Hello, I purchased my home 3 years ago. The house is just over 3500sqft. It has in floor heat up and down in a addition added in 2005-1388 sqft (home built in 1992). The in floor heat setup uses a primary 50 gallon gas water heater 46000 btu and a off peak 80 gallon electric water heater 4500 watt upper and lower element. The in floor heat system is lacking and or the water heaters are showing there age. The system has 2 zones one up and one down. It uses manual adjusted Honeywell thermostats, again one up and one down. The gas water heater runs A LOT, if just the upstairs zone calls for heat it will catch up and shut down in about a 40 min. The downstairs zone will run for over 4 hours and still not catch up (30 degrees outside MN). However, it will make progress. I have temp sensors on the supply and return. 125-130 degree supply and 110-115 return temps on average. This is at approx 30 psi. I have the T stats set at 68. The floors get pretty warm and you know the system is on. My concerns- 1. The T stats are 5 feet off the floor. The ambient air vs floor temps are vastly different as we all know. I would like to upgrade them but am unsure of what T stat to get. 2. My water heaters are either undersized, crapped up (I did flush them- not very dirty), or just to old. I do know the electric water heater is set at 150 degrees. It's where the previous owner had it. I did do a heat loss estimate and IF my calculations are right I am losing approximately 18000 btu per hour in the addition. Any suggestions, thoughts, and wisdom would be very appreciated. I should add that the older part of home is forced air heated/cooled

If the water is coming back at 110 º the fault lies with the emitter not the heaters. For some reason the heat cannot leave the water fast enough. You will need to describe what the infloor heat is. In concrete, under floor, what the pipe size, is how it is distributed, what the floor covering is etc.

Has this been a problem since you bought the house or is it something that has just started?

It's been like this since I have owned it. The gas water heater is marked on the "B" setting. The floor is in concrete in the basement and plywood on the main/top floor. 1/2 inch PEX, carpeted up and down. The insulation used was Johns Manville Comfort Therm R19 interior batts between floors As far as how its distributed (if I am following you correctly) is that the 2 zones are parted 4 ways up and 4 ways down. NW,NE,SE,SW are marked on the PEX. Are you thinking the carpet is the issue?

Correction- 3/4 of the upstairs floor is carpet. The other is tile flooring. It takes quite awhile for the heat to come back at 110-115. The colder it gets the longer it will be of course.

If your water heater is set for 150 and can't get to more than 130, then you need a more powerful water heater. But more insulation or running a duct from the other side of the house may make more sense.

No, actually the 10 to 15 degree temp drop that you are apparently currently generating is exactly what you want for a residential system. However, a well insulated building with high efficiency hydronic radiant floor heating system only requires a supply temp of about 85F (slab temp of about 74F) . So you apparently have a very inefficient underfloor system.

""It takes quite awhile for the heat to come back at 110-115.""
This may indicate some fairly strong heatloss somewhere. First guess would be no insulation under concrete slab but that would not be as effected by colder temp.
My guess is some air leakage into the joist space, probably no plates, thick pad and thicker carpet. If there is infiltration from the trim joist or other areas of the envelope the water in the pex will get quite cold prior to returning to the heater at a heat demand.
Upstairs is one zone split four ways. Tile surface cannot sustain higher temps without being uncomfortable.

Maybe try shutting down the basement and then check the response on the main floor. If the main floor efficiency improves then it may be wet soils under the slab with no insulation but I think the issue is the main floor although heavy floor covering of the basement concrete slab will also decrease the performance.

Just for clarification, it is just the addition that is being heated by the radiant correct?

To get an incremental increase in efficiencies, you might try putting a programable stat on the basement zone and reverse setback that floor.

The stats are fine and what we use on some of our most sophisticated design work.

You need a little engineering, with heat load analysis and review of the installation materials.

Just off hand, a single properly sized high efficiency condensing boiler with outdoor reset, properly programmed, and an indirect-fired water heater for domestic hot water. We design a lot of radiant floor systems using dedicated and integrated or "combi" water heaters, but these are for modest loads e.g. cabins, additions, basements etc.

Don't be distracted by conjecture, pay a qualified professional to run a heat load and design a proper system.

MA - It is assume that when someone has an 80 gallon off peak resistance heater that his off-peak power costs are cheaper then his gas costs.

True, OP doesn't say what control toggles between gas and electric, but it makes little sense to have the gas heat up the basement slab just prior to the off-peak coming on.

Programming to store lower cost heat in the slab as well as the 80 gallon heater should decrease his overall cost assuming that there is a decent cost differential between peak and off peak.

