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New installation with high heating bills - HELP

I just returned from guy's house about 90 miles from me who complained about a (new house) radiant system the local plumber installed. It uses s Seisco SH-28 tankless electric water heater on a 1700 sq ft house on a slab. The guy used concrete blankets for underslab insulation but no slab edge insulation. He has been complaining about high heating bills (it is an all electric house). There is no storage tank in the system and my thinking is the water heater is producing too low flow gpm to adequately supply his house (I guestimate needing close to 5gpm total). Would adding a storage tank help reduce his bills, adding slab edge insulation make much of a difference, or is there anything else that would help him?


  • jp_2
    jp_2 Member Posts: 1,935
    more questions than answers

    1.) what was the expected heating costs?

    2.)climate zone?

    3.)ground type, if dry sand and gravel maybe not a real problem? damp ground, a real problem.

    4.)is the house warm? even floor temps?

    5.) what is the supply & return temps?

    6.)what type of heating controls?
  • Contractor
    Contractor Member Posts: 41
    Its the edge.

    No doubt about it. I had to go trouble shoot a guys house one time in the dead of winter with snow on the ground. He was cranking 150 degree water through his 1500 sq ft slab and he was only getting about a 58* room temp. Well i couldve told him his problem when i pulled in the driveway. There was about a 5 foot area around the house where there was not one flake of snow. The sides of a slab is where a majority of the heat loss will be which is why alot of manufactueres only recommend a r-5 just around the edges below the slab but double or more on the side. He has to insulate that side to bring his costs down.
  • Arthur Binder
    Arthur Binder Member Posts: 18

    The homeowner was expecting in the $250 to $300 range.

    The climate is central Illinois.

    The slab was built up with CA-6 and there is no water table present.

    The homeowner said the house feels comfortable but it took a couple of days to warm up when he first started it. He had the system shut down when I visited this am. He is using space heating to keep the house semi comfortable to save on his heating bill.

    The water heater t-stat is set at 115 F. There isn't a thermometer on the supply or return to verify this. Other than that there is just a thermostat and a pump relay. The water heater is designed to come on when it senses fluid flow. It is piped in a single loop.

    The only
  • where the installer?

    Where the installer before you took this 90 miles away job? Sounds like another Radiantbeantec 's job... No side insulations? Inferoir under slab insualtion? Get bigger boiler to overcome the heat lost and send bill to the installer...
  • jp_2
    jp_2 Member Posts: 1,935

    please define "single loop"? please don't tell us the 1,700 sq foot house is on one loop? should be on several loops connected to the water heater.

    couple of days to heat up may not be usual.

    sounds like the only solution might be to abandan the floor radiant and have panel or baseboard installed professionally.

    what did the heatloss calcs say?

    he could dig the perimeter down to the frost line and install 2-3"foamboard, that would help, but sounds like a whole lot of problems here.

  • If it was the first month, you can't judge based on that. Powering up a slab for the first time can take a whole lotta energy.

    That said, edge insulation is always warranted and always a good idea.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928


    Sounds like this plumber should stick to domestic plumbing--either that or do some SERIOUS study...

    Edge insulation is mandatory for an on-grade slab!

    A single loop serving 1,700 sq.ft. is so off the charts that it's beyond impractical--it's impossible. With 3/4" tube at 24" spacing that's 850' minimum with an insane pressure drop even at 2 gpm!

    If the system is as you describe with a single loop, no edge insulation and "iffy" underslab insulation, there really is no hope. Abandon.

  • whoa, my mind blanked out the single loop bit.

    Time for a jackhammer if they have a 1700 foot loop installed.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Worse and worse...

    That Seisco SH-28 has 28,000 watts/hour or 95,000 btu/hour. That "SH" means "space heating". Specifically saw it mentioned that it's warranted ONLY for space heating. Sure hope this isn't a combined space and domestic hot water heating system...

    The Seisco SH series also seems prominent in DIY "it's so simple and we make it cheap" radiant system websites.

    Assuming this space heating appliance is being used only for space heating, I find it hard to imagine that any reasonable 1,700 sq.ft. house in central IL would require anywhere near 95,000 btu/hr or 56 btu/hr per square foot. Are the walls nearly solid single glazed glass with metal frames without thermal breaks?

    20 btu/hr (34,000 btu/hr total) is MUCH more reasonable for a "typical" newer single-floor home of that size in that area unless it's 12' wide and 142' long...

    I have a sneaking suspicion that the HOMEOWNER is the main culprit here--acting as his own contractor and finding people to install what he gave. If true he has NOBODY save himself to blame!!!!!
  • mtfallsmikey
    mtfallsmikey Member Posts: 765
    Another stupid question..different thread

    How much insulation should be around the edge of the slab? My buddy's garage which is heated by radiant would benefit from this...
  • Tony_23
    Tony_23 Member Posts: 1,033
    Wait a minute...

