A simple project of finishing the basement has now opened up possibilities of converting my entire first floor to hydronic radiant heat along with the basement as well.

So here goes...

I currently live in a 2100 SF cape in MA, built in 2002. Six inch outside walls, and well insulated. I heat the house with a 4 section Utica cast iron oil fired boiler with 2 Unico high velocity air handlers. The first floor heat only, second floor heat and A/C. The 2 1/2 tons of cooling upstairs cools the entire house, so there is no need for an air handler on the first floor for A/C.

The boiler is designed as a cold start Utica Stafire 3 cast iron boiler with an Amtrol 41 gallon indirect DHW tank. I've been running the boiler at 140F high limit. To prevent short cycling of the monster boiler, we changed the burner head and nozzle to .65 gallon and added plate steel inside the boiler to cut down the interior draft due to the smaller nozzle. I have 4 taco circulators, hot water, first floor, second floor, and one for expansion not being used.

The first floor is 1100 SF (28*40), kitchen, dining, bedroom, bath, and a foyer that is open to the second floor. I have access to the joists from the basement. My idea is to rip out the Unico box and all the ductwork, run 1/2" pex loops in each bay, so that would be close to 1/2" pex @ 8" OC.  In the foyer, I was thinking I should double loop since it is a high ceiling and the front door has quite a bit of heat loss and an A dormer with a window above, also the staircase is there so no place for pex there either. That would give me 5 loops between 275' and 300' each. I was thinking of splitting this into 2 zones. The living room, bedroom, and dining rooms are carpeted (for now, hardwoods later), the rest is vinyl. This is just a first floor of a standard cape, nothing unconventional.

 - Would this plan sound like it can heat the first floor if I can run the water anywhere from 125F-140F?
 - What if I go geothermal down the road and then only 110F water will flow, would 1/2" pex 8" OC do the job there?

Next the basement, 520 SF to be finished. I'll be laying down 2*4 sleepers with 1 1/2" rigid insulation between, 24" OC with 3/4" T&G plywood as a subfloor. Then lamiated hardwoods. The walls are insulated and there is very little heatloss, so I really don't need a lot of heat to warm up the basement.

-  If I changed the floor insulation to 1" rigid and ran a single 300 foot loop of 1/2" pex @ 24" OC, would that give out enough heat to warm the basement for say 58F to 67F? I'm not worried about striping either, it's a basementl.             - Oh, one more thought, should I channel the rigid insulation so the 1/2" pex is not sanwiched too tight between the plywood and insulation? I don't want super squeaking noises from expansion against the rigid board.


Thanks,
Dane

no one can answer your water temperature question without doing your heat load, but I can say unless this is a superinsulated house, you would not do geothermal without heavy plates in those joist bays. even with them, it's iffy: geo is not capable of very high water temps.

If you put the pex IN the insulation, you are insulating your pex. not very helpful.

 I'm a bit concerned that you're running the high limit at 140F, which is usually the lower bound of "safe" (aka "warranteed") operation of oil burners, even cold start boilers to avoid corrosive condensation on the heat exchangers & flues.  Sure, your air-handler coils are oversized enough that it delivers the heat just fine at 140, but methinks you're in danger of drastically shortening the service life of the boiler.  Assuming a delta-T of ~25F on the coil (could be more, could be less- measure it) 165-170F might be safer. Measure the return water temp, and set the aquastats on the air handlers to not kick in until it reaches a temp where the return water will be 140F.

If you PREFER 140F at the coils, a thermostatic mixing valve with a boiler-bypass pipe can get you there too, and your distribution losses will still be low.

If you have documentation from Utica that claims it can be run this way, ignore my comments (but let me know,eh? It would definitely be new-news to me.)  On pages 10-12 of the installation & operation manual they take pains to illustrate the various methods of protecting the boiler from low temperature return water, but they don't seem to spell out what "low temperature" means in degrees F.  (I'm betting buried somewhere in the warranty it might though.  Unless they've made an amendment on the laws of physics or have a radical new design, that temp is 140F.)

