I'm trying to install an open hydronic floor heating system to heat a 300 sq ft room in my basement using my existing hot water heater. I followed a plumbing schematic I found online, but it does not work. The pressure gauges in the system are maxed out at 75psi, so the pressure is higher than that. If the pressure reducing valve is on, I get no flow at all and the hot water pressure in my house is reduced. If I turn the pressure reducing valve to bypass, I can get flow of about 0.5 gpm, which is too low and under conditions that are not right for the system. The schematic is posted below. Here are my questions: 1. Is there anything I can do to make this open system work better? 2. Should I give up on the open system and install a heat exchanger? I think this will allow me to drop the pressure in the heating system and maintain the pressure in my house. 3. Is there something else obvious to an expert that I am not seeing or forgetting to ask? Thanks for any help you can give. Mark

There is no pressure reducing valve in that diagram.

What is the pressure at the cold water supply?

If you put a pressure reducing valve in the cold water supply to the tank, you have reduced the pressure of all the hot water plumbing in your house

>I can get flow of about 0.5 gpm

Connect your cold water supply to the inlet of the water heater. You do not want to force incoming cold water to flow through pumps that are turned off. Or at least make sure all the valves are completely open.

Open loop systems are illegal for health reasons. Installing HVAC systems without a permit is also illegal.

Wrong, Open loop systems are legal in many states. example small town Seattle, Washington. Check your local codes for legalities and related permits.
While not a fan of open loop the schematic is ok, Bringing water through the pumps as shown minimizes stagnate water by keeping fresh h2o moving through the system in the off heating season.
As Krom points out schematic shows no pressure reducing valve only a pressure relief, 75 psi is normal on a residential service.
Did you insulate under slab, pipe size, spacing, length? delivered water temp? pump size? Bronze or stainless?
Pumps in right direction? Check valve in the right direction if installed?
Dan

Sad but true Dan.

Thankfully most of us have some smidgen of autonomy and is still the case that most HVAC work is installed without the benefit of a permit. We are licensed for HVAC and plumbing in Minneapolis and St.Paul which qualifies us in all outlying, less regulated, municipalities but enforcement is inconsistent.

License, bonds and insurance are all fine and dandy but no absolute insurance of performance.

I have designed and owned "open" systems, but find them less than optimum and unfortunately attractive to the less-than-careful DIYer. Cheap installation is a poor excuse and all other factors can lead to poor performance and high maintenance. Like codes and permits the cost-benefit of an open system is dependent on the conditions one finds oneself.

Here in Minnesota we are fighting to keep the single-wall heat exchanger in the prospective revised UPC! It will be another couple of decades before the subject of 'open" systems can even be breached.

However, we are installing a multipurpose plumbing/fire sprinkler system this summer in a new home in Minneapolis most certainly a result of heavy lobbying by heavy hitters like Uponor.

I don't think you will see a significant player promoting open systems in the short term by I am consulting with one at the moment. They certainly can be made safe but the current standard, isn't .

Thanks to everyone for your replies. I am convinced to get a heat exchanger and convert my system to an indirect system. I also noticed that I did get a pressure reducing valve instead of a pressure relief valve. Still, with that bypassed, my flow is very low. I insulated under the slab. I'm using a grundfos alpha 15-555 stainless pump to push water through a 3 loop manifold with 3, 100ft loops of 1/2" PEX laid 1 ft apart. Thanks again.

take the pressure reducing valve out of the system completely, even with the lever flipped, they are a big restriction

yes, that's where I would start, remove the PRV, no reason an alpha cant push 3 100' loops of 1/2 pex. might experiment putting the alpha on 3 with lever up on the prv.
Is your alpha stainless,
Dan

Sad but true, open systems are often not illegal in unregulated states where HVAC companies don’t even have to be licensed, bonded and insured to legally operate. Being a licensed, bonded and insured company, we have never designed/installed open systems and never will.  The health risks associated with open systems are well known so we don't advocate or enable the use of open systems either. Consequently, we totally defer to those companies who are not legally bound by regulations to uphold public safety or held accountable for not doing so.  Such companies often operate from unregulated states into other states making enforcement problematic too.  However, it likely isn't very wise for these companies to boost about their open system design/installation experience on public forums where the information is discoverable forever and could be a liability for them should they ever find themselves legally accused of harming someone.

Open loop vs Closed loop conversation again?
Licensed vs unlicensed again?
I hail from Washington state.
Washington requires tradesmen to be licensed and bonded.
Washington permits and inspects open loop system in residential construction.
Washington state's Seattle housing authority in fact has installed thousands of these systems in there projects over the years.
So, while I do not prefer open systems. I design around boilers. Lets not generalize and assume open loop systems are provided by unscrupulous unlicensed fools from unknown places out to part you from your hard earned $.
There are a lot of highly skilled tradesmen that prefer the open loop to a boiler due to cost, maintenance or whatever reason they might have.
A simple 3 loop system as described, no issues, put it on a timer and move on, next.
Dan

Are you licensed, bonded, and insured to design/install hydronic heating systems Dan?