    Nowhere does the original poster state that the system is one 1700' loop or doesn't heat the space. He says the cost of operation is higher than what the HO expected and/or is comfortable with.

    I don't know about Illinois, but if he could heat 1700 sq ft for $2-300 of electric in a winter month here in WNY, he'd be golden. The HO might just've been sold on inexpensive operation as well as installation and isn't realistic in his expectations.
  • steve b_24
    steve b_24 Member Posts: 1
    Details make the difference

    I don't see where the original poster says exactly how much the energy bill is. He states only that "the homeowner was expecting in the $250 to $300 range" and "he has been complaining about high heating bills". How much is he paying? Could it be $500/month, $1000/month? or more?That information is missing. What is realistic? What is the cost of electicity there?

    Aside from the lack of slab edge insulation, what other insulation details might be sub-par? What is the calculated heat loss and cost to heat with and without slab edge insulation? Seems to me that more facts are needed.
  • Arthur Binder
    Arthur Binder Member Posts: 18

    He has six loops of 250' each according to the homeowner (supposedly equal loops). By a single loop I mean the tstat kicks on the circ pump in a single loop from the electric water heater to the manifold and return back to the water heater. The water heater senses flow and kicks on every time the system calls for heat (4-7000watt elements). That's why I'm thinking of adding a storage tank to run a primary/secondary loop, to get the 5gpm needed for the manifolds and to keep the water heater from kicking on all the time. The water heater wants to supply 115 F. I could feed the tank and control that pump with an aquastat then install a pump in the secondary loop controlled by the tstat to feed the manifold. Set the aquastat at 90 F or thereabouts so the water heater won't constantly kick on.
  • Arthur Binder
    Arthur Binder Member Posts: 18

    He paid 475$ last month. The cost is .07585 for the first 800KwH and .05844 additional KwH respectively. Aslo is .02453 delivery charge per KwH. He used 4740 KW from 1/10/07 to 2/8/07.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    At least R-10

    Or the equivalent of 2" EPS (blue or pink extruded polystyrene). The trouble is in detailing what protects it especially as it rises above grade.

    This past weekend I looked at a Campanelli house in Chelmsford, MA. that a friend is looking at buying. 1960 vintage with a York central boiler in the kitchen, original copper piping in concrete. Automatic snow melt around the foundation and even a cricket sitting an moving (very slowly) on the foundation sill in 18 degree weather...

    That is what no edge insulation will do for you.
  • Arthur Binder
    Arthur Binder Member Posts: 18

    The water heater is used only for space heating, although there isn't a double check valve to protect the domestic water. I mentioned that to him while I was there. I did a basic heat calc before visiting the house figuring a 1700' square with 2 windows per side and 2 doors and came up with about 25000btu needed with 5gpm, 8.3ft head. I mentioned to him the water heater had too many btus for the system but not enough gpm flow. Supposedly he complained last month to his plumber and they replaced the original water heater the SH-14 (47780 BTU)thinking they undersized the original heater. I asked him if he still had the original heater that it was plenty and could save him on heating costs if we could get the flow but the plumber damaged it when they changed it out.
  • Arthur Binder
    Arthur Binder Member Posts: 18

    Can you give me an estimated BTU difference between slab edge and no slab edge insulation? My program won't even let me unselect it (I wonder why). I mentioned to him he should dig the perimeter of his house and install at the very least 1" but I would recommend 2" to 3". I would like to give him an estimate on savings by doing this.
  • Arthur Binder
    Arthur Binder Member Posts: 18

    The installer was a local guy. He won't come back. The homeowner got on a website healthyheating.com and emailed Rob Bean who sent him to me. He is out of my area but I told him I would help him by giving him recommendations and a piping diagram so he could have someone closer change it for him.
  • Arthur Binder
    Arthur Binder Member Posts: 18

    I also forgot to mention he does not have gas service to the house. The tubing is Vanguard Vanex potable tubing. I use only Wirsbo tubing so I am unfamiliar with this brand but I don't see anything on it that says it is oxygen barrier. That kind of limits what could be used as a heat source.
  • Heater sequencing

    From what Mike said, the electric boiler is way oversized for the application. Is there any way to control the four heating elements individually? If this was possible you could modulate the heat output to match heat loss and weather conditions. Kind of like multiple firing rates for a combustion boiler.

    I dont quite understand what the storage tank would gain you with an electric boiler. Cycling an electrically heated boiler does not produce the same loss of efficiency that would result from short cycling a combustion heat source. Cycling, otherwise known duty cycle modulation is an effective and routinely used method of controlling output of an electrically powered heater, allowing control without any loss of efficiency.

