Radiant Heat - Water Heater?

Ralph_2

I have 8 loops at about 200 or 250 feet each running through concrete floors. I was going to hook all eight runs to one supply manifold and one return manifold, and place the pump before the supply manifold. I don't care about zones right now, but it is configured so zoning could be achieved later on if desired. I figured that with 2000 feet in eight loops I needed to have 120 feet of head, which is easily achieved with a jet pump or multistage pump. Did I calculate incorrectly?

Ralph_2

Water Heater vs. Boiler - Radiant Heating

I am installing a Wirsbo radiant floor heating system in a concrete floor. Is there a problem using an electric hot water heater as opposed to a boiler for a heat source? I suppose it has a lot to do with hot water recovery time? Square footage being heated? Any input would be appreciated. Also thoughts on sizing and type of circulation pump.

Thanks for any help!
Ralph

Dale

input

The only problem is low input and high cost of electricity compared to other fuels. if you want to use an off the shelf electric heater you better have a fairly small load like less than 18,800 btu figuring a 5500 watt heater and 3.415 btu/watt. Hot Rod who posts here uses little electric heaters for small bath radiant. Nothing magic, do the heat loss and see what you need. As for a pump keep the loops less than 250 feet and figure 6 feet of head needed per hundred feet.

Radiant Wizard

Water Heater

It all depends on the application. I personally don't like to use them. The problem that I continually run into is floor response time. A real good control strategy is a must when utilizing a water heater. I've seen many unhappy radiant customers when water heaters are used. If a boiler is available then use it.

hr

For small loads

say perhaps below 20,000 BTU/hr. And supply temperatures below 140 degrees, there are certainly some applications for water heaters, I feel. I have been using whs for 10 years or more, seems the only failures are the CombiCor tanks, designed for dual use with intergral double wall HXs!

Keep in mind local code requirements. Also, most if not all water heater manufactures warranties are void if water heaters are used as stand alone heat source for hydronic applications, if that is important.

I see no reason why 10 year life expectancy shouldn't be expected with a low pressure closed loop application, like this. I've seen 30 year old water heater radiant jobs in my town. Yes more than one!

Electric would be my last choice in most areas, unless you are in the 5 cents or less per kilowatt hour area

Small floor warming requirements are a good match for water heaters, with all the above in mind.

Control is simple, a thermostat turns on the circ pump! On most of my electric tank, small, 1 zone jobs, I run constant circulation and use a small contactor to call on the water heater. This minimizes standby loss and allows the tank to shut down in warm seasons. Constant circ is nice also, to minimize temperature swings, and take advantage of solar gains.

hot rod

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Ralph_2

Tankless water heater?

How about using a tankless electric water heater?

I would like to use electric because my electric rates are under 4 cents per kwh.

frank s

That would be a big NO

Just from my research, and conversations with others....not a good idea... RADWIZ what do you think? I hope you're feeeling better......ick!

hr

Tankless electric

contact John Wood at Azure Supply, he has a bunch of Seisco modulating electric tankless installed on radiant. I tried one but ran into problems with the high limit kicking when the pump quit. Perhaps I was running it too close to temperature limit. Ideally they would modulate output based on load. Sort of an automatic outdoor reset.

I believe Watts is also labeling that Seisco unit. Probably see it on Watts Radiant panels soon.

Plenty of electric boilers available also. Cast iron and steel. They generally go down to 4500 Watts, and I'll bet you could downsize the element even more.

Electric make some sense at that price! I can see your logic.

hot rod

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Ralph_2

Specific tankless choice?

I think I'm going with the PowerStar AE125 electric tankless water heater. Provides 3.7 gal. per minute for water usage at 105 deg. F (assumes 55 F inlet temp.) It sells for $598, shipping included. See the link below. Does anyone have an opinion?

Thanks!

