Welcome! Here are the website rules, as well as some tips for using this forum.

# How does this hydronic system look with baseboards and manifold?

Member Posts: 37
edited August 9

Trying to run water @ 150f, trying to have the manifold at the basement and run the 3/4" pex circuit throughout the first floor ceiling. Each circuit should run @ 4gpm.

Does it look good ?

What should be max length per circuit ? Should I count the length to determine pressure loss?

• Member Posts: 400

I see a total of 120 feet of baseboard, that's about 50,000 BTU/hr at 150F. With return water at 130F that's 5 GPM for everything; with return water at 140F that's 10 GPM. (BTU always equals GPM*temperature drop*500).

The longest radiators are 18 feet, that's 7200 BTU/hr. With a 10F drop that's 1.4 GPM, with a 20F drop it's 0.7 GPM. I'd go with the higher temperature drop so you can go with 1/2" pipe throughout, it's easier.

Is your plan to have each room on its own zone with its own thermostat? Because if not I don't see any point to a manifold. Run two 1" pipes up from the basement and the length of the floor, then have a tee for each room. Once you get past the first couple of radiators you can drop down to 3/4" which will save a bit of money.

You need to have some sort of control on the flow to each room. Since you haven't done a heat loss calculation I'd recommend something thermostat, either a zone valve or a TRV (thermostatic radiator valve).

• Member Posts: 37

I want to have a manifold because I can regulate the flow more in some hot and cold areas of the house to increase or decrease the output.

I would reduce my baseboards to 1/2", If i only need 1.4 gpm per circuit then you right I don't need the 3/4" pex. But I will try to run it at 2 gpm per circuit, therefore I can obtain the most output and hotter delta T.

Should I count the length of each circuit in the manifold, and also count the length of the supply for the manifold to know the pressure drop ?

• Member Posts: 2,768

I would run the 1/2" tubing as suggested by DCContrarian and run @ 1 GPm per unit . The Delta T will be what the DeltaT will be but each unit will have the same water temp thus making a 1 zone system more comfortable and efficient for the longest part of the heating season . You can always still adjust as you suggest later . See chart , https://ocsind.com/wp-content/uploads/2016/03/15981-OCS-Catalog.Updated15-3.pdf

You didn't get what you didn't pay for and it will never be what you thought it would .
Langans Plumbing & Heating LLC
732-751-1560
Serving most of New Jersey, Eastern Pa .
Consultation, Design & Installation anywhere
Rich McGrath 732-581-3833
• Member Posts: 400

Let me try to put into words what it means for a heating system to be "efficient." It means that every part of the heated area is at a comfortable temperature, and that is done at the lowest possible cost. The cost has two parts — the initial cost of the equipment, and the operating cost over the lifetime of the equipment.

For a given system, the only difference in the operating cost is going to be if you have to overheat part of the space to make another part of the space comfortable, that heat is wasted.

Usually, the way a heating system is designed is that you go through the rooms in the building and for each room you figure out how much heat that room needs, then you add up all the rooms to get the total heat for the building. This method has two benefits. First, it maximizes comfort and efficiency, with each room getting the amount of heat it needs. Second, it minimizes the initial cost, as you're not buying more equipment than you need.

If every part of the building responds similarly to changes in outdoor weather, then a system that is sized this way can be controlled with a single thermostat, which further minimizes initial cost. However, if the heating load on different parts of the building vary depending on where the sun is or how the wind is blowing, the only way to achieve comfort is to divide the space up into zones and have a separate thermostat for each zone. In general you try to minimize the number of zones, because the cost of an additional zone is significant and with a lot of zones you have to work the design to make sure that it works with zero zones, one zone or all zones calling for heat.

In general with hydronics there is no penalty for oversizing equipment, other than the additional equipment cost. If a room-by-room heat loss calculation is not possible for some reason, it would be possible to design a system where every room is its own zone and controlled by its own thermostat. So long as the radiator in each room is at least large enough for the coldest days such a system would provide excellent comfort, and it would do so at minimum operating cost, never producing any unnecessary heat.

In general, using balancing valves alone to control the heat output of radiators is not effective, I'll do another post to explain why.

• Member Posts: 400

Why are balancing valves generally not effective?

