# Cost of installing back boiler



## CurtainCall (16 Jul 2015)

Would anyone have a rough idea how much it cost to install a back boiler to an open fire?  There is gas heating so the radiators are here.


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## dustie (8 Sep 2015)

Hi, We did this in our house last year. I wouldnt recommend doing it unless you are also installing a closed appliance such as a stove as you are unlikely to see any savings. Open Fires are approx 30% efficient, while a stove is closer to 80%. The stove cost approx 1k and the retrofitting the backboiler came in about 2.5k. The lads ran the pipes up the wall in room and through the ceiling to the cylinder in hot press upstairs. It was a lot of money but we were doing it as open fire was disaster and relying on oil with a small baby was so expensive. We used approx 300euro of oil last year (just to top up when fire was off). The previous year is was closer to 1300. We did also use about 450 on coal (versus 200 previous year). But aside from the financials the heat is amazing. We were running the stove Monday-Friday most weeks (tended to visit family at weekends). It took a bit of fine tuning but our initial complaint was it was too hot at 23deg upstairs. Have a good balance now. Definitely recommend it but get a good plumber to retrofit.. some guys specialise in this. You will get a recommendation from most shops which sell stoves.


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## Shane007 (8 Sep 2015)

I wouldn't mix solid fuel with a gas boiler unless in conjunction with a heat exchanger such as the Firebird heat exchanger. 
Most gas boilers must be on a sealed system and solid fuel must be open vented. This can be done with the FB. 

If both sharing an open vented system, sludge will kill the gas boiler as you won't be able to stop occasional pitching from the solid fuel when overheated.


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## conor20 (16 Sep 2015)

We installed a wood burning stove with a back boiler (in a typical three bed semi) last year to reduce our gas costs and I definitely recommend it. I calculate it's saving us €1,020 in gas per year. We went for a relatively high end stove which worked out a little more expensive - it came in at €4000 all in (wood stove with back boiler, new bigger and better insulated hot water tank and all the plumbing to hook it up and the installation of all of the above).  You might be interested in the maths I had worked out for it:
We have an efficient condensing gas boiler at the moment, but never the less, every hour it runs, it consumes 2.3m^3 of gas (25.3 kWh of gas per hour, and it costs €0.06 per kWh right now). That means the boiler costs €1.52 per hour to run. The carbon tax is levied on top of this: gas produced 0.23 kgCO2/kWh, which adds about €.10 per hour, so all up, *the gas boiler costs €1.62 per hour*. One thing to note is that gas is at a record low in price and is predicted to increase considerably as the US shale boom calms down. The carbon tax is likely to increase over time also. The price of wood will likely stay relatively flat, particularly if you have some land to grow it yourself.
Before we installed the wood burning stove, we ran the boiler for about 3 hours per day outside of the warmer months, so that's 3* 7 = 21 hours per week about 8 months of the year. Per week, that was 21* 2.3 = *48.3 m^3 of gas*, which is 21*25.3 = *531.3 kWh* of gas, which is 531.3kWh  * €0.06 = *€31.88 per week. *For 8 months a year, that's €31.88 per week * 32 weeks = *€1,020.16 per year to heat the house with gas. 
*
The wood burning stove has done away with about 98% of this gas heating - we only ever turn it on for ~20 minute periods in the middle of the night if we want heat right away.

In summary, the stove saves €1,020 per year in gas costs, and so at a cost of €4000 *will pay for itself in just under four years*, and with a lifetime of about 15 years, will save 11 * €1,020 = *€11,220 *in total, which is a pretty good return on investment.

The icing on the cake is that it completes the sitting room - we love sitting by the fire. I'd guess we watch about 50% less TV because the fire provides a focal point of the room that isn't the TV. So we've definitely had a great experience so far with the wood stove + back boiler setup.

Conor.


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## Slim (16 Sep 2015)

We installed a back boiler last year in a house that has OFCH. Cost was €980 all in. We are well outside major cities.


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## Shane007 (16 Sep 2015)

conor20 said:


> We installed a wood burning stove with a back boiler (in a typical three bed semi) last year to reduce our gas costs and I definitely recommend it. I calculate it's saving us €1,020 in gas per year. We went for a relatively high end stove which worked out a little more expensive - it came in at €4000 all in (wood stove with back boiler, new bigger and better insulated hot water tank and all the plumbing to hook it up and the installation of all of the above).  You might be interested in the maths I had worked out for it:
> We have an efficient condensing gas boiler at the moment, but never the less, every hour it runs, it consumes 2.3m^3 of gas (25.3 kWh of gas per hour, and it costs €0.06 per kWh right now). That means the boiler costs €1.52 per hour to run. The carbon tax is levied on top of this: gas produced 0.23 kgCO2/kWh, which adds about €.10 per hour, so all up, *the gas boiler costs €1.62 per hour*. One thing to note is that gas is at a record low in price and is predicted to increase considerably as the US shale boom calms down. The carbon tax is likely to increase over time also. The price of wood will likely stay relatively flat, particularly if you have some land to grow it yourself.
> Before we installed the wood burning stove, we ran the boiler for about 3 hours per day outside of the warmer months, so that's 3* 7 = 21 hours per week about 8 months of the year. Per week, that was 21* 2.3 = *48.3 m^3 of gas*, which is 21*25.3 = *531.3 kWh* of gas, which is 531.3kWh  * €0.06 = *€31.88 per week. *For 8 months a year, that's €31.88 per week * 32 weeks = *€1,020.16 per year to heat the house with gas.
> *
> ...



You say it has done away with 98% of your gas heating and saving you €1,020 but you have not stated how much it is costing you in solid fuel to burn.

Hard wood dried to about 20% moisture content has about 3.5kw of energy per kg in it and if you are using a modern stove with an efficiency of approx 75%, that's about 2.6kw per kg. Dry hardwood to that moisture content is not cheap and usually at a much higher MC.

Solid fuels also receive carbon taxes and I've come across clients spending €60 per week on coal to heat a house.

Don't get me wrong, I'm certainly not against solid fuel, but it has got its limitations and it is certainly not cheap, unless you have a free supply. It also takes a good amount of work to load, clean and re-stock.

If your gas boiler and solid fuel back boiler share the same water, especially when you say you have a high efficiency boiler, the heat exchanger of the gas boiler is extremely restrictive and will without doubt be negatively affected by the solid fuel side. Be also aware many manufacturers will not stand over there warranty when plumbed this way.

If you are using 2.3m3 of gas that is 24.8kw per hour gross, so your net heat input is 22.8kwh. If your boiler is a condenser, it will be SEDBUK 90% efficient so your system demand is therefore 20.5kw per hour. To satisfy that demand with your solid fuel wood burner you would need to burn approx 7.9kg of hardwood timber. At an average cost of €0.38 per kg, that costs €3.00 per hour to run your solid fuel!!!

Compared to your calculated €1.62 per hour for gas, it's a no-brainer, unless you are heating your rads to heat to a much lower temperature or your are purchasing the hardwood much cheaper, etc.


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## Leo (17 Sep 2015)

You'd need to be on a bulk-delivered pellet boiler for wood to become more cost effective than oil or gas per delivered kWh.


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