New Home, Hydronic Heating Questions

RedNeckRacin

Howdy all, First time poster, short time lurker. I have been working on building my house myself this summer and I'm getting close to needing to install my heating setup. I have been reading everything I can find on hydronic heating and I'm somewhat sure of what I need but I wanted some feedback from the experts.

Design info: House is a 2 story, 2x6 R-21 8' wall, 24x40; total SF of 1920 over an insulated basement with a walkout door. The basement floor has 3 loops of 1/2" pex of around 300'. The slab is insulated by 1" r-5 xps. The basement walls are superior walls with an r-12 and 9' height. The garage has a 4' r-12 frost wall and is also insulated with 1" r-5 xps with 3 loops of 1/2" pex of around 300'. The walls are 2x6 r-21 and are 10' high. The house shares a wall with the garage. Both attics will have r-38 insulation with raised heel trusses. I used a Manual J calculator from coolcalc.com and came up with just under 58k btu/h for my design load. That is not including the garage which when I ran the calc with the garage I was looking at around 90kbut/h. So I'm thinking of a mod/con Lochinvar 120k btu/h boiler.

Anyways, I have been trying to figure out how to layout my hydronic system to heat the house and I'm looking for a bit of guidance on that. Everything I have read says to put a full loop between the joists, to use pex-al-pex, and heat transfer plates. The problem is that when I take the 58k btu/hr and divide by the 1920SF I get a required output of around 30 btu/hr/SF. This seems like a high number and looks even more daunting considering I have 3/4" sub-floor and I intend to carpet 80% of the 2nd story and about 30% of the first. I am assuming that I need to insulate the joists in the basement to force the heat into the 1st floor. So I guess my questions are: Is running enough 1/2" pex between the joists with heat transfer plates to give me 8" spacing(full loop per joist bay) enough to heat the first and 2nd floor? I am not planning on installing the pipe on top of the current sub-floor.

Is there anything that I'm missing?

EBEBRATT-Ed

I don't claim to be a radiant guy at all so someone with more knowledge will have to chime in.

But, if you can't get enough heat in with radiant tubing you may have to add something else in to help out.:
baseboard, air handler, panel radiators etc

RedNeckRacin

That's part of my question, is there a good resource for the btu output for the specific size and spacing I'm looking at? (1/2" pex looped for 8" spacing between joists under a 3/4" subfloor with varying floor coverings) One manufacturer had 1/2", 5/8" and 3/4" pex all producing the same btu/sf which I didn't think was correct.

kcopp

You need to get a proper heatloss done. A plumbing supply house or contractor or a system designer will do this for you.

Jamie Hall

RedNeckRacin said:

That's part of my question, is there a good resource for the btu output for the specific size and spacing I'm looking at? (1/2" pex looped for 8" spacing between joists under a 3/4" subfloor with varying floor coverings) One manufacturer had 1/2", 5/8" and 3/4" pex all producing the same btu/sf which I didn't think was correct.

There really is only one variable in radiant work -- how hot can you get the floor? That is what determines the heat output from the floor. 30 BTUh/sq.ft is pretty high, as you note -- and may be very difficult to achieve without an uncomfortably hot floor -- or overheating the layers underneath those carpets. The size of the pipe -- assuming that you are using heat transfer plates -- is almost irrelevant to the heat output, although it will affect the sizing (and cost of running) the necessary pumps.

hot_rod

Agree, you want a room by room load calc and system design that show required supply temperatures to every zone.

There are times when radiant floors alone will not cover the heat load in some rooms. Carpet is not your friend with radiant , and rooms with a lot of cabinets or furniture can limit floor output. Approach with caution!

Harvey Ramer

Everything you've described about your building construction suggests your heat load calc is out in left field. Well, unless you live in the Artic circle. What is your outside low temperature design point?

RedNeckRacin

Harvey, I'm in Clearfield County PA and my winter design temp is 0 degrees Farenheit.

HotRod-I am starting to realize this but the more I'm reading the more my heatcalc seems to be off. A gentleman on here had a house with 2x4 walls with more square footage who had a similiar btu design load as I did for a house built 25+ years ago which seams strange to me. I did the best I could with the coolcalc.com website but I didn't realize it was off, from what I heard as much as 25%.


Jamie-Good to know about the heat transfer plates, I was thinking of running 1/2" 8" on center with the plates. That makes more sense why they lump the 3 different sizes lines together then.

kcopp-I'm more of a DIY guy. Is there an online calculator or a pdf that I can fill out myself? I'm more than capable of doing design calculations if I have a good reference material.

As of right now, the walls are 100% empty, no boiler, and only the slabs have tubes ran. Thanks all for the comments so far!

Harvey Ramer

My go to for radiant design loads are Uponor ADS, which is free, and Loop Cad which I paid a lot of money.

hot_rod

RedNeckRacin said:

Harvey, I'm in Clearfield County PA and my winter design temp is 0 degrees Farenheit.