What Rob said on the radiation design details- you don't know what water temps you'll need unless you've done a reasonable estimation of the heat loss on each room/zone.   In Charlton I expect your design day temp isn't too severe likely in the 0 to +5F range, but without knowing how fast the heat leaves the building envelope on design-day, we have no idea how much heat we need to pump in to calculate what temperature the water needs to be.

I'm guessing any 4 plate oil burner is at least 3x oversized for your whole-house load, even derated. My similar-sized 1920s-vintage house in central MA has a design-day heat load a bit under 30KBTU, whereas even derated your boiler is probably still north of 80K.  With the low-mass radiant radiation you're talking about (as opposed to slabs) you'll likely need to buffer it to keep it from short-cycling, especially if broken up into zones, making the load on any individual zone call an even tinier fraction of the boiler's output.  (We're not talkin' a lot of thermal mass here- there's only about 15lbs of water in a 300' loop of 1/2" PEX.)

Thanks guys for the input. I get it that it's hard to tell without a heat loss being done. I was hoping that if I said I had a cookie cutter contractor home, but with R19 in the walls and probably better than average insulation than a standard contractor built home, it might be able to get me somewhat of an idea, but I understand, there are so many variables.

Rob,
The geothermal is at best just a thought. I probably can install a mixing valve and set it for 105 and see what happens. However the basement zone, there will be a 1/2" of space between the plywood and the rigid insulation if I install the 1". I was just going to channel out about 1/4" deep by 2" wide area for the pex to lay on so it would not be pancaked so tightly, which I assume would cause a lot of noise during expansion and contraction. My original plan was to install 1 1/2", but not if I put the pex in, then it would be 1" so the pex would not be IN the insulation.
Please add more thoughts, I am just trying to learn here.

Dana,

I'm not sure about the warranty language, I'll have to check on that. However I clean the boiler every year and there is next to zero of anything on the water jacket. Even the Utica rep told us to install the 4 section and run the high limit at 140 for the hot water. That was their engineer's idea, along with putting the .65 nozzle and the F0 head in. They wanted plenty of 140 water to supply the Amtrol water tank without overheating the hydro air handlers. Many times in the summer, I see the boiler temp at 80F because there was no call for hot water. Why would they design a cold start (no low limit or standby temp) to do this if it was bad for the boiler? Steel, boiler, yes very bad, cast iron with steel nipples, very bad, but cast iron with cast iron nipples? Your guess is as good as mine, but I'll check on it. As for the flue and chimney, it is all stainless steel, no corrosion problems there.

Just a bit more info, This house was unfinished originally. So all of the 1st floor ceilings (second floor floors) have 10" insulation in them. The foyer walls above the first floor are all insulated as well. This may sound good, but since there is no heat flowing to the second floor through the ceilings like a normal house, the draft of cold air coming down the staircase is incredible. So I want to realy heat that foyer.

Also, I just want to make sure that everyone is clear, this is a cast iron boiler, 4 sections joined by cast iron push nipples. I'm not sure why 140 degrees for a high limit will cause trouble? It drops to 80 and maybe lower nearly every day during the summer because the hot water tank is not calling for heat. By design there is no low limit or standby temperature, so even if the high limit is 180, there is still nothing to prevent it from dropping to 80F daily when there is no demand for hot water. If it is a real issue, please let me know, I don't need to replace it, but after 8 years of service, there are no signs of any issue on the water jacket, clean as a whistle. Is it the interior of the boiler that will be a problem?

Thanks everyone!

when it is running, low temps cause condensation of the flue gases. the boiler has to get hot enough to prevent that and evaporate the condensate to avoid rusting out the boiler around the flue partition. that said, 140 is a pretty well accepted minimum for most boilers.. condensation occurs cooler than that, and I would guess that it's hotter in the flue in the first place, but I'm reaching a little there. I would chat with Utica about it though, it may even vary boiler to boiler.

