I live near Lansing, Michigan.  It is about 16 degrees with 14 inches of snow outside, and I have 1800 feet of bright orange Kitec pex pipe running
under my hardwood floor as a staple-up installation.  In Michigan, we are required to use a dual-wall heat exchanger, so I take hot water from my
gas fired hot water heater and run it through a short (8' long) copper pipe to the 1004DW00E heat exchanger and back to the drain valve at the bottom.
The flow rate is 10 gpm in that short loop.  My heating load is 45,000 Btu/Hr according to some Manual J estimate.  My house is a Ranch with 2700 square feet.
The water temperature leaving the hot water tank and entering the one side of my 10-plate heat exchanger, is 133 degrees F.  The water temperature
leaving that side of the heat exchanger and going back into the natural gas fired hot water tank is 119 degrees F.  On the other side of the
dual-wall heat exchanger the temperature out to the Radiant Floor is 119 degrees, and the temperature returning from the radiation floor (6 loops, 300 feet long tied to a distribution manifold) is 107 degrees F.    The flow rate through the 1/2" pex pipes is 4.5 gpm.

What do the experts think?  Should I make some changes to my setup for better efficiency?  Any response will be greatly appreciated.

If you really have a 20 BTU/sq ft heat load, unless you're using plates in the joists you should need at least a 155 average water temp in the loops under design conditions. If you're using plates it should be more like 120 average if they are the heavy gauge variety, so you're close there. light gauge would be in between the two.

you definitely should use an outdoor reset variable speed injection control. cheap, great comfort enhancement.

though I will also note, with a heat load like that, you'd have been better off with a mod/con boiler.

I did put up continuously heavy aluminum transfer plates between the pex and the subfloor. Under that is a bubble-wrap aluminum Astrofoil layer, with R19 batt insulation filling in the joist cavities. I am thinking of switching out my gas fired hot water heater for some sort of Geothermal heating plant. Thanks!

I think that you have a calculation problem. On the heater side, you have 10 gpm X 14 dT x 500 = 70,000 BTU / hr. On the floor side, you have 4.5 gpm x 12 dT x 500 = 27,000 BTU / hr. Which one do you think is correct?

Jeff

I didn't do any calculations. I am just a simple home owner. I am reporting exactly what I am measuring. My neighbor told me that my plate collector is probably
plugged full of calcium deposits. My wife thinks the house is a little chilly, so I thought that I can turn up the hot water dial to a higher temperature. Thanks.

Where are you getting the 10gpm and the 4.5gpm numbers from?

you're 5-10 degrees under the average temp you should need for the WHOLE HOUSE AVERAGE at design day.... you may have individual rooms with higher per square foot demands as well, which would be even further behind.

If you were to turn your water heater up 10 degrees, from 133 to 143, you'll increase the heat output on the other side of the heat exchanger (going to the floors) by about 20%. The hot water temperature on the floor side of the HX should go up by about 7 or 8 degrees; the cold side coming in from the floors should go up by about 5 or 6 degrees. This increase dT on the floor side will represent the extra amount of heat that's going into the floor.

So, you should see an increase from 119/107 (dT=12) to about 127/113 (dT=14).

Your efficiency losses out of the water heater will also go up, as the water heater will shed more heat into the room where it is located, and the combustion off producing 143 degree water is marginally less efficient.

Jeff

I have Blue-White flowmeters plumbed into the copper pipe runs. That is where I am getting the gpm flow rates from.

When I bought this house, it had a 2 ton A/C unit installed. Could it be that my Manual J estimate is not accurate?

A guy at church told me to try to slow down the water flow through the floor with a half-open shutoff valve. He said
that way more heat would transfer to the house from the floor. I so greatly appreciate any guidance on this as so
few local HVAC people know anything about Radiant Floor heat. They all recommend tearing it out and putting in a
new furnace.

