Combi Boiler System Installation Help

[John Gayewski]

Yes they all need an expansion tank. I don't remember why it's not pictured. It's been a while since I read all of that.

 

[Reicherb]

Does it matter what loop I put the tank in?

Edit: it looks like it makes no difference.

 

[Sponsor]

 

[Reicherb]

I have looked at the manual numerous times and can't make heads or tails how I connect a 2nd circulator pump. Can you point me in the right direction? The manual is here: https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Weil-Mclain-383-100-030-User-Guide.pdf

Do I need an external relay to control the circulator? In the manual, they reference connecting the circulator for the heat only version of the boiler but seem to make no refence to the combi unit.

 

[John Gayewski]

You need a multi pump controller.

 

[John Gayewski]

There are other ways to wire them in. But it depends on how you want them to come on. Many times you need an external relay.

 

[Reicherb]

Here is what I have planned. Any red flags? Better choices, etc?
https://docs.google.com/spreadsheet...ouid=117999286997451135666&rtpof=true&sd=true

When any zone calls for heat, both the primary and secondary circulators would be on. Correct? Does the pump somehow modulate based on how many zones are calling for heat or is that not necessary?

 

[John Gayewski]

When any zone calls or there is a water demand, the primary pump would come on. The secondary pumps should only come on if the thermostat for that specific zone calls.

Your boiler should have programmable heating curves for different zones. An Outdoor reset can help with boiler run times. Ideally the boiler and pumps would run all of the time for max efficiency, but it doesn't work out like that.

 

[John Gayewski]

Is your pex an oxygen barrier type of pex like hepex?

 

[Reicherb]

When any zone calls or there is a water demand, the primary pump would come on. The secondary pumps should only come on if the thermostat for that specific zone calls.

Your boiler should have programmable heating curves for different zones. An Outdoor reset can help with boiler run times. Ideally the boiler and pumps would run all of the time for max efficiency, but it doesn't work out like that.

You think I should use 3 secondary pumps rather than 1 pump and 3 valves?

It is oxygen barrier pex.

 

[Fitter30]

Heres a boiler pump a d zone controller with dhw priority
https://www.supplyhouse.com/Taco-SR...MI-fOs1q3o8gIVV3xvBB1iSg8UEAQYBCABEgLbhfD_BwE

 

[Reicherb]

Why do I need DHW priority? Isn't that totally separate and controlled by the boiler?

 

[John Gayewski]

You think I should use 3 secondary pumps rather than 1 pump and 3 valves?

It is oxygen barrier pex.

Is just what I would do. Some people don't mind zone valves.

Most trouble shooting websites I see have people complaining in one way or another about zone valves. They are more finicky than pumps. Water hammer, won't close, won't open, won't close all of the way, won't open all of the way.

Circulators are starting to come with cartridges in them that you just change out in the even of a failure.

This is just my preference. Over the life of a 20 year system a circulator might cost $1000 to run. The reliability in my opinion is worth that cost.

 

[Reicherb]

Can you help me make sure I have the correct size circulator in both scenarios? I have 3 zones.
1 zone has six 200' loops of 1/2" pex and 33,000 BTUs of load.
2 zones each have one 200' loop of 1/2" pex and 5,500 BTUs of load.

I've read this over and over and over and can't seem to figure out the correct math. I'm looking for help with both the single circulator and circulator per zone as I'm still pondering that.

 

[John Gayewski]

So the boiler you pick out may have the primary circulator built in. Your primary loop would need to be sized for the total load 44k btu and 4.4 gpm 12 ft of head. Probably 1.25"pipe.

The secondary pump for zone one would need to be sized for 3.3 gpm and 12 ft of head.

Zones 2 and three need less than 1gpm at 12ft of head.

Using the pump curve for the product (pump) you want to buy will tell you the size that will fit each zone.

Your other 2 zones being so small of a heating load with such long loops is odd.

The head only needs to be figured from the longest loop in each zone.

 

[Reicherb]

The zones are very different because it's a barn. The main building is 30'x40' with 6-200ft loops. The other 2 loops are each 10'x20' with 1-200ft loop.

If I use a single pump capable of 4.4gpm and 12ft of head, what happens if only one of the smaller zones is open? The flow won't be too fast correct? Someone previously said to use the Taco 007e but that doesn't appear to be enough head range if I wanted a single pump.

How did you come up with 1.25" for the primary loop?

Thanks.

 

[Reicherb]

The AB-80C says it has an "internal 3-speed Grundfos" I can't for the life of me find a model number. There is a table that references "Grundfos UPS 15-58" Does that seems like what it has? If that is the case, wouldn't that be able to supply the entire system?
https://product-selection.grundfos....rica/ups-15-58-fc-59896341?tab=variant-curves

 

[John Gayewski]

The primary loop just pumps around the primary loop. I put 12 ft of head mistakenly. It doesn't need much power just enough to get around the primary loop and back to and through the boiler. It is beyond likley that the pump supplied with the boiler will do the primary loop no problem.

 

[John Gayewski]

Each size of pex has a limit of how many btus it can supply within the design of pex hydronic systems. 1.25 was just a guess based on most systems sizing.

Looking at some of my design manuals 3/4" pipe would probably get you, but I wouldn't use pipe that small on my primary loop. 1"at the smallest.

 

[Reicherb]

1" is what I was planning. What are your thoughts on copper vs black pipe between the boiler and pex?

If it's not 12' of head, what is it? I was planning to upside the secondary circulator from a Taco 007e to a Taco 0015e3. Do I need the bigger pump?

 

[John Gayewski]

I would use copper. There is less friction loss and it won't rust. I haven't seen many primary secondary systems using black pipe, but people do it.

Your primary loop just needs to pass 4.4gpm with the friction loss of the boiler and the near boiler piping.