looking at UK and Irish youtube channels on the subject if I was in your position.

2011

https://www.boards.ie/discussion/comment/118376990#Comment_118376990

The cost of coal, wood, gas and oil is escalating too! What would you suggest?

The advantage of heat pumps is that the heat energy output is higher than the electrical energy input.

CraftBeer

Thanks for the comments.

Perhaps i can still avoid disturbing the patio by branching off the existing conduit which was buried in the back garden and currently supplies electricity to the shed?

Regarding heat pumps - i think we'll be ok. The Oil boiler temp is set to the min (60c) but the rooms get too hot after 45 mins. House is internally insulated, triple glazed, thick insulation in the attic, new steel panel rads and all new qualpex piping under the floors. When putting down the patio we also replaced the old water pipe to the boiler with expensive pre-insulated pipe, but unfortunately i didn't think about replacing the power supply. Will obviously get independent advice before pulling the trigger on a new heating system though.

JL spark

Your going to need a independent supply from main DB in the house , and then a communication cable and power back to the in door unit depending on what system you use ,

Irish Steve

A few thoughts, based on a lot of research and investigations.

Home is an early 90's dormer bungalow, traditional cavity solid block inner and brick outer, with some polysytene in the cavity from new, under a tile roof. Subsequent upgraded to add pumped bead cavity insulation as approved etc by SEAI, heating is still oil boiler to radiators, with a slightly non standard hot water system as it uses a heat exchanger external to the tank, which is brilliant as we get HOT water from one pass, and the top of the tank is ready to go 10 minutes after putting the boiler on, so we can run for a shorter period of time if we don't need a full tank of hot water.

We went to an energy day sponsored and run by the local authority a couple of years ago, and as a result, one of the companies that was displaying came out to see what we would be looking at to put a heat pump in. He went through things, and was very fair, and open, and told us that as the house was at that time (BER of C2 after the cavity pumped work) he would not be happy to install a heat pump, as the running cost would be too high, and the cost of installing would also be high due to having to change all the radiators (19) to larger aluminium radiators, and change some of the hot water system, as the heat pump couldn't provide the temperature needed to heat the hot water to a high enough temperature, and the radiators would have needed changing as the heat pump operates most efficiently at a lower water temperature than the temperature used to size the original radiators, so they would be inadequate for heating the rooms after the change. A heat pump temperature for best efficiency is closer to 35 to 40 degrees, and that will make a significant difference to the heat output from the radiators, as well as issues for hot water temperatures.

His recommendtion was that we needed as an absolute minimum to get the roof insulated to a level that would prevent air circulation issues, and the windows would need a better level of heat retention to make the upgrade even worth considering, and we'd have to use electric heating as a top up to get an acceptable hot water temperature, and having done a lot more research since that time, I now understand where he was coming from, and he was right. Some of the operating costs being reported for heat pump installs only serve to bear this out, and I'm very happy that we've done other things first.

Due to the nature of dormer, the roof void leaks heat like a sieve, there was some fibreglass in it, nowhere near enough, even with what I'd added, we already had our suspicions, and having had the roof and rafters foam filled early in 2021, I know exactly where he was coming from with that, just that one change alone has made a significant difference to the heat retention in the house, without changing anything else at the moment, though we were also able to upgrade one bedroom window and the glazing in the patio door, that's also made a difference, and ideally, we'll be doing other windows over the next while.

The cost of upgrading the boiler to a condensing boiler is an interesting one, in that the cost of the boiler probably won't be recovered from the oil savings over the number of years we're likely to be still living here, and changing the radiators to upgrade to a heat pump is bluntly a non starter unless the Green party come up with some real incentives rather than the joke figures they're offering right now.

I made a mistake (according to them) by putting multi zone controls and thermostatic valves in over 25 years ago, so they don't think we deserve a grant for a smart system to make it possible to control the system when we're out of the house, and I can do that job myself for a fraction of the sorts of sums being quoted for the job, even allowing for the supposed saving from the grant.

Under floor heating is not an option unless we tear up over 200 Sq Mtrs of tile flooring downstairs, which isn't going to happen.

