Flow- Vent- Feed -Pump

[desktop987456]

Boiler with pump but no exp vessel is a new one on me, but we live and learn!

I can send a picture if you like, trust me it is without an expansion vessel, its a boiler from stoneage! It gets the job done of heating the house but with energy prices it is very in efficient.

I would put the cold feed on the return pipe

What is the advantage of having feed on return pipe, since I inted to install filter on return as well. Some posts I have read lately talk about having pump on return for heat only boiler, it gets very confusing. What's the best practice for feed and pump; flow or return?

If you use a separate vent

As Madrab said that I don't know what I have; sealed or OV as I thought of this system as OV so I bought a OV boiler (but PRV,NRV and no vent tell a different story). I think it would make sense to stick to OV and do the pipework and installation as per OV standard which is Vent,Feed, pump.
Can an OV boiler be used in a sealed system (by installing a exp vessel)?

The balcony where boiler will be installed is only 7 feet high so having min vent length of 40" from boiler + 24" boiler height would make me shift boiler just 1.5ft from floor. Are these lengths a must for hydronics and safety. Can these lengths be slightly less than this e.g why feed has a minimum distance of 15" from flow line?

if you're thinking of installing a HW cylinder in future

Once CH is up and running and I get the required efficiency gains from boiler, I will definitely do it, Thanks for common return concept to boiler.

 

[fixitflav]

I can send a picture if you like, trust me it is without an expansion vessel,

Don't need to do that, I wasn't suggesting you were telling porkies! Just that I haven't seen one, but there's loads of things I haven't seen

What is the advantage of having feed on return pipe,

My comment was in connection with a boiler with built-in pump. It's always best to put the cold feed (your system positive pressure point) near the pump suction to ensure the pressure doesn't drop below atmospheric at any point, with risk of air being drawn in.

Some posts I have read lately talk about having pump on return for heat only boiler, it gets very confusing. What's the best practice for feed and pump; flow or return?

Pump on the flow used to be the rule I believe, but there are pros and cons either way. On the flow, vent just after
boiler gives better chance of air release, mainly from the boiler on first use. But after the system has settled down there should be negligible amount anyway. On the return the pump sees lower temperature, which could give longer life. Also the layout of the house might affect the choice.
My filter is on the return pipe, but AFAIK it can be on either.

As Madrab said that I don't know what I have; sealed or OV as I thought of this system as OV so I bought a OV boiler. Can an OV boiler be used in a sealed system (by installing a exp vessel)?

Some prefer OV, some pressurised. I prefer OV. I'd be surprised if your OV boiler can't be used pressurised, they're usually good for the pressure, but I'd check with the supplier. There can be problems changing an existing OV system to pressurised as the higher pressure might cause leaks.

The balcony where boiler will be installed is only 7 feet high so having min vent length of 40" from boiler + 24" boiler height would make me shift boiler just 1.5ft from floor. Are these lengths a must for hydronics and safety.

Your sketch looks OK to me. Perhaps Madrab will comment. The top of the vent loop must be minimum 18" above the F/E tank water level, probably is but can't be sure from the dimensions given.

Can these lengths be slightly less than this e.g why feed has a minimum distance of 15" from flow line?

My boiler manual says minimum 18" from the flow pipe to the F/E tank water level (roughly same as your 15" to tank bottom) so I'd stick with that unless your boiler wants something different.

 

[desktop987456]

My boiler manual says minimum 18" from the flow pipe to the F/E tank water level (roughly same as your 15" to tank bottom) so I'd stick with that unless your boiler wants something different.

Got the dimensions from net for OV.

 

[fixitflav]

Got the dimensions from net for OV.

Those dimensions don't tie down the important one - 18" minimum from water level to top of loop. Not enough care taken IMO! But if you ensure you meet the 18" you could do it that way. Though I don't see any need to use 45° and 90° bends as shown. An inverted U as in your earlier post would be fine.

 

[Madrab]

Ah ok, it's the compact. Can I ask, is this boiler rated for the US, that should be on the data plate. Not sure what the differences may be in the US with NG etc. I know Viessmann are quite specific about where their boilers can be used.

