Ok to mix 2-pipe and 1-pipe in same house?

[drongo]

Hi

I'm having a new boiler installed on my old 1-pipe system. Plumber recommends converting to 2-pipe system. Ok but some of the pipes are under a tiled floor I don't want pulled up. So plumber says we'll just convert the rest to two-pipe and leave those on single pipe.

I understand the benefits of two-pipe system. But is it OK to mix them like this? Can it be properly balanced?

Has anybody successfully done it?

Tom

 

[kevplumb]

nothing wrong with a one pipe system if its done correctly

if you mix it balancing should be fun

 

[doitall]

Would you please explain the benefits.

Unfortunately you don't tell us anything about the size or type of system.

To answer the question, Yes you should be ably to mix and match, provided the installer knows what he's doing, without any problems.

 

[simond]

If your old one pipe worked ok with the old boiler .........I would have to ask what benefit to anyone there would be in changing the rest of the property to two pipe.

Some heating engineers are frightened of one pipe and always recommend to rip it out. Be wary of these fellows, they tend to be inexperienced.

 

[bengasman]

...Be wary of these fellows, they tend to be inexperienced.

Been called many things over the past few years, but never inexperienced.
A one pipe system can work, even with a steamer. However, I doubt that there is a single one-pipe system in the country that works better in terms of response, and efficiency then a properly piped up two-pipe system.
And then there is the matter of cleaning a one-pipe system.

You can not mix one and two pipe systems on one boiler without seriously compromising the response and/or efficiency.

Thank whoever suggested doing it half and half for his time, and find somebody else; the man is a cowboy.

 

[heatingman]

The answer to your question is "no you cant mix a 1 & 2 pipe system, different beasts that work on different principles. Nothing wrong with a condense on a 1 pipe, assuming any extra rads are connected and piped following 1 pipe proccedures. Bit of a rascal to clean a 1 piper.

 

[gassafeman]

I have yet to find a boiler that wont suit a one pipe system.

Leave the pipework alone. I DS40 a one pipe system. Powerflushing works but gawd it is hard work.

Paul

 

[drongo]

Would you please explain the benefits.

Unfortunately you don't tell us anything about the size or type of system.

To answer the question, Yes you should be ably to mix and match, provided the installer knows what he's doing, without any problems.

Thanks for the question, doitall. You made me think. Which is usually a good thing. Here's the system:

It's an old semi. Narrow with very tall rooms. I have 10 radiators and a towel rail. The boiler's in the cellar. There's a single attic room with one radiator, 4 plus towel rail on the 1st floor and 5 on the ground floor. The boiler is old and expensive to run and maintain. That's why I'm getting it replaced. I'm also getting TRV's fitted on most of the rads. It's an open vented system.

When the boiler fires up the first radiators in the loop get hot fast and the last ones take half an hour or so to get hot - although once they get hot they're fine. I believe that one benefit of the 2-pipe system is that you don't get this problem of some radiators heating up much faster than others.

The plumber told me that modern "efficient" boilers work more "efficiently" with a 2-pipe system. Although I must say I thought that they use the temperature difference between the outward and return flow, and with a one-pipe system I would expect that difference to be greater, so wouldn't they be more efficient in a one-pipe set up?

I've discussed zoning by converting the pipework to "S plan plus" (??) and having separate controls for ground and first floors. This seems like a good idea because the radiators would heat up much faster using only one zone and also we wouldn't be sending hot water all round the house when we don't need to.

Most people recommend converting the whole house to 2-pipe. But that's not practical at the moment because I would have to replace some tiled floors. However, I have been recommended to convert some rads to 2-pipe where that is practical and I'm unsure about that. Not least because of the difficulty with balancing the system - especially where the use of TRVs is going to cause the load to change over time and I don't know if it will still be in balance when the load changes if some of the rads are on 2-pipe and some on a single pipe.

Anyhow. Any thoughts or experience with a mixed system would be very welcome.

Tom

 

[doitall]

...Be wary of these fellows, they tend to be inexperienced.

Been called many things over the past few years, but never inexperienced.

You can not mix one and two pipe systems on one boiler without seriously compromising the response and/or efficiency.

Thank whoever suggested doing it half and half for his time, and find somebody else; the man is a cowboy.

That's complete horlicks Ben and heatingman, and I'm really surprised Ben came up with a comment like that.

It was common practice to run a high level flow and return pipe through the building, and drop a single pipe to low level and around the skirting, and return several rooms later back into the return.

 

[bengasman]

... Yes you should be ably to mix and match, provided the installer knows what he's doing, without any problems.

Does that include a way of setting the mixed system up in such a way that you maintain your 20 degree drop (more or less, say within 2 or 3 degrees), regardless of which, and how many rads are on or off?
Doing it on a "normal" system is hard enough, I have tried it once on a mixed system, and got nowhere.

 

[doitall]

Drongo,

Provided you have balancing valves on the return legs of the circuits before they are common you should have no problem whatsoever in mixing a single and two pipe system.

What the doubters fail to recognise is, that every cylinder is piped up with a one pipe loop.

One disadvantage is the TRV's must be suitable for a one pipe system, and are twice the price of the normal TRV's

 

[Norcon]

Would you please explain the benefits.

Don't you know then?

 

[bengasman]

What the doubters fail to recognise is, that every cylinder is piped up with a one pipe loop.

Provided it has a valve in it that allows you balance it, it is no different from a spur from the main flow and return on a 2 pipe system that feeds part of the rads, so does not create a problem. If you draw a diagram of a 2 pipe system, it is just another heating load on the flow and return.
In fact, a cylinder which is fed by the flow pipe, and exits in the return pipe, is a 2 pipe system unless there is a bridge near the cylinder connecting the flow and return.

 

[doitall]

... Yes you should be ably to mix and match, provided the installer knows what he's doing, without any problems.

Does that include a way of setting the mixed system up in such a way that you maintain your 20 degree drop (more or less, say within 2 or 3 degrees), regardless of which, and how many rads are on or off?
Doing it on a "normal" system is hard enough, I have tried it once on a mixed system, and got nowhere.

On any system the 20deg difference will go out the window at some stage, it's all about boiler temperature and heat lose in the radiators.

On a larger system we would use a DRV and control stations to measure and balance the flow rates in each circuit, but certainly not necessary in a small domestic.

 

[doitall]

Would you please explain the benefits.

Don't you know then?

There isn't any, but I'm open to your opinion.