I don't like much about this basement install, though it might work it will not be a low temperature application without plates and likely more than 24" o.c. coverage. If it's "just a basement" I'm not sure why you want to get it to 67 degrees in the first place?

Sulfuric acid will eat cast iron as hungrily as it will steel, and it's primarily the sulfuric acid in heating oil exhaust that's the culprit, but there's carbonic acid as well.   Even stainless won't tolerate sulfuric acid forever.  The barometric dampers dilute the exhaust prior to the flue, lowering it's dew point considerably. (The dew point is largely influenced by the CO2 concentration- the higher the CO2, the higher the dew point. With sufficient dilution it drops the dew point to under 100F.)

The real condensing temp for oil exhaust is closer to 130F, but when any part of the fire side of the HX is at that temp some condensation is occuring, which is why most build in some margin for themselves on the warranty front with 140F as the return water temp.  Cold start boilers still need to re-gasify/boil-off the condensate that occurs on startup, which means the average operating temp has to be above the exhaust's dew point.  Maybe that happens in your system with a 140F high-limit, but I'd be surprised.  Measure the return water temp at several points of time into a burn cycle then call Utica- they should let you know if you need to be running it with external boiler bypassing or some other means of low return-temp protection.

Some boilers have internal boiler-bypassing to limit the hazard and can tolerate somewhat lower temps, but it would be surprising if they could tolerate and average operating temp of 120F for less, unless advertised as such.  The Burnham Revolution gas fired cast iron beasts have a fairly sophisticated internal thermostatic pump control on it's bypassing and tolerates return water as low as 55F without condensation, but I've yet to hear of an oil fired cast iron boiler with similar low-temp tolerance.  When operated with return water temps under 120F the Revolution runs right on the hairy edge of condensation @ ~89% combustion efficiency, 87-88% AFUE (which is pretty much a theoretical limit for non-condensing gas-fired systems.)

Ok, probably not a good idea for 24" OC. We're on a tight budget but I do have an extra $1k to spend, that's why I'm asking about going to radiant. Since I only need about 1500 feet for the first floor, I would have an extra 300 feet of tubing if I bought two 900 foot rolls which would only be $65 more over buying 1500 feet. For the extra $65 i was thinking it would be better than nothing under the laminate flooring. I'd also save $200 by using the 1" rigid insulation instead of 1 1/2". I have all the extra parts hanging around to connect everything up, I just need a T-stat. All in all, i would break even at worst and have a fairly warm floor?

The new finished space is going to be a game/TV/play room, that's why i was hoping to get just a few extra degrees in there. There will be very little heat loss after I insulate everything and there is only 1 tiny basement type window. I'm wondering if that 58 degrees will move up a little after all is insulated. I'm sure the halogen MR16 lights in the ceiling will add to the temp a bit too along with some wall sconces. There is a 7" vent with a fan pulling air down from the pantry on the first floor to keep the air from getting stale.

I just think this is a good opportunity to get rid of that noisy Unico system, the blasting of warm air when it runs, then the drafts after it shuts down...tired of it. I got to say though, it cools better than any conventional system I've seen, so the upstairs AC/Heat unit stays no matter what.


As for the boiler, the last efficiency test i ran, the flue temp was 325, a tad bit low. For the annual cleaning, I always pull the hood off the top and swing open the burner door to clean the passage ways within the boiler. I have not seen anything in the way of condensation or residue from condensation building and drying. I am concerned though that there could be an issue of less than 140F return water? Is that a valid concern or is everyone thinking the condensation is the real killer here?


