Radiant is definitely a set it before you need it and leave it there type of heat. If you need quick recovery, you should supplement with another type of heat. The 'recovery' seems to be the key...length of loops, number of loops, number of zones, undesired heat loss out of the slab, size of tank all play a part in that. I had the same thought as you regarding the standby loss of the tank...it's not going out a flue, it's staying right in the area that you're heating. The tankless units are almost a no brainer as long as they're sized to your heat load. The tank units are a bit trickier as the water doesn't heat as quickly and you're paying to keep the water in the tank up to temp even when the system isn't running so you have to be careful not to have such a small tank that it can't keep up and such a large tank that you're heating too much standing water.
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Hot water heaters for radiant heating
- Thread starter MR P BODY
- Start date
My shop is 60x60, 10ft ceilings with 13 loops at 250-300ft/ each. When we built the system last year, we tried to go the cheap route and do electric hot water heaters. We installed two, 80gal Whirpool 9kw (dual 4.5kw elements in each hot water heater), hooked them up in series and tried to get it to work. Never worked at all.
I found this area of the Garage Journal while looking for inputs on LP tankless boilers (possibly the Takagi T-K Jr) as a possible heating source for my setup. I've seen mixed reviews, but after finding out that the two electric hot water heaters cannot keep up with the GPM that we need for the shop, I'm worried about a tankless boiler being able to keep up either...
I found this area of the Garage Journal while looking for inputs on LP tankless boilers (possibly the Takagi T-K Jr) as a possible heating source for my setup. I've seen mixed reviews, but after finding out that the two electric hot water heaters cannot keep up with the GPM that we need for the shop, I'm worried about a tankless boiler being able to keep up either...
autoxbrian
Well-known member
What are your GPM needs? do you have the full system design? I can give you a much shorter amount to look into, because trust me I did an INORDINATE AMOUNT of research on the subject.
Although, if you went with electric water heaters w/o luck (as did I) why are you now looking at gas tankless rather than electric tankless, asuming you already have larger electric lines run just for the system. Thanks.
Although, if you went with electric water heaters w/o luck (as did I) why are you now looking at gas tankless rather than electric tankless, asuming you already have larger electric lines run just for the system. Thanks.
The system is pretty straightforward currently (and not working...lol). 3 zones that are all built identically other than the number of loops. One Zone has 7 loops. One with 4 and one with 3 (oops... 14 loops, not 13).
We have a main input manifold that is fed from our water heaters. This drops into the 3 Zones. Each zone has a Taco pump on the input (will need to get the part number tonight) that is hooked to a thermostat in each of the zones. Out of the Taco Pumps, we run into a distribution manifold that feeds the inputs to each of the PEX lines for that zone. Each loop is approx 300ft long (within 15 ft) 1/2 PEX. Output of each of the loops feeds into another distribution manifold which goes through a 1-way check vale and into a mixing valve that allows us to feed some of the return back into the intake loop. The mixing valves are closed now, feeding all output through another 1-way valve and into a main output manifold that feeds to the bottom of the 1st hot water heater as a return line. Output of that water heater goes to the input of the 2nd hot water heater, then output of that heater goes to an air bleed and then back into the input manifold for the three zones.
We have a main input manifold that is fed from our water heaters. This drops into the 3 Zones. Each zone has a Taco pump on the input (will need to get the part number tonight) that is hooked to a thermostat in each of the zones. Out of the Taco Pumps, we run into a distribution manifold that feeds the inputs to each of the PEX lines for that zone. Each loop is approx 300ft long (within 15 ft) 1/2 PEX. Output of each of the loops feeds into another distribution manifold which goes through a 1-way check vale and into a mixing valve that allows us to feed some of the return back into the intake loop. The mixing valves are closed now, feeding all output through another 1-way valve and into a main output manifold that feeds to the bottom of the 1st hot water heater as a return line. Output of that water heater goes to the input of the 2nd hot water heater, then output of that heater goes to an air bleed and then back into the input manifold for the three zones.
We went gas when we initially built the shop as there is no gas or LP service to the area. We didn't want to bring in a Propane tank and have to have it filled and at the time (last winter) propane was crazy high here (Kansas) and it just seemed easier/cheaper to do all Electric.
After $500+ monthly electric bills last winter, I'm kind of gun-shy of trying anything electric again. The water heaters were running 24/7 and we couldn't get any change in slab temperature furthour out than 2ft from the manifold inputs into the floor.
After $500+ monthly electric bills last winter, I'm kind of gun-shy of trying anything electric again. The water heaters were running 24/7 and we couldn't get any change in slab temperature furthour out than 2ft from the manifold inputs into the floor.
autoxbrian
Well-known member
Same issue I had with 1 80gallon electric whirlpool unit (same 4500W element). And over $550+ bills, when the rest of the house is BRAND NEW, 100% electric with Geothermal... so I was stunned and annoyed as well. Re-evaluated the proposition as our tank was also running 24/7 with barely holding mid 40s temperature in the 1700sq ft+ garage. I went with basically a 20KW tankless electric unit, and electric bills dropped to approx $280-340/month (this is with a 14.9 cent/KWH company!)... I understand the gunshy thought, my experience, I'm more comfortable with a 100% efficiency electric unit.