And just maybe he needs a little more than "a little engineering".

And yes OP, put the coffee on, call the Badger since he's in your backyard. One set of experienced eyes can tell you more in a minute then ten days of conversation on this forum (but it won't be nearly as much fun!) If his bill is more then what he can save you in fuel in one year it would be a surprise to us all.

Please define "plate". I am assuming the insulating or not insulated concrete floor.

I appreciate the feedback from everyone. I will try to answer all the questions without jumping all around. The insulation could or could not be the issue. The addition appears to be insulated quite well. R19 batts inside and R 38 in the attic. Quite possibly the carpet is the big part of the problem. The utility room has a bare concrete floor and it gets very warm. Now the heaters are located there and the space is roughly 8x10 there's a lot of radiating energy. I would venture to say at least 14-16 inches of cellulose in the older part of the homes attic. When I say it takes quite awhile to get to 110-115 degrees on return, I should have also stated the system hovers around 80-90 degrees when not flowing. I have tried shutting down the basement and the upper level recovers much faster then the basement.- 30-40 min at 30 degrees outside. Then cycles of 5-10 minutes when warmed up. When both zones run it takes 4 or more hours to recover ( maybe longer runs and more water needed to heat in the basement) I am a believer that the hot water heaters used are not up to task. I think the water heaters are showing there age and or the whole system needs a flush, maybe both.The pumps will run non stop all night and my concern of the T stats. I can rotate the manual knob 3- 4 degrees before pump start up or shut down. The system is being ran on straight household water, maybe better heat transfer with a anti freeze mix?. From reading and understanding things I believe mine is a closed looped system. I have other water heaters for the master tub/shower in the addition. Badger is right- I was going to start throwing money at T stats but I figure its wiser to call a expert. Now who a expert is or is not is the real question.

Just the addition is radiant heated.

Posted By FBBP on 22 Nov 2013 02:46 PM
MA - It is assume that when someone has an 80 gallon off peak resistance heater that his off-peak power costs are cheaper then his gas costs.

True, OP doesn't say what control toggles between gas and electric, but it makes little sense to have the gas heat up the basement slab just prior to the off-peak coming on.

Programming to store lower cost heat in the slab as well as the 80 gallon heater should decrease his overall cost assuming that there is a decent cost differential between peak and off peak.

And just maybe he needs a little more than "a little engineering".

And yes OP, put the coffee on, call the Badger since he's in your backyard. One set of experienced eyes can tell you more in a minute then ten days of conversation on this forum (but it won't be nearly as much fun!) If his bill is more then what he can save you in fuel in one year it would be a surprise to us all.

You bring up another valid point. I am not sold that the off peak heater is saving me much of anything. When its gets really cold 0 degrees or more the gas heater will kick on to help out at night. Heck the gas heater kicks on once or twice to help out at night even at 30 degrees.

FWIW: R19 and R38 batts are the world's crappiest lowest density fiber insulation, and even if it were performing at it's labeled value, are at best current code-min for MN, and well below the IRC 2009 or IRC 2012 minimums. (MN is still at IRC 2006). Low density batts don't perform as-labeled unless at their full manufactured loft (6-1/4" for the R19), with air-barriers on both sides, and no gaps or compressions. R19s compressed into 5.5" 2x6 cavities are at-best R18, and that's if the installation is truly perfect. R38s in an attic rarely have a top-side air barrier, and suffer significant losses of performance to convective exchange with the colder attic air above. That's only "well insulated" in a relative sense, but nothing like a high performance building envelope.

The 14"-16" of cellulose in the older part meets IRC 2012 code min, if it's done evenly, and that deep all the way out to over the top plates of the exterior walls (probably can't, given that it probably has at most the ~11" of 2x12 joists at the eaves.)

A 6"overblow of cellulose on the R38s in the addition attic would be low money, and sufficient to keep the performance robbing convection through the low density fiberglass at bay, letting it perform at or near it's rated R, and you'd then be at IRC 2012 code min or maybe a hint better. But air-seal the ceiling first- infiltration losses lead to both energy loss and moisture problems in the attic spaces.

R19s in walls are a bit harder and more expensive to fix. Getting a dense-packing tube into the cavities is a PITA, but it can be done, and dense-packing either cellulose @ 3.5lbs density or new-school fiberglass @ 1.8 lbs density fills the cavity completely, eliminating convection currents around compressions in the batts, and eliminating 99% of the convection within the fiber layer, reducing the outdoor air infiltration to boot. You'd be at about a true R20 center cavity, which would make IRC 2009 code-min in southern MN (climate zone 6) but not quite in northern MN (climate zone 7). http://energycode.pnl.gov/EnergyCodeReqs/?state=Minnesota

Is the basement insulated and air-sealed at the foundation sill & band-joists at least? How about the basement walls? (Hopefully the heated slab is insulated?)