Thanks

Dana,

Ok, I just read your post now, that's the information that I am looking for. I was unaware that it's the Sulfuric acid in the condensation which is the problem. Apparently there could be condensation building up behind the target wall or somewhere in the lower rear portion of the boiler where the return water enters. See, I learned something today. I'll measure the return temp with both zones running as it hits the current high limit, then push the high limit up a little at a time until the return water is close to 140F. Looks like I'll be adding a mixing valve into the system.

Thanks

I did the heat loss on the first floor, 24k BTU loss. Looking for a chart to see if 1/2" pex @ 8" OC without plates will work at 140F.

Without plates you won't get there in a staple up. With plates, probably yes.

You're looking at 1100' minus whatever cabinets, furniture, stairwells, walls, etc you have in the way- call in 900' of clear floor area if you're lucky, which means you'll need ~25btu+/square foot on design-day (24000btu/900')

You can get that out of 140F water with extruded plates, figure on half that at best, unplated. For a typical heavier-duty plate performance, see the graph at the end of this document:

http://www.houseneeds.com/Shop/manuals/ctrack_installguide.pdf

Unplated you'll be a bit below the line where you have R3 above the plated floor. With sheet metal plates you might squeak 18-20BTU/ft out of it, but unplated you'll have to run it at 180F or more on design-day.

You can't cheat the physics- you need surface contact to conduct the heat out of the PEX, otherwise it's just going round & round in your loops hangin' on to it's heat. Embedded in concrete contact area is excellent, hammered into extruded plates the contact is pretty good. In thin plates it's not terrible, but in a wood channel or suspended below a subfloor the PEX is surrounded by an insulating boundary layer of air, and you're counting on convection & radiation for the heat transfer, which is much less efficient, and therefore needs a bigger delta-T to achieve the same transfer rate.

If you really can't bite the bullet on plates, you can come close using outdoor-reset controls on the high-limit or mixing valve to crank up the temp when it's actually cold. PEX can handle up to 200F (Wirsbo has a 200F test that's been running a quarter century now) but isn't usually rated for over 180F. If your heat loss was calculated with Manual-J or similar it's likely to be overstated by ~25-30%. A better way to determine the true heat loss is with correlated fuel use & degree-day history (which is a measurement, not an estimate.) Odds are you really only need ~20-22btu/ft.

(For reference my ~2000ft house in Worcester has a measured whole house design-day heat loss of a bit under 30K, but it's an antique, with known insulation gaps and 2x4" construction, no insulating sheathing, not "well insulated", more like "way better than non-insulated, but has more work to be done".)

But see if you can't find some room in the budget for at least some cheap plates and outdoor reset control on the mixing valve- then you'll have some margin, and it might even work. No way are you getting all the way there without either plates or maxing out the rated temp of the tubing.

Well, here is some good news, we are running the boiler at 160, not 140. I taped and insulated a meat thermometer to the cast iron return. First I depleted the hot water, then turned on both heating zones. The return went down below 100 until the supply water made it around the loops. The as the burner heated, the delta -t increased to as much as 35 (155 to 120). As soon as the boiler hit 160, off went the burner and the delta -T closed to 20. The boiler cycle was 14 minutes, a nice steady run. It turned on again exactly at 140, a 20 degree differential.

So i think that the delta - T will be less with the radiant as there is no way radiant tubing can put out the heat that these air handlers can.

Anyway, I am going to do a more comprehensive room by room analysis tomorrow with a couple of different heat loss calculators. Just remember, I have a fully heated second floor, and i did not figure it that way when I did the first heat loss calculations.

Rob and Dana. thanks for the assistance, I'll update my progress.