Heat pumps can't efficiently produce hot water at 60 C (needed to ensure that Legionaires doesn't proliferate) unless it's done as a 2 pass unit, and they are expensive, and need more floor space to put in, so that means either going for a solar system, or using electric to run an immersion heater, either from mains or using PV solar panels, which again adds significantly to the cost.

Some of the systems being offered at the moment are being sold by snake oil salesmen who won't be around to deal with the issues when the problems start, as they will have moved on to the next hot sales option, and the only reason they are even getting air time is because the relevant political people are desperate to be able to have what appears to be a "green" option going forward, and for the vast majority of houses in this country, the cost of installing those options is only frightening, even more so if you're over 50, as the time to pay back means that the present owner won't have a hope of seeing a return on the investment. They're not going to say it, but in a lot of cases, especially some of the Celtic Tiger construction over the last 20 years, it would be cheaper to demolish and rebuild than it would be to retrofit, but they're not going to be suggesting that any time soon.

If you don't believe me on the salesmen moving on, how many offers have you seen recently for wood pellet boilers for domestic installations? I can't remember seeing one for a while now, maybe because the problems of getting deliveries of bulk wood pellets meant they never became readily available, and the hassles of having to carry multiple bags of pellets to the boiler loses it's appeal VERY rapidly, and there are also significant reliability issues, based on some of the comments in various support areas on line.

For the original poster, I wish you luck with your search for a solution, I hope you find one, as I fear that you may not get the results your hoping for.

In the wind

https://www.boards.ie/discussion/comment/118377557#Comment_118377557

I'd suggest oil or gas in an older house.

JL spark

I could be wrong , a customer we are working for is going to install a heatpump/oil unit ,

think the oil brings unit up to temp and heatpump kicks in then , won’t know more for a few months ,

Wearb

There seems to be hybrid systems available.

https://www.grantuk.com/products/hybrids/

2011

https://www.boards.ie/discussion/comment/118379100#Comment_118379100

"House is internally insulated, triple glazed, thick insulation in the attic"

This description tells us very little about how good the insulation is. Is the house airtight? How much insulation in the attic and walls? Are the doors composite? Are there letterboxes in the external doors?

If the overall insulation is not sufficient, a heat pump will not be a cost effective solution.

It is very, very difficult achieve even a B1 level BER for a home built in the 1980's

"new steel panel rads"

These rads would have been sized for a oil boiler (high grade heat source), therefore they will be undersized for a heat pump (low grade heat source). In fact most people that use heat pumps have underfloor heating for this very reason.

I am a big fan of heat pumps, but only when properly installed in a home suitable BER.

Having said that, I admit I am not an expert in this area. I am just repeating what I have been told by those that are experts on heat pumps. I think you should start by having a BER assessment on your home.

Ubbquittious

https://www.boards.ie/discussion/comment/118376954#Comment_118376954

That is a lot of mm sq

Arent the single phase heat pumps only 2-3kw?

2011

https://www.boards.ie/discussion/comment/118387099#Comment_118387099

The last one I installed was around 9 kW

Bruthal.

The cable size should be the sizes suggested, rather than the calculated minimum anyway. A 9kw 3 phase would suggest 2.5 is OK. But a decent few meters of a run and the compressor might struggle to instantly start without causing a large voltage dip at the heat pump.

[Deleted User]

I had an air to heat mini split heat pump installed earlier this year. I actually wanted it for AC rather than heat. The installer told me I needed a dedicated electric supply from fuse box with it's own RCBO. Cable size was 2.5 as far as I remember.

I do use them for heat too & they are quite good but I still have my gas boiler for the colder days. You need very good insulation. Air to water is a totally different ballgame. Air to water is really for homes with underfloor heating. You can hook them up to your existing central heating system to replace the oil boiler BUT you will need to increase the size of the rads. Typically you'd need to double the rad size per room. When you use air to water you use it differently to the way you'd usually use rads. Rads don't get as hot & it takes a long time to heat up the house. You don't put the heating on boost for an hour or two. You'd be more likely to turn on the heat in October & off again in April letting it run 24/7. Personally I'd be looking at replacing the oil boiler with a new oil boiler rather than a heat pump unless you have A rated home with underfloor heating

I think air to water is cheaper than oil & gas with outdoor temperatures 5c & above. Below 5c & oil/gas is cheaper. Ground to water is the way forward for new builds but expensive to get in after the builders have left the site