Whether there is any way to get enough heat into & out of the floor at reasonable water temps to fully heat the space depends on the actual heat load numbers. Getting rid of the rug will definitely help, but with an air-leaky addition with a lot of code-min window, maybe not. If it's a wood subfloor with extruded aluminum heat spreaders as the thermal link between the PEX tubing and subfloor, maybe. If it's just suspended tubing or tubing stapled to the subfloor without benefit of any heat spreader plate, it's very doubtful indeed (you may need water hotter than the rated operating temperature of PEX tubing.)

Before sinking thousands of dollars into getting more performance out of the radiant, fix the insulation, and consider supplementing the radiant heating for that addition with a mini-split. You can get about 15,000BTU/hr out of a Fujitsu AOU 15RLS2-H at or Mitsubishi MSZ-FE18NA @ -15F outdoor temps, at an efficiency nearly 2x that of your electric hot water heater. (Either would be less than 5 grand, installed, in my neighborhood, half that if done as mostly DIY.) And you would then have high-efficiency air conditioning as well.

Dana is right. There is no shortage of folks who will try to get your money into their wallet. Determine exactly what you currently have before determining what you need. Do a ROI analysis to determine how best to go forward and check the credentials of anyone you hire as many HVAC pros are far from that.

Posted By Dana1 on 22 Nov 2013 05:15 PM
FWIW: R19 and R38 batts are the world's crappiest lowest density fiber insulation, and even if it were performing at it's labeled value, are at best current code-min for MN, and well below the IRC 2009 or IRC 2012 minimums. (MN is still at IRC 2006). Low density batts don't perform as-labeled unless at their full manufactured loft (6-1/4" for the R19), with air-barriers on both sides, and no gaps or compressions. R19s compressed into 5.5" 2x6 cavities are at-best R18, and that's if the installation is truly perfect. R38s in an attic rarely have a top-side air barrier, and suffer significant losses of performance to convective exchange with the colder attic air above. That's only "well insulated" in a relative sense, but nothing like a high performance building envelope.

The 14"-16" of cellulose in the older part meets IRC 2012 code min, if it's done evenly, and that deep all the way out to over the top plates of the exterior walls (probably can't, given that it probably has at most the ~11" of 2x12 joists at the eaves.)

A 6"overblow of cellulose on the R38s in the addition attic would be low money, and sufficient to keep the performance robbing convection through the low density fiberglass at bay, letting it perform at or near it's rated R, and you'd then be at IRC 2012 code min or maybe a hint better. But air-seal the ceiling first- infiltration losses lead to both energy loss and moisture problems in the attic spaces.

R19s in walls are a bit harder and more expensive to fix. Getting a dense-packing tube into the cavities is a PITA, but it can be done, and dense-packing either cellulose @ 3.5lbs density or new-school fiberglass @ 1.8 lbs density fills the cavity completely, eliminating convection currents around compressions in the batts, and eliminating 99% of the convection within the fiber layer, reducing the outdoor air infiltration to boot. You'd be at about a true R20 center cavity, which would make IRC 2009 code-min in southern MN (climate zone 6) but not quite in northern MN (climate zone 7). http://energycode.pnl.gov/EnergyCodeReqs/?state=Minnesota

Is the basement insulated and air-sealed at the foundation sill & band-joists at least? How about the basement walls? (Hopefully the heated slab is insulated?)

Whether there is any way to get enough heat into & out of the floor at reasonable water temps to fully heat the space depends on the actual heat load numbers. Getting rid of the rug will definitely help, but with an air-leaky addition with a lot of code-min window, maybe not. If it's a wood subfloor with extruded aluminum heat spreaders as the thermal link between the PEX tubing and subfloor, maybe. If it's just suspended tubing or tubing stapled to the subfloor without benefit of any heat spreader plate, it's very doubtful indeed (you may need water hotter than the rated operating temperature of PEX tubing.)

Before sinking thousands of dollars into getting more performance out of the radiant, fix the insulation, and consider supplementing the radiant heating for that addition with a mini-split. You can get about 15,000BTU/hr out of a Fujitsu AOU 15RLS2-H at or Mitsubishi MSZ-FE18NA @ -15F outdoor temps, at an efficiency nearly 2x that of your electric hot water heater. (Either would be less than 5 grand, installed, in my neighborhood, half that if done as mostly DIY.) And you would then have high-efficiency air conditioning as well.

