After 7 years of freezing my backside off through the winter I would like to try to make use of the back boiler on my open (coal/wood) fire and run 5 very small radiators (3 small bedrooms, bathroom, landing) off it. I am looking for advice about how I go about this especially I have a none existent budget! However I do have lots of diy experience having restored the house from a shell and done the rest of the plumbing and I'm happy to get an expert in to check everything over but I need to figure out what I would need and what's possible. I've never laid sight on what sits behind the fire but its sufficient to provide piping hot baths when the fires been running for a bit. The tank it feeds to is a big old copper thing that I thought about replacing when I first bought the place but I'm so glad I didn't as it was god send when the money ran out! Anyone with experience in this area any help most appreciated!
Havn't seen such a system for decades. IME they were usually plumbed in iron piping (looks a bit like scaffold tube) which are a PITA to break into and modify. But then I've only seen them with galvanised hot water tanks. If yours is plumbed in (say) 28 mm copper (more likely to be imperial, come to think of it) then in principle you could break into that. But being a direct system they will want to "fur" up. The other problem I can see is that open fires are not really very efficient. I think changing to a closed stove might be my priority: you will get much more useful heat for a given amount of fuel, and that should spread upstairs.
The OP lacks funds, I'd look at getting the existing system going. It should use very wide piping with gravity circulation, so I'd look for the header tank for the heating, see if its still present, and if so fill it a bit cautiously, it may work.
There are a few no cost ways to insulate houses too, see our wiki's Insulation article
There are two pipes running from the back boiler to the hot cylinder. You tee into both of them. Take a tee'd feed from top one to a pump, thence to the feed side of the rads in parallel. The return pipe from the rads in parallel then comes back and tees into the colder, bottom pipe that runs from the tank to the back boiler. Assuming the hot cylinder is an indirect one, there should be a header tank to keep the basic circulating water topped up. OTOH, It might be direct - that will still work, but it will tend to scale up more much more and direct systems, even for such basic installations as you have are fairly rare and have been for decades. The pump is controlled by a pipestat mounted on the top pipe from the back boiler to the hot cylinder - when the temp hits 60degC, the pump takes over and circulates water through the rads; when the temp drops, the pump stops, until the next time. It's a fairly effective system but primitive and not at all efficient as most of your expensive heat is going up the chimney, but it does work. You can maximise its effectiveness by insulating as best you can on the money you have. Try to find the cheap rockwool and glassfibre deals for attic insulation and use fillings of those for drylining your walls after you've done your attic.
I suggest a first step would be to calculate the output you're getting from the back boiler and then work out how many radiators that will support.
If you measure the dimensions of the immersion tank you can calculate how much water it holds. If you ignore the domed top bit and just calculate the volume of the cylindrical section you won't be far out by the time the volume of the heating coil pipework inside has been subtracted. For example my 450mm x 1200 mm domed top unit is marked as holding 162 litres. The straight bit measures 102 cm tall with about 17 cm of domed top above that.
Cylinder area is 45 x 45 x pi / 4 = 1590 sq cm
Volume of straight bit is 1590 x 102 = 162,180 = 162 litres so pretty much spot bollock on.
Now you need to get the fire going fully which may take an hour or more, drain off the hot water that has accumulated so far and take the temperature of the cold water that the tank is now full off and chart the temperature rise as this heats up. An infra-red thermometer would be useful. From this you can calculate the kW/hour output into the tank.
Every Kw will raise the temperature of 86 litres of water by 10 degrees C in an hour. So if for example your tank holds 150 litres and the average temperature rises by 20c in an hour your back boiler is pumping out 150/86 x
20 / 10 = 3.5 kW/hr.
Remember the tank will get hot at the top first so just taking a temperature measurement here will fool you. You need the average temp of the whole tank. That might take a bit of guesswork or you can leave it until the whole thing is popping and blowing off steam when it's safe to say all the water is close to boiling. Even taking precautions you'll probably over estimate the ouput of the back boiler somewhat.
You can estimate the radiator kW/hr usage from this chart
formatting link
a smallish single panel rad will use about 1 kW/hr and you probably want twice that in an average room to achieve much in cold weather. That of course depends on how well the house is insulated etc.
I suspect you'll find the back boiler can't run many rads because most of the heat goes up the chimney. I doubt if it'll be more than 3 to 4 kW/hrs output which might give you a couple of decent sized rads but it's not going to make much impact on the entire house.
Still, it gives you a fun exercise to do with a thermometer and a calculator one day.
Just as an afterthought, and I know how Heath Robinsonesque this will sound but one way of avoiding wasting all that hot water the back boiler creates and often vents off as steam when the immersion tank gets too hot might be this.
Get yourself a few of those 25 litre plastic, or even metal, chemical cans that businesses get their solvents, oil and other stuff in. You'll find dozens being chucked in any industrial park if you ask around. One of those full of hot water is storing about 2 kW hours of heat. About the same as a big rad running flat out for an hour. A bit like a big hot water bottle but for the room rather than the bed. A couple of those will take the chill off a room for a few hours although lifting a full one is a struggle. Half full ones would be easier.
It's no long term solution but it might let you see just how much spare hot water you generate and if radiators and all the associated plumbing might make any financial sense. At least it's free.
If your back boiler is a square thing about 200mm with a tunnel under it, it will be copper and originally intended to heat hot water only with a direct cylinder (no coil/heat exchanger). It will be far far to small to run more than a single radiator and is probably knackered by now anyway. Definately not worth bothering about. If you want wood fired heating yo uneed a woodburning stove, you can get them with waterjacket for heating.
There wereonce larger all-steel boilers that went in thefireback but they were absolute crap even when new.
Open fires are very bad news when it comes to heating. The reason you are freezing your arse off is that the fire is drawing cold air into the house. What you need is a room sealed woodburning stove that draws combustion air from outside. & hence generates no draughts. This sort of thing.
I'm seeing a lot of suggestions based on assumptions. We'd need to know what bikergrrl actually has first. One thing will always be true though: back boilers have quite limited heat output.
I think you have to allow for the situation in which the fire is burning but the pump isn't running. Even though that might not be intentional. Which does indeed mean larger pipes.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.