Ralph

http://www.homedepot.com/prel80/HDUS/EN_US/diy_main/pg_diy.jsp?CNTTYPE=PROD_META&CNTKEY=misc/searchResults.jsp&BV_SessionID=@@@@0894121201.1070466758@@@@&BV_EngineID=ccecadckdhilgejcgelceffdfgidgml.0&MID=9876

Radiant Wizard

Frank!! Tell them

about the nightmare you ran into concerning a water heater. HR thinks that control is just a therm. I would agree only if I was doing floor warming not actually heating a space.

J Van Lund

Electric Water Heater

The tankless folks at ECC weren't encouraging. So we used a 40 gallon Bradford White Electric Water Heater dedicated for a 1.5" thick concrete slab (mix was heavy on stone and difficult to place). Some folks in the know are using self-compacting concrete. Rewired heater for 11,000 watts (two 5500 watt elements) of simultaneous heating (voids warranty) Specifics: 1500 sf, 10 loops with 9 less than 200 feet and one at 250 ft, 5 thermostatically controlled zones, 24,000-25,000 BTUh max heating load in the Puget Sound area of Washington State. Used Wirsbo thermostats, Rehau Pro-Balance manifolds, and a Grundfos UP15-42SF circulator. Max supply water temp 110-115F. Measured max flow for all loops running 5 gpm, 6 ft. of head, Delta T=15 deg F. For five loops running, 3.75-4 gpm, 7 ft. of head, Delta T=12-20 deg F. Very satisfied with heating comfort. When we are away and lower the thermostats to 55F, it takes about 6 hrs. to raise temperature in house 10F, but once it is raised it stays there and won't run again for 6-8 hrs. Max. winter usage is 55-60 kwh per day for all electrical demand. Be sure to place circulator downstream from expansion tank/air separator to eliminate air noise. We need to re-configure our system to do this. I am very appreciative of all the great people who have helped me learn something new!!! Hope this helps.

Ralph_2

Where can I find a good diagram?

I am pretty sure I'm going with a tankless water heater capable of keeping water at 105 deg F at 3.7 gpm, and a pump that with 133 ft of head at 3.5 gpm flow rate.

This is my first install, so any help in the control room would be appreciated. What types of thermostats are there, and how do they get connected to the pump and heater? The heater should work whenever load is applied, and I figure the thermostat should just turn the pump on and off. What about the expansion tank and circulator? Also, I am planning on running off of one manifold with no zone control. Is this OK?

Thanks again!

Mark Eatherton1

I hope...

thats a typo, because if you find a pump that will generate 133 feet of head @ 3.5 GPM, you'll be able to heat the house with the motors standby losses...

Maybe you missed a dot or something???

ME

ALH

Give it time

Electricity rates are only going up. Avoid electric appliances if at all possible. From a conservation standpoint electricity is valuable energy. I would prefer to use electricity for only those applications where no other energy source will work. ie this computer i'm using to access The Wall

Kal Row

133ft

you never know -
i have seen people have buried hundreds of feet of pex in concreet before realizing that they need multiple loops

J Van Lund

Diagram Information/Professional Help

See Radiant Panel Association's (RPA) website http://www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=1 or Bill Clinton's article in November JLC 1998 "Using Water Heaters for Radiant Heat." You can get Bill's article off the web. Using Google, type in JLCOnLine and find it. These diagrams are just schematics so you should consult an expert. You can find experts in your area from the RPA member list. Strongly recommend getting professional help because so much can go wrong with hot water under pressure. These guys have learned so much based on experience. Experience is a hard teacher. She gives the test first and the lessons afterwards.