  • Contractor
    Contractor Member Posts: 41
    O2 barrier

    Vanguard does have a oxygen barrier tubing, but from the sounds of the installer who knows what he used. That wont make any difference in the heating though, it just will with any ferrous compnent that may be in the system (cast iron boiler). again i really believe its the side insualtion, not the length of the runs the controls the hot water source nothin. nrt said the costs would be higher the first month, that is absolutely right, a slab of that size will suck the heat right out of the tubing and at times may need 10-30*F higher water temperature running through it for a couple of days before you can bring it back down to the temp. you were expecting to use. as for the exact btu loss through the side but if you look at my post above (melted snow around the house) and someone elses post about the moving cricket in the dead of winter, you can see that its enough to turn winter into spring around the perimeter.......i cant wait for spring.
  • System efficiency

    The more I think about it, the more I feel that increasing the insulation is the only real answer to reducing the cost of operation.

    Nothing you do on the heating side will make any appreciable difference on the cost of operation, because heating wise it is already 100% efficient. No matter how you pipe it, pump it or control it, all of the heat energy you are paying for is going into the building envelope.

    We are all used to thinking in combustion terms where you have losses of efficiency in terms of flue losses up the chimney or out the vent, and cold outside air coming in for combustion. None of this applies to electric heat. It is 100% efficient by definition, because all of the heat energy you pay for remains in the building until it escapes through the walls, windows, ceilings and floors.

    Whether you have a 10KW boiler or a 100KW one, it will run as long as necessary to meet the heat loss and then shut off, putting as many BTUs as needed into the building. None of the BTUs are lost on the conversion of the electrical power into heat. There is no such thing as an oversize electrical boiler. It will only run as long as required to meet the demand, converting all of the power used into heat. The only real factor is the heat loss. By what method you move these BTUs around is not relevant as long as you meet the heat loss and satisfy the thermostat.

    I dont know if I am saying it well, but I hope explanation makes some sense?
  • Plumdog_2
    Plumdog_2 Member Posts: 873
    A failure to communicate

    If you do the math on the energy usage; your consumer has used up about 1,394,118 btu for the month. (4740 kw x 1000 divided by the conversion factor of 3.4 for elec. resistance to btu). This works out to about 140 therms if he were being billed for natural gas; and at 1.40 per therm, his energy bill would have been $196.00 for the month. Around here, electric resistance heat is more than double the cost of gas. And I suspect the case is the same in Illinois. Also understand that all cooking, clothesdrying, Domestic hot water and lighting is part of that total energy bill. So I don't think the bill is that far out of line. Somebody lead him to believe that Electric is Clean and Efficient but neglected to tell him that it is also very expensive. I would switch to a Propane boiler at the earliest convenience.
  • cattledog
    cattledog Member Posts: 60
    slab edge heat loss

    For slab on grade floor perimeter insulation, tables in the Heating Equipment Sizing Form (Department of Planning and Development Seattle Energy Code) show .73 btuh per degree delta t per linear foot of perimiter, and R=10 insulation around the edge is shown to lower that to .54.

    As an example, the Seattle design day has a delta T of 46 degrees and for an uninsulated slab they use a heat loss factor of 33.6 btuh per linear foot

  • that's interesting. An R2 should cut it in half. I wonder what the calc is they base that on, or what's included in that calc.
  • jp_2
    jp_2 Member Posts: 1,935
    never mind

  • jp_2
    jp_2 Member Posts: 1,935
    gpm ?

    what is the present gpm?

    sounds like the reason the water heater is 'kicking on' is because the house/ground requires it.

    if the water temp was over shooting I suggest a storage tank, but sounds like it doesn't see the 115F the tstat is set at?

    need to look at supply and return temps.

    using electric water heaters makes trouble shooting a little easier. if the electric bill is high, either the house is too warm or the homeowner is causing 'global warming'.

    how many zones? once again though, still need to measure suppply and return temps.
  • hr
    hr Member Posts: 6,106
    The Seisco is a modulator

    as I recall, so it only draws the current needed to meet the load. I doubt the heater itself is the issue.

    hot rod

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  • Steve Ebels_3
    Steve Ebels_3 Member Posts: 1,291
    No use in mincing words

    He's screwed.

    No edge insulation and concrete blanket for under the slab?!! Where does he think is heat is going to go?

    Heat travels more quickly to a higher delta T my good man. If the ground is 30* and the inside of the house is 68*, which presents the greater heat flow path for the 115* degree water.

    A cement blanket is only marginally better than bubble foil but being that it's under the slab which is under the house, there's not a lot that can be done about that problem. Stuffing 3" of foam to a depth of 3-4' around the perimeter of the house will help out a bunch.

    I don't think he has a system problem as much as an insulation (or lack of) problem.
This discussion has been closed.