Thread: Instantaneous Gas Hot Water & LPG

Originally Posted by ian

I thought that is what I said It was definitely what I intended to convey.

liquid withdrawal for high energy requirements -- e.g. a car, instantaneous hot water
gas vapour for low energy requirements -- e.g. cooking

How can it be different when the same bottle and gas line is feeding both / multiple appliances?

Originally Posted by Beardy

How can it be different when the same bottle and gas line is feeding both / multiple appliances?

as I understand LPG systems, there are two types
1. vapour is drawn from the top of the LPG tank -- e.g. for a bar-b-que -- and passes through a largish hose to reach the appliance.
2. liquid (under pressure) is drawn from the bottom of the tank and passes through a small tube to reach the device -- car engine or water heater. Liquid withdrawal relies on a tube inserted to access the liquid at the bottom of the LPG tank.


as far as I know you won't find both systems on the same LPG cylinder. But, hey, I could be wrong.

LPG vapour (gas) is what is needed and burned through every household gas appliance.
LPG liquid is what a car requires and the big thingy on the carburettor puts what is needed into the engine to make it work. (As you can tell automotive is not my field)

so the gas bottle that you connect to your house (45kg or bulk bottles ) have the tap on the top and draw the vapour off to burn. Same goes for a 9kg BBQ bottle, tap on top draws vapour to burn and yes you can connect these to the house as it is same connection.

LPG bottle the shop uses to fill your bottle has tap on top but inside is a tube that runs to the bottom which draws the liquid into your bottle. When filling the ‘filler’ undoes a bleed screw on the side of your tap to let air/vapour escape. When white gas comes out the bleed screw this is liquid turning to gas and your bottle is full again.

LPG bottle a fork lift uses is on its side and when put on forklift it has a gauge that is in the up/top position there is a tube inside that runs to the “bottom” to withdraw liquid.

LPG bottle in a car is sideways (so it fits easier) also has inside a tube which draws liquid from the bottom.

car and fork lift bottles have their own unique threaded connections so people do not connect car bottles to houses and vice versa.

theoretical: if you turn a House 45kg gas bottle upside down (and have all the right connections) you can fill your BBQ bottle. Don’t try this at home. I think I was told that the liquid comes out at minus 35 degrees and if you fill enough gas bottles without gloves on you will get burned and it hurts like hell and yes once is enough.

cheers

when you boil the kettle and pour it over your BBQ bottle, you run your finger from bottom to top to see how full your bottle is. What you are doing is ‘feeling’ how much liquid there is left. Finger feels the cold at bottom (liquid area) when your finger starts to feel warm this is the area where vapour starts. Note when the bottle is nearly empty there is not a great temperature difference as not enough liquid to cool through bottle. On a nearly full bottle sometimes no finger required as you can see condensation line on the bottle.

When my instant heater was installed, the plumber had to install a new line from the LPG Vapour bottles which is bigger, normal line is 1/2” or 12mm, new line is 3/4” or 19mm.

Originally Posted by ian

as I understand LPG systems, there are two types
1. vapour is drawn from the top of the LPG tank -- e.g. for a bar-b-que -- and passes through a largish hose to reach the appliance.
2. liquid (under pressure) is drawn from the bottom of the tank and passes through a small tube to reach the device -- car engine or water heater. Liquid withdrawal relies on a tube inserted to access the liquid at the bottom of the LPG tank.


as far as I know you won't find both systems on the same LPG cylinder. But, hey, I could be wrong.

I haven’t seen anything like that here
They are plumbed the same way as being on natural gas except your pipework goes back to your chosen bottle location.
There is only one line running from the bottles and you branch off to whatever appliance you choose to connect. The pipework needs to still be sized accordingly to ensure sufficient gas flow for the said appliance

Originally Posted by ian

Chris
If you are worried about power interruptions at the house, Bosch do an instantaneous unit that relies on water flow to ignite the burner. Might be an option for you. HydroPower | Hot Water | Products |
I'm sure other makers have similar systems

This is the system I use and never had a problem. We have had lpg stove and instant heater for over 40 years and the savings are definitely worth going this way.