I would be looking for another form of heat if they were still in the $250+ per month range. My business cannot afford that kind of heating costs, which is what I am anticipating on any Electric-generated heat. I will start another thread for inputs on my setup so I dont hijack this thread any longer.
Dragster Racer
Well-known member
As far as standby losses, where do those losses go? Well, into the room that you are probably heating, right? My research tell me that the two important things are the heater efficiency and the btu input of the burner. Tank size probably has little to do with it in many cases, although a small tank with a small burner wouldn't be up to task. I can see how an electric would be hard pressed to keep up, and would never get the water completely up to temp though.
I may be talking out my **** here, but I thought that even though electric water heaters have 2 elements, they both will not run at the same time unless you rewire them to. So if that is the case 9kw converted online is only 30,000 BTU's. That is not alot of heat for that much space. Did you calculate your heating requirements? I am building in Kansas with radiant and calculated 40,000 BTU's for a 26x48x13 with a well insulated structure and slab at 60F.
*EDIT* Sorry just saw your personal post.
*EDIT* Sorry just saw your personal post.
Last edited:
KenB
Well-known member
Well I ended up getting a Takagi boiler... ramp up type from 4k to 144k... I just finished
the install and will fire it up next week(waiting for a low pressure alarm)
Thanks all
Well, how does it work? I'm thinking of doing the same thing.
Ken
wayne
Member
I have used (am using) one. Works fine, second year, Winnipeg winters, 24x28 shop. Small water heater (7 gals?) removed 1500 watt element, replaced with 5000 watt. In the dead of winter unit comes on for a while then off for as long as seven or eight hours.Any of you use a hot water heater for your radiant heat source, I have been
looking at boilers but they are outrageous on price
Thanks for any help
Circulating pump runs all the time, heater runs only when thermostat calls for it. I keep shop at about 60 degrees all winter. Shut system off for summer-like months. Majority of people I know of are using hot water tanks. 50 - 50 water Glycol mix.
dirttracker18
Well-known member
I know this thread is a little old and it's getting warm but I have a question for those running an electric hot water tank. I am currently using this set up and am wondering about how your system is balanced.
First off I have a 40 g tank rewired to run both elements. I have one pump that turns on only when heat is called for by the thermostate. I have a temp value that is manually adjustable to mix hot water with floor return water.
My question is about the settings for your systems:
What temp is you tank set at?
What temp water to you put into the floor?
I would like to get an idea of where to set this up for optimal performance. I have seen lots of opinions as to why not to use this system but some people seem to be very happy with it. Even if you have a gas fired tank, same questions. Particularily if you have a similiar set up.
I hope to go geothermal perhaps next year (house and shop) but it is just not financially feasable right now.
First off I have a 40 g tank rewired to run both elements. I have one pump that turns on only when heat is called for by the thermostate. I have a temp value that is manually adjustable to mix hot water with floor return water.
My question is about the settings for your systems:
What temp is you tank set at?
What temp water to you put into the floor?
I would like to get an idea of where to set this up for optimal performance. I have seen lots of opinions as to why not to use this system but some people seem to be very happy with it. Even if you have a gas fired tank, same questions. Particularily if you have a similiar set up.
I hope to go geothermal perhaps next year (house and shop) but it is just not financially feasable right now.
Dkramer
Well-known member
After reading most of this thread I am adding my thoughts. With any heating system, for it to work properly, the heat source has to be sized for the heat loss of the area to be heated. If the loss is less than the BTU capacity of and electric water heater, it should work just fine. If the heat loss is greater than the most expensive/efficient boiler, it will not work.
As mentioned a water heater only allows one element on at a time. dirtracker18 has done it right by rewiring to allow both elements to operate at the same time. Just remember to increase power size for the added load.
The most important area in preparing for a radiant system is slab insulation. The slab needs insulated under and around the perimeter.
We have installed just about every type of heat source for radiant applications, electric, tankless, gas/oil fired boilers, and geothermal. All work very well because the heat source was sized accordingly.
Now my personal preference around here is gas fired. The cost of electricity is relatively high here. Plus gas/oil have a faster recovery rate. (We did a job for the state last year using electric boilers. I would love to see there electric bill.)
Another thing to remember about radiant. It is not like a regular heating system in that you should not turn it on and off. I would not change temp more than a few degrees. The plus about radiant is that once the slab mass is warmed up, it stays warm for a while. You can't turn if off for a few days and expect quick heat recovery. Sorry if I repeated anything that was already mentioned.
As mentioned a water heater only allows one element on at a time. dirtracker18 has done it right by rewiring to allow both elements to operate at the same time. Just remember to increase power size for the added load.
The most important area in preparing for a radiant system is slab insulation. The slab needs insulated under and around the perimeter.
We have installed just about every type of heat source for radiant applications, electric, tankless, gas/oil fired boilers, and geothermal. All work very well because the heat source was sized accordingly.
Now my personal preference around here is gas fired. The cost of electricity is relatively high here. Plus gas/oil have a faster recovery rate. (We did a job for the state last year using electric boilers. I would love to see there electric bill.)
Another thing to remember about radiant. It is not like a regular heating system in that you should not turn it on and off. I would not change temp more than a few degrees. The plus about radiant is that once the slab mass is warmed up, it stays warm for a while. You can't turn if off for a few days and expect quick heat recovery. Sorry if I repeated anything that was already mentioned.