I used 2 heat loss calculators,
1- build it solar http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm
2 -Warmly yours http://www.warmlyyours.com/hlc/room/index_main

I'll list the rooms/ floor SF then Builit it Solar BTU and WarmlyYours BTU

Bedroom 165 SF 2689 BTU 3578 BTU
Living 216 SF 3319 BTU 3765 BTU
Bath 70 SF 989 BTU 1525 BTU
Foyer 44SF 4044 BTU 4733 BTU *** there are 2 FHA vents in this ceiling from the 2nd floor zone all I can do is double loop and plate
Kitchen 256 SF* 5047 BTU 6567 BTU * 256 SF - 56 SF of counter/stove/refrigerator space.
Dining 176 SF 3044 BTU 4132 BTU

total 927 SF 19132 BTU 24300 BTU

Degree days have been 6733 and 6886 for 2007 and 2008 here. I have a weather station to figure that for me.


So if I figure unplated, maybe 12 BTU/SF @ 140
thin plates = 18 BTU
extruded = 24 BTU?

What about 160 F?

I might use the average of the two calculators per room for my heat loss.

I think I'm good if I can get the BTU S/F @ 160 F figures for the unplated/thin plate/extruded plates

Thanks again!

P.S. I do have a 70K BTU wood stove on the utility side of the basement that heats the whole house pretty much, so we won't be cold. I just need to figure if the radiant will heat the first floor without the stove running.

are you figuring for carpet or for wood?

with carpet you're SOL in several of those areas.

I would almost never recommend running a 160 degree radiant system if you can avoid it. while your boiler may not go any lower, using a mixing system with reset can still run the system far more efficiently, especially during shoulder seasons. the reason being you would not have to fire the boiler on every demand: if you only need 100 degrees, and your boiler is still 140 from the last demand, you can draw significant heat from the boiler before having to fire it again. without that, it just bounces off the high limit, then when you lose your demands, all the heat in the boiler just bleeds out to the mechanical room.

under wood though the 140 number for extruded, light, no plates is about 30 BTUs/sq ft, 19, 15. 160 about 36 (too much for wood floor), 24, 20.

Rob,

Currently a split of vinyl and carpet. But it will be all wood and tile soon. I can add a mixing valve, or boiler by pass to reduce the system temps to 140, even lower for the wood areas if needed. Oil fired cast iron boilers are what they are, there is going to be extra heat bleeding into the room because you can't run them very low, I can deal with that. That's what happens all summer long when heating hot DHW water. And at some point, those are variables that can be changed down the road. (gas condensing unit and hot water heat pump are the probable candidates)

My concerns are getting rid of the Unico system, and installing enough pex tubing properly to heat the first floor without any assistance of the wood stove on a 0 degree night. We will be sheet rocking 1/2 of the basement ceiling and once that is done, it is done. I may buy plates for the areas that will be sheet rocked, then add the rest later when I get more cash, The unfinished side is where the boiler and wood stove reside, so we won't be cold.

Oh, I am assuming that these BTU figures are good for 1/2" pex @8" OC?

basically any size pex at 8" o.c. yes.

You said you have a cold start boiler. that means it is not sitting there hot all the time. you can choose to reduce its cycling by using a reset mixing valve and lower water temperatures and reap the efficiency benefit. Or not. I would strongly encourage it if this configuration is going to sit more than a couple of years, and if you are thinking you will EVER use low temperature heating like a gas condensing boiler, heat pump, or the like, you should be using heavy plates pretty much everywhere. Otherwise you're looking at supplemental heat, demolition, or abandonment of the radiant system in that future configuration.

You make your priorities, that's fine, but your language indicates you are thinking of the future at least a little, and putting in naked pex is not setting you up for where you want to go.

Yeah, It looks like naked pex ain't gonna cut it. I'll fall short, for the most part only providing only about 70% of the heat needed and that's at 140F.
Those plates put it WAY out of budget though. I'd go from $900 to $2700 in a snap. I could run double the naked pex and manifolds and still be $900 under vs using plates.



Champagne taste on a beer budget!

You could triple the tubing, and it wouldn't really help.

Hmmm, maybe when I do put hardwood and tile in, then I can run something on top of the sub floor. It might be better to wait...but now I gotta box in all that ductwork in the basement...arg.

I did it anyway and it is working BETTER than planned!