I have read lately talk about having pump on return for heat only boiler

don't think about putting the pump on the return, more where the boiler will be placed on the circuit, if you see what I mean. There are different schools of though where the best place to put the boiler is. Some say a pump should 'pull' from the boiler with the more modern HEX's, other say it is better on the return to reduce heat stress as it's cooler. Design standards with a Y plan usually have the pump pulling from the boiler flow and then output from the pump pushes towards the 3 port. The key is there is nothing between the boiler and pump other than the feed and expansion, to ensure the system is balanced properly. There is also the option of installing an air separator set up or 'H' to reduce pumping over risks.

As suggested, the 100-W can probably be run OV or be sealed yes but best to check with Viessmann. The system would also need pressure tested to ensure it can cope with sealed system pressures, if that was the direction.

Min height F&E tank to system is to provide min head allowing the system to be fed properly from the cistern, vent min height above the cistern to stop pumping over and allow for expansion. Max distance between feed and vent is to ensure pressure differentials are kept to a min, again to avoid pumping over/air drawn in/reverse circulation back up into the cistern.

 

[Johntheo5]

Do it this way, remove the "H",no problems with pump over etc

 

[Madrab]

Do it this way, remove the "H",no more problems.

View attachment 312898

Combined F+V , not everyone agrees that it's the safest approach as it can interfere with the safety vent. Also allows expansion back into the cistern when ideally that should be handled by the vent. Needs to be designed in quite specifically IMO. A properly designed OV system shouldn't need a combined F&V IMO.

 

[desktop987456]

Ah ok, it's the compact. Can I ask, is this boiler rated for

I am going to find out after installation. LPG is the back up option in case there is a difference in pressure.
I am grateful to you for your time and suggestions and Fixitflav, you have clarified a lot of things which were bothering me.

- Will put pump on flow (see pic);
- it will be OV system with separate vent and feed.

Have I got this right in terms of min 6" or 150mm gap between the pipes?

A pipe from boiler flow will serve as vent as per spec 40" high over F&E cistern.
Last thing I want to ask is what would be the layout of Feed into this pipe?

 

[Madrab]

min 6" or 150mm gap between the pipes?

Max between, not min, keeps pressure differentials to a min.

Feed could be cut into the middle of that pipe just before the pump inlet but I would provide say another 100mm of pipe from the feed to the pump inlet to minimise direct suction/draw.

As an aside to this have you had any more thought about the actual rad system design, you need to consider resistance through the system/rads/valves etc from that then pump settings, balancing etc, there's a lot to consider and design into it to avoid basic issues like air draw, pumping over etc. That's why I mentioned about looking at the actual flow and return pipe runs etc.

 

[Harry Bloomfield]

My filter is on the return pipe, but AFAIK it can be on either.

Better on the return and just before the boiler - Idea is to prevent crud getting into the narrow boiler passages, the crud is from the radiators, so therefore in the best position to filter that out.

 

[desktop987456]

As an aside to this have you had any more thought about the actual rad system design, you need to consider resistance through the system/rads/valves etc from that then pump settings, balancing etc, there's a lot to consider and design into it to avoid basic issues like air draw, pumping over etc. That's why I mentioned about looking at the actual flow and return pipe runs etc.

Sorry, max 150mm.
The pipework and rads are in place and central heating worked with previous boiler fine (with integral pump; it was Grundfos with 5m head).

I have never used an external pump in my system so this will be first experience. My initial estimates suggest that with 30k btu load the system would be requiring 3gpm or 11lit/min (all theoretical). I would appreciate any pointers or reading material if you can refer.

This Flomasta pump is Delta P pump so is more adjustible to varying heating loads?

 

[desktop987456]

Better on the return and just before the boiler - Idea is to prevent crud getting into the narrow boiler passages, the crud is from the radiators, so therefore in the best position to filter that out.

Thanks, will have it installed on Return just before the boiler; Is there a minimum distance limit or you an place it anywhere?

 

[Harry Bloomfield]

Thanks, will have it installed on Return just before the boiler; Is there a minimum distance limit or you an place it anywhere?

So long as it filters all of the crude out in the return, anywhere in the combined return will do.

 

[fixitflav]

So long as it filters all of the crude out in the return, anywhere in the combined return will do.

Yes better on the return so the crud doesn't go through the boiler and pump before it gets caught.

 

[desktop987456]

Message from Viessmann technical support about height and static head for feed.