My hot water heater was purchased in 1992. It has an E-value of .52. To me, it seems that most of the heat is just going up the flue and out the top of the house.

heating efficiency on a unit like that is probably about 70%.

Slowing down water flow never increases heat transfer. It may increase temperature differentials, but you will always transfer less energy with less flow.

Either your temperature, or your flow on the water heater side of the equation have to be wrong: it would say you're dumping something like twice the output that water heater is probably even capable of and far more than the radiant system can even put out.

Regardless, you probably need more temperature on the radiant side, can't say how much without a room by room load calc, and a change in heat source would make sense. At these water temps, Geo is out, and I would recommend cutting out the water heater, heat exchanger and putting in a modulating/condensing boiler. AFTER you know what water temps you really need.

One of your flow meters is simply not working correctly, almost surely the one on the hot water side of the heat exchanger. It seems unlikely that you are putting 70K BTUs / hour into your house.

In response to the church guy, you can never, ever increase the output of a heat exchanger by slowing down one of the flows; you can alter the supply and return temperatures, resulting in a higher temperature differential, but that effect will always be overshadowed by the decreae in the flow rate that caused the temperatures to change. Don't do that.

I believe that there are only two ways that you are going to get more heat out of the system as it is: You can either turn the water heater up, or increase the efficiency of the heat exchanger by either increasing the flow on the water heater side (larger pump, or cleaning it out) or installing a larger, more efficient heat exchanger. However, while I do think that you should clean the HX if it's crusted over, I do not think that there is much hope in installing a new pump or buying a larger HX - those options just won't be enough to make as much of a difference.

Jeff

All of your questions are normally answered in the first stage of any radiant floor heating system installation, that being the design stage.

Water heaters are not boilers.

It is unlikely that your water heater can be set high enough to overcome the temperature drop through the heat exchanger and still satisfy the load. Room temps falling behind, ticking noise on start-up, high fuel bills and a new water heater in about 5 years.

Double-wall heat exchangers waste energy and discount performance by definition.

There are online vendors that do "free" design that might have gotten you closer, but the first step in any DIY project should be to secure a professional design. The time and money wasted is sometimes beyond imagination. Usually it is just the extra pumps, heat exchangers and unnecessary "trim" but in your case I predict the fuel bill will be high and the comfort low.


DIY design, always the first mistake.

Sorry, I get excited.

None of us can really help with the information you can provide.

Maybe these links will help.

http://www.badgerboilerservice.com/contractor.html

http://www.radiantpanelassociation.org/custom/directory/index.cfm

Badger,
I am so happy that you get so excited. It must be that you have so much passion! I did pay $1500 to a HVAC design professional. The main mistake was that I read the
flow meter on the Hot Water side in Liters per minute not Gallons per minute. So that flow rate is 10 liters per minute on the hot water tank side, if that makes a difference.
My Bradford White water heater was purchased in 1992. Your professional words "a new water heater in about 5 years." probably need a reference date, since I have already
run my system for 5 years. I expect my water heater will still be going strong after you have retired. In general the system heats the house well. My heating bills are lower
than anyone else in the neighborhood. I suspect the engineer who did the Manual J was another HVAC professional. In my opinion the heating load on this house is closer
to two tons than his number. I think HVAC professionals do that to sell more expensive furnaces. I can't very well change the stupid law in Michigan, which is only one of
three states which require a double-walled heat exchanger. I think this is because the state has a very strong HVAC/Plumber union going, along with the auto worker unions.

Maybe if someone wants to help, they would tell me what measurements to supply? I would be more than happy to hire you, Mr. Badger, but it does sound like you are
very biased towards boilers; when maybe a few Solar panels or a Geo unit could be used in place of the hot water heater and heat exchanger?