Interesting information and educating as well. I can't answer what insulation is in the walls. I did not build the home, the house is fully finished. (only the utility room ceiling is exposed) .The attic addition is vapor barrier- ed with faced R38 insulation The home was built in 1992- addition 2005 and it looks to have been ahead of the minimum code until the last few years. I will look into the additional insulation added in the attic. The R19 was applied to the basement ceiling joist space. I will look into finding a way into the walls without making a new project. I don't know how the sub floor tubing is ran or what was used for basement concrete insulation. Large cardboard pieces were used to support the insulation height in the attic for the cellulose in older part of the home. The depth maybe more then 14-16 inches but something more for me to investigate. I appreciate the information.

If the basement walls are not insulated the design heat load can be pretty high. A poured concrete wall is about R1, and every square foot of above-grade basement wall has the same heat loss of about 12-15 feet of R19- batt insulated 2x6 wall. If you have 18"or more of exposed foundation, the heat loss of the basement could be as high or higher than the space above.

Insulating a basement wall has to be done correctly to avoid creating moisture problems, since you have both ground moisture issues and wintertime condensation issues to manage. The most cost-effective way to do it is usually with 2" of unfaced EPS glued to the foundation (seams sealed with can-foam or duct mastic) and trapped there with a 2x4 studwall with UNFACED batts). Put a layer of EPS between the bottom plate of the studwall and slab to eliminate wicking of ground moisture into the framing, and through-screw it to the slab with TapCons or similar. Since it's not a structural wall, 24" o.c. spacing and single top-plates keeps the thermal bridging low. The "whole wall" R of that assembly is in the R18-R20 range, which cuts the basement heat loss to near-zero- probably dominated by the amount of window area. Air sealing the band joist and foundation sill is also critical- foamy sill gaskets all leak air (some of the best-in class EPDM gaskets do OK though), and since it's leak at the bottom of the "stack", any air leaks on the space above draw air in through the band joist & sill gasket leaks. This leakage is usually more than all of the window & door leakage combined in a typical home, and a significant heat load in a MN climate. (Sorry, but it's project, any way you cut it.)

If the facers on the attic batts are the top side, air leaks into the attic from the conditioned space become a serious problem, since that significantly retards drying rates from the fiber layer into the cold but dry vented attic above. Frost on the interior side of the facer cuts into thermal performance and creates mold conditions and if the air leaks are big enough, it can create rot conditions in the proximate structural wood.

a decent efficiency system only requires a supply temp of about 74 degrees

Is that really possible? I'm looking at 85F supply right now and it's about the lowest anyone around here has seen. Big discussion as to whether to bump it to 87F or not.... With overnight lows at 22F and with no occupancy on the home yet, I've got a Master Bath with a ginormous North facing window that can only get to 63F with a tstat setting of 67F. The unknown variable is that the towel heaters aren't wired up yet, so we don't know if that will handle the early-morning chill or not. The nice thing is that with full flow, the floors, showers and shower seats are toasty and warm. :-)

No, that is clearly NOT correct ICF...good catch.  I was thinking slab temps and NOT supply temps...and I will correct/edit that. I have been doing too much integrated passive solar and hydronic radiant floor heating system thermal mass design work recently which involves determining and controlling slab temps...  85F is a great supply temp and I suspect that your slab temp is likely close to 74F.  Sorry about that and thanks for pointing out my error.

We actually like to design our bathrooms and associated zones to run at a higher slab temp than our other rooms to generate exactly that comfort sensation that you seek.  Of course to do this without overheating the bathroom, the bathroom heat loss rate has to align with this increased upward heat flux rate.  So this comes down to be willing to accept a higher heat loss rate from the bathroom(s) than you would typically accept for the other rooms and overall building.  However, since bathrooms are typically a small percentage of the overall exposed heat loss area and associated overall heat loss rate of the building, this is typically a reasonable tradeoff to make.  It sounds like you may already have exactly this situation and hopefully you already have separate zone(s) for this bathroom.  BTW, we also believe in placing bathrooms on the north side of the building.  Yes, a heated towel rack is wonderful and depending on the supply temp, may heat a small bathroom or powder room by itself. 

Yeah, I thought the North side was a pretty good place for the bathroom until the architect put up that big window she couldn't live without., In retrospect, it will be the thing that allows us to have toasty floors in there, but I'm not sure designing heat loss into a bathroom just to get that is where you want to go. She did want the window for the exterior look, and it's nice to look up in the shower and see sky, but......