I alway thought solar with gas instant hot water system in series made sense - to me. If solar hot water is not hot enough, gets a bit of extra heat added as it passes through the instant hot water system. Not using hot water, not using gas either.

when I did some research a few years ago, solar systems had mostly electric boosters to keep the hot water hot if solar not getting it to temperature. Not using hot water, electric booster still keeping water in tank hot I.e using electricity just in case I need hot water.

maybe I am missing something, but seemed like a simple system.

Here is a pic of my gas setup, you can see the 19mm gas supply line in the centre under the regulator going to the various appliances

Originally Posted by ian

Chris
If you are worried about power interruptions at the house, Bosch do an instantaneous unit that relies on water flow to ignite the burner. Might be an option for you. HydroPower | Hot Water | Products |
I'm sure other makers have similar systems

I have read some pretty poor reviews of the Bosch heaters but there must be happy owners as well.

There is one other thing that you need to consider. Should you ever get natural gas where you are, the water heater, space heater and kitchen will require different a orifice. Smaller due to more energy being in the natural gas. it is just a little brass thing that is very inexpensive. However if your water heater doesn't have an interchangeable orifice you'll have to change the the whole unit.

Originally Posted by rrich

There is one other thing that you need to consider. Should you ever get natural gas where you are, the water heater, space heater and kitchen will require different a orifice. Smaller due to more energy being in the natural gas. it is just a little brass thing that is very inexpensive. However if your water heater doesn't have an interchangeable orifice you'll have to change the the whole unit.

What you say is true, the two fuels use different sized orrifices. Here in Oz a lot of appliances come from the distributor configured for one fuel but with a set of orrifices for the alternate fuel included so that the unit is convertible in the field. If the purchaser is lucky, the installer leaves the alternate set in the appliance housing (room heater or HWS) or hands them over to the owner, so they are available if a conversion is required at a later time. I get the feeling that for the east coat of Oz, the gas supply situation fairly stable, i.e. the only expansion of the natural gas network will be in new estates being developed close to existing NG serviced areas, and ares removed from the NG network will continue with LPG.

Originally Posted by Beardy

Here is a pic of my gas setup, you can see the 19mm gas supply line in the centre under the regulator going to the various appliances

Supply line size is a function of what your potential peak load is. If you are running gas cooking or heating as well as HWS you need larger feed pipes to maintain appropriate flow and pressure to all appliances should they all need to operate at the same time. Cook would not be happy if the oven goes out because someone wants some hot water to wash their hand, or the gas heater kicks in.

DJ mentioned that they had to upgrade his feed pipes when he converted to instantaneous gas, that in itself suggests that the plumbing was in place to supply other appliances and was sized to suit that demand, but needed updating for the additional demand.

Originally Posted by malb

Supply line size is a function of what your potential peak load is. If you are running gas cooking or heating as well as HWS you need larger feed pipes to maintain appropriate flow and pressure to all appliances should they all need to operate at the same time. Cook would not be happy if the oven goes out because someone wants some hot water to wash their hand, or the gas heater kicks in.

DJ mentioned that they had to upgrade his feed pipes when he converted to instantaneous gas, that in itself suggests that the plumbing was in place to supply other appliances and was sized to suit that demand, but needed updating for the additional demand.

19mm is the standard for most installations, when we have fitted two instant HWU on a house we have had to upgrade the line to 25mm

Do you have 3 phase power? Steble Eltron do a continuous flow unit which is the ducks guts. No flue, indoor install, no bund, uses mil amps when not running, can service more than one point.

I had one installed in my creative space when I bought my premises. The unit takes up next to no space. About 600 x 200 x 100. I have it mounted in the cupboard beside the bathroom.

well worth looking at me thinks.