Another quote from your website "Hot water heat and more specifically a properly designed and installed RADIANT FLOOR HEATING, is silent and comfortable, without air movement."
We love the quiet system which extremely is comfortable!! However, we don't understand how the particulate matter gets removed from the air, since you are not moving 1500
cfm of air through that expensive electrostatic Aprilaire duct filter we have sitting by our unused 96% efficient Bryant Evolution System Plus gas furnace which we never use. So when
my wife burns dinner and my neighbors come over and smoke in my house, and the dog hair every where, what is my radiant floor doing for my air quality, Mr. Badger?

Two tons was a cooling load, I believe. that has very little to do with your heating load calculations, most of the time.

If the heat load were half what the Manual J were calculated at, then the water temps you are delivering would likely be quite adequate. I believe you have indicated that is not the case, and the facts seem to show that your Manual J may be in the right ballpark. Which means you'd be better off with a mod/con boiler (which didn't exist in 1992) in all liklihood, and the temps are too high for geothermal to be a good choice. to do Geo you really want a maximum water temp of 115 or lower, and the cost of a geo system would be far greater than this heat load is likely to justify even if you did get the water temps down to optimal geothermal levels.

Solar for heating is really a joke in any typical home. you'd never get enough panels to put much of a dent in the load. for DHW it can make good sense.

While I disagree with Badger regarding the ultimate great nature of mod/cons as superior to any other choice, in your case, with the info you have provided, it would be the right choice. You could probably reduce your fuel bills by 30% or more here (roughly 70% for EF 0.52 water heater to 92%-95% for mod/con boiler). though, honestly, if that gas furnace was installed properly, you could probably save money turning off your water heater and using that too. Of course you'd take a comfort hit in that case.

Your fuel bills being lower than anyone elses on the block doesn't mean that much: if all you did was avoid having a cast iron boiler 3x as large as your load needed hooked up to a high temp system (or furnace, for that matter), you'd probably be significantly below your neighbors with no other changes, and you successfully did that. The average efficiency of this relatively poor quality heater is still significantly better than a vastly oversized cast iron boiler or furnace.

Radiant is air quality neutral. Furnaces are not, though any modern house needs at least an indoor quality air system such as ERV with basic filtration.

Rob, thanks for all the wonderful guidance and advice! It is very interesting that the company from which I purchased this radiant floor went out of business during the recent recession. So, right away, I get jumped on as one of those stupid DIYers. The system cost me $10,000. I think much of it was labor. As I said, I made the
mistake of reading the one flow meter in LITRES not GALLONS per minute. In general the system has worked well for us, until we get in the minus temperatures with gusting winds. The Geo sales guy said he would want to run the floor temperature much lower, around 90 degrees. He said the Geo would run longer, and would take longer to heat the house, but would be way more efficient that a Badger Boiler. Now you can see why simple homeowners get so frustrated. If they make the mistake of talking to more than one HVAC guy, they get wildly different Manual J estimates and totally different proposed solutions. Experts like Rob and jbaron are hard to find.

Badger too. He may be a bit crustier than I, though. being older than dirt does that to a guy oh, i kid, I kid!

your measurements still don't quite match. seeing something like 27kBTU output on the load side and only 18kBTU on the water heat side. but regardless: it's the room by room totals that matter if you want to figure out what it will take to keep up consistently.

or get some two stage thermostats and wire in that furnace for backup.

I would get quotes on a mod/con, though, if I were you

I am not an expert, just a homeowner with a solar enhanced radiant heating system. Just ask Rob.

BTW, one thing that Rob left out in his last note - regardless of what the geo guys SAYS, you will NOT be able to heat your house with 90 degree water in the floors. That's what you are seeing right now - a need for 120 degree water. Saying that 90 degree water will work but that it'll "take longer" is simply incorrect. I'd stay away from that guy, period.

Regarding your measurements (again): my guess is that you are reading gauges. I don't know how accurate flow gauges are, but those temperature gauges that fit into wells in the line are notoriously inaccurate. You can tune them a bit, if you can and if you have not already, using boiling water. My experience is that they don't stay tuned for very long, but for immediate use, this works.

Jeff