I wouldn’t exactly describe the Seattle Housing Authority as a hydronic heating system best practices role model. They are frequently at the center of homeowner lawsuits which often involve hydronic heating systems and medical issues. For example:

http://www.seattlepi.com/local/article/Homeowners-group-sues-Seattle-Housing-Authority-1268223.php

We find that it is the companies that have the least legal accountability (e.g., NOT licensed, bonded and insured) and that also operate outside their state of jurisdiction are often the biggest advocates and enablers of open hydronic heating systems.

Agreed, it is best not to assume anything when hiring a HVAC company. It is best to carefully check a company’s credentials and references before hiring the company. It is best if the company is actually legally operating in the state in which the hydronic heating system will be designed/installed so you have legal recourse if there are any problems that need to be resolved. Even simply googling a company’s name with problems or complaints in the search box can be quite revealing.

The article you site is from 2008.
At that time and prior, about 2004 my company (BlueRidge Company) was involved with Seattle Housing Authority (SHA) in designing and providing the boilers, radiators, and prefabricated boiler assembly for the forward solution for there next large SHA project High Point (575+ residential units phase 1 and phase 2). It took quite a while and considerable effort but ultimately we (BlueRidge Company) helped SHA realize that a wall mounted boiler providing domestic water on demand isolated via heat exchanger was a superior choice both economically to operate and had greater heat capacity with less potential health issue exposure when compared to there current open loop system. SHA Holly Park project was in full build phase when we started working with design change concepts to there heating. So I am aware of the issues they had, yes. As I understood New Holly development problems (the article you referenced) were largely associated to the use of Kitec pipe failure, possible undersized water heater units as well as a overall bad design using a pump 24/7 to keep water in flow.
To the topic;
Open loop systems are a approved option in may jurisdictions.
Your initial statement was wrong and baseless. Open loops are approved in your humble state of Oregon if I am not mistaken.
Seattle has had its issues with them, yes. This will happen when there are some 5,000 systems installed.
I prefer boilers as stated, but open loops are permitted all over this fine country.
If a person is committed by what ever reason to open loop, do it right. Cycle the water every couple of days, or design so make up h20 flow goes through the heat loops on the way to the water heater keeping water fresh as in this fellows design use potable rated product.

Dan

I have hot water pipes that go to a guest bathroom that doesn't get used for months. I also have a spot where infrequently used pipes sit near a heat duct. It's never been clear to me why this common DHW setup isn't a health problem.

If I were concerned about it, I'd use a pump on a timer to circulate back to a 130-140F water heater. Otherwise a two week summer vacation (warm room temps, no hot water usage) is plenty of time for things to grow.

Right,
Same with the rest of water systems all over the world.
When you add a radiant system, say 2,500-5,000 lin feet of pipe you just increase the odds against you or your client.
So it becomes good design to add timed circulation if you feel you must heat open loop.
Here is a quick description of the problem;

copy/paste source; http://www.legionellatesting.com/
What is Legionella?
The Legionella organism is a gram negative, rod shaped bacterium that can cause pneumonia (Legionnaires' Disease) or a flu like illness (Pontiac fever). It was first identified and recognized as causing disease during the outbreak that occurred in conjunction with the American Legion Convention in Philadelphia in 1976. There are over 40 species of Legionella and 18 of those can cause disease. It is estimated that the species Legionella pneumophila causes most of the infections.

Legionella is a fastidious organism, meaning it has specific growth requirements that need to be met in order for it to survive and grow. Some of these growth requirements are:
Temperature above 68° F
Iron
L Cysteine
Biofilm (particularly protozoans)
Unlike some other bacteria, it can survive at lower dissolved oxygen levels and is somewhat resistant to chlorine disinfection. Certain plastics and organics can provide nutrients for growth. These attributes make our modern day plumbing systems a good habitat for the organism.

Dan

It's also very widespead - approximately 20% of houses (or 40% of houses using electric water heaters) have Legionella (even without open loop hydronic heating). Here they write:

We do not believe disinfecting measures at the domestic level are needed, considering that our retrospective study on pneumonia in residents did not show a relevant evidence of risk in colonized buildings.

But it makes good headlines and plenty of grist for those who insist the sky is falling...

Like lead poisoning; the stars have to line up and the victims qualified with certain risk factors, including compromised immune systems, etc.

Maybe we should say that all buildings with domestic hot water have an "open loop hydronic heating system". It's just very small (a few pipes).

True enough, but this is a significant risk factor for those companies that can be held accountable. When little Billy cries in court that the evil plumber made a bad heating system that killed his grandfather, the outcome is often not good for the plumber. Even so, we have no plans to operate outside our legal jurisdiction.

Thanks everyone for the lively debate on open hydronic systems. I am convinced that if there is any risk to my family, I should avoid it. I'm planning on buying a heat exchanger, but I have doubts about my design from there and I still don't understand my flow problem. I'm going to repost with more specific questions to try to narrow down my flow problem and design a heat exchanger system.