Kal Row

hot water heater

if you use primary/secondary with vari speed injection (you can buy them ready made) - any heat source will do -if you are going to a snow-melt loop - you need a flat plate heat exchanger or the oxygen will annihilate your heat source, unless you really trust oxygen barrier pex, (dont forget an expansion tank both sides of the heat exchanger)

you can use a good old fashioned gas or electric domestic hot water heater - however if you are also using it for domestic hot water also , you again need to use a flat plate heat exchanger - and of course the cold water supply
will also need an expansion tank, a backflow preventer, and a thermostatic mixing valve, as the heater it will probably
be set for 140+ to give you the decent dual use capacity
(also on thermostatic mixing valve - if you are using a return loop and pump for your domestic hot water - then the hot water return AND the cold supply, have to, BOTH, and ALSO go to the cold inlet side of the thermostatic mixing valve with checkvalves on each - this way return water tempers the loop when no hot water is drawn)

my local plumbing supply in Brooklyn NY is using a hot-water heater to power it's radiant system, going into this huge and thick 8000 cubic feet of slab, it takes an hour to heat up - but stays hot overnight - since they are using it just for heat, a thermostatic bypass valve works for them

if you do use a hot water heater, please mount it so that you have 3+ ft of clearance above the anode rod so that you can change it every 5 years, and replace the tank drain with a full port ball valve going to a washing machine style drain connection so that you can blast flush the sediment every 6 month - AO SMITH has a 30+ yr old one in their shop treated exactly that way, and of course dielectric unions for the water cinnections (watts 3001A 0821420 or equivalent) you don't need your system to be corrosion battery, people expect a heating system to last 30yrs

Dave_16

NO,NO,NO

Slab sensor no t-stat, must have plates, not good for joist heating, in my opinion not even for floor warming ,though it does depend on installation

Ralph_2

Professionals?

I have not been able to find professionals in my area, but some HVAC guys are really interested in learning about it. I live in Lexington, KY, and apparently some hydronics have been installed for snow melting, but not for whole house heating...

Mark Eatherton1

Too much head....

The head pressure is based on the highest pressure drop circuit, not the cumulative total of all the pressure drops.


A Taco 007 or a Grundfos 1542 or 1558 will work just fine for you.

ME

Kal Row

design..

i hate to plug someone else's stuff, neverthless, here goes..

go to John Siegenthaler's website
http://www.hydronicpros.com
and order the combo, it's money well spent,
and will bring you up to speed real fast,

also, watch Dan Holohan's
"Classic Hydronics!" (dvd or vhs)
it will give you a quick smaterring of the whole subject and the why's of it, in a most enjoyable fasion. even people not intersted in hydronics like to watch him, i have lent his dvd's to many friends

Kal Row

fyi

> The head pressure is based on the highest

> pressure drop circuit, not the cumulative total

> of all the pressure drops.

>

> A Taco 007 or a

> Grundfos 1542 or 1558 will work just fine for

> you.

>

> ME

Kal Row

in case anyone cares

a taco 007-fci (internal flow check) has a better pump curve than a 007 with a seperate external flow check, but the grundfos 15-42FC (flow check) does not,

if you go to the gundfos, you need the 15-58FC which is currently avail only in a UPS model (the S stands for multi-speed) and will cost you 40 dollars more based on the plumber's price of 57 for the taco and 106 for the grundfoss - the grundfos is better for 4 reasons:

1)the flow-check is on the discharge side which inherently give a better NPSH (Net Positive Suction Head) - you dont want any restriction near where the pump is dropping the pressure since if your vapor pressure is near the edge, a slight restriction may throw it into cavitation, so, if the pump sounds like it's pumping gravel - it's cavitating - and will self-destruct in a short time - do something about it, increase the system pressure, drop the themprature, etc

2)the flow check on the grundfos is easy to get to

3)you might discover that you dont need the high speed of the pump and save electricity by dropping the speed instead of shutting the balancing valves more

4)wet rotor pumps tend to stick if not used for 30days or more, you can twist to free the rotor on the grundfos via an external cap - and is generally better quality - Danish company - built in germany - good old tutonic percision

ps - the sticking may not be a problem for you since a lot of the newer boilers exercise the pump a minute ever 30days,
check with you boiler manufacturer, also if your pump is controled by a tekmar controler, most of them do it too