The problem is that heat output versus flow is not linear, large changes in flow result in small changes in output.

Imagine a baseboard radiator that is 12 feet long. With water supplied at 150F, at 1 gpm, that radiator will produce about 10,000 BTU/hour. What flow would be necessary to cut the heat output in half?

The heat transfer of the water is always equal to the flow times the temperature drop times 500. So if the heat output is 10,000 BTU/hour and the flow is 1 gpm, the temperature drop has to be 20F. So the water is entering at 150F and leaving at 130F, the average temperature of the radiator is 140F. The output of the radiator is proportional to the difference between room temperature and radiator temperature. If the room is at 70F there is a 70F difference between the radiator and the room. To cut the output in half you'd have to cut the difference to 35F, or an average temperature of 105F. The water can never leave colder than room temperature, the average of 150F and 70F is 110F, so your water would be exiting at 70F. That's a drop of 80F, if the output is half — 5,000 BTU/hr — that works out to a flow of 0.125 GPM.

That's a trickle. If you've ever tried to adjust a garden hose to give a trickle of water, you know how hard it is to get an even low flow.

What if you wanted to double the heat output? You'd need to get the temperature difference to 140F above room temperature, or 210F. You can't do that with 150F source water. The most you could ever do with 150F water is get the average temperature of the radiator to 150F, which would give you an output of 11,429. That's the theoretical limit, but it's not achievable because it would require infinite flow. But let's say you wanted 99% of that, or 11,314. That would require an average temperature of 149.2F, or an exit temperature of 148.4F, a drop of 1.6F. That would require a flow of 14 GPM. So to get an increase of 14% you have to increase the flow by 1300%!

Balancing valve only work when the radiators are already very close to what is needed and you want to make minor adjustments in output. Even then, if you have a multi-zone system where the water pressure varies depending on how many zones are calling for heat they can give unpredictable results. If you have radiators that are grossly mis-sized or disproportional balancing valves aren't going to solve that. The only solution there is zoning, either with zone valves or thermostatic valves on each radiator.

• Member Posts: 22,655

Pressure independent, dynamic balance valves are commonly used on systems where you always want a specific flow, regardless of the circs changing output as zones open and close.

PICV pressure independent control valve is a valve that is a zone valve, pressure independent and also adjustable, commonly used in coil kits on air handlers.

Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 37

Thanks for your efficiency explanation @DCContrarian

Yes @hot_rod dynamic valves set certain gpm flow limit through pipes. That was my idea of using that to control the flow through each baseboard circuit because I have different size baseboards. However, I use a manifold that can control the flow through each circuit. I didn't do a heat loss calculation, therefore if one zone need less heat or more heat I will close and open the flow regulator of certain circuits. That is why i choose the manifold even thought it is more expensive, but it would gave me little more control over the output. I also choose long baseboards and low hot water temp, so I can also have more control over the system, in case I have to increase the temperature if needed. The initial cost would be higher but will give me insight knowledge for the remain floors. Then I would choose things more effective.

Thanks you so much for your explanation and suggestion guys. I am still open for suggestions and comments, don't hesitate to comment. I am installing the manifold, to then install the baseboard and circuits. I will keep you update it. Thanks so much I appreciate it.

• Member Posts: 37

QUESTION @hot_rod, @DCContrarian, @Rich_49

Can I make my return through baseboard enclosure using pex ? or you don't recommended it ?

Something like this but instead of copper in the enclosure it would be pex ?

• Member Posts: 400

Yes, but PEX is a little more delicate and less rigid than copper. You might need to give it a bit more support and protect it from rubbing on the metal brackets.

• Member Posts: 37

Thanks @DCContrarian

I'm considering putting tape on the support/bracket/enclosure of my baseboard so that the return rests on the tape instead of direct contact with the metal.

This way of return could cause any noise? Could the baseboard fins damage or melt the pipe? Is it normal to bring pex as a return in this way?

• Member Posts: 22,655

The pex will need to be able to expand, maybe arc up in the enclosure, and large holes through the floor so it can move as it heats and cools.

If the pex comes in contact with the fins it may squeak.

While not as pretty, but you could run the pex below the fins to avoid rubbing?

Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 400

A 10 foot piece of Pex will expand about 1" with a 100F increase in temperature, about nine times as much as copper.