HotRod-I am starting to realize this but the more I'm reading the more my heatcalc seems to be off. A gentleman on here had a house with 2x4 walls with more square footage who had a similiar btu design load as I did for a house built 25+ years ago which seams strange to me. I did the best I could with the coolcalc.com website but I didn't realize it was off, from what I heard as much as 25%.


Jamie-Good to know about the heat transfer plates, I was thinking of running 1/2" 8" on center with the plates. That makes more sense why they lump the 3 different sizes lines together then.

kcopp-I'm more of a DIY guy. Is there an online calculator or a pdf that I can fill out myself? I'm more than capable of doing design calculations if I have a good reference material.

As of right now, the walls are 100% empty, no boiler, and only the slabs have tubes ran. Thanks all for the comments so far!

Find a load calc program that is specific to radiant/ hydronic designs. Most all the radiant manufacturers have free copies or will provide a load calc for a small fee.

I think LoopCAD has a free 30 day trial. It is Windows based, so if you run a Mac beware you need a Windows emulation software and the manufacturer claims they have not tested or do the support those programs.

Ironman

Modern building codes have required for 20+ years that a house be constructed so that it has less than a 25 btu per sq. ft. heat loss.

I agree with everyone else that your calc is off. You need to do a room by room. One certain room that has a vaulted ceiling with a lot of glass and can lights, may require over 30 btus per sq. ft. But that shouldn't be true for the entire structure.

Best case scenario for a floor using good extruded heat transfer plates is 18 - 20* output at a reasonable SWT. The more wood thickness and carpet above the plates, the less output because of their higher R value. Try to keep the R value well below R2 on floor coverings (including the subfloor).

Don't upsize the boiler! That's on of the worst mistakes made in heating. If your heat loss actually was 90k btu, then you should choose the closest size boiler available. In that case, I'd probably choose the 85k KHN. There's a 10 -15% cushion built in to load calc programs; and even if 90k was an accurate figure, you're only going there on the coldest night of the year. The outdoor temp will rise with the sun and the internal heat gain in the house along with its mass will keep the inside temp from dropping significantly, if at all.

Also, don't try and create a lot of zones unless you want to add more complexity and costs which are not necessary. Keep the zones minimal.

RedNeckRacin

Ironman said:

Modern building codes have required for 20+ years that a house be constructed so that it has less than a 25 btu per sq. ft. heat loss.

I agree with everyone else that your calc is off. You need to do a room by room. One certain room that has a vaulted ceiling with a lot of glass and can lights, may require over 30 btus per sq. ft. But that shouldn't be true for the entire structure.

Best case scenario for a floor using good extruded heat transfer plates is 18 - 20* output at a reasonable SWT. The more wood thickness and carpet above the plates, the less output because of their higher R value. Try to keep the R value well below R2 on floor coverings (including the subfloor).

Don't upsize the boiler! That's on of the worst mistakes made in heating. If your heat loss actually was 90k btu, then you should choose the closet size boiler available. In that case, I'd probably choose the 85k KHN. There's a 10 -15% cushion built in to load calc programs; and even if 90k was an accurate figure, you're only going there on the coldest night of the year. The outdoor temp will rise with the sun and the internal heat gain in the house along with its mass will keep the inside temp from dropping significantly, if at all.

Also, don't try and create a lot of zones unless you want to add more complexity and costs which are not necessary. Keep the zones minimal.

I have no vaulted ceilings and minimal glass. I have a total of 17 windows 4 of them are 3x3 (2 double hung, 2 casement) and the rest are 3x5 (Pella 350 series for all). I had to add in the garage to get the 90k estimate. I was worried when I divided the 58k btu (house load including basement) by the floor space and got over 30btu/hr/sf. If I add in the basement area, that number drops to 20 btu/hr/sf. I was planning on keeping the basement a little cooler so maybe I shouldn't ignore that for my heating load....

Does the Uponor ADS do a room by room calc?

Ironman

I was giving that kind of room as an example to show that a particular room might need over 30 btus per sq. ft, but the entire house shouldn't.

RedNeckRacin

ok, so I found my error, 54k was with the garage on the coolcalc website, I had all the menu's collapsed and overlooked that. 23.3k is what the house is calling for. WHEW!

Steamhead

And don't forget, you probably don't need to heat the garage to the same temp as the rest of the house.

RedNeckRacin

Steamhead said:

And don't forget, you probably don't need to heat the garage to the same temp as the rest of the house.

You are correct sir, I was planning on only heating it to around 62 degrees or so.

PinkTavo

OK. This is a little apples to oranges, but I have a 2000 sf place with 3-wyth brick walls (no insulation) and R-30 in the attic. One story. I have steam heat with 208 EDR based on measuring the radiators. 208x240= 49920 BTU. My house is ALWAYS warm even at -10 degf it stays about 72 (design temp is 0 degf in my area), which rarely happens.

I think you need a better heat loss calculation.

Sorry...I see you did....site won't let me delete, only edit.

RedNeckRacin

So I have been doing a little more research and pondering as well. I want to use a lochinvar boiler(local hvac and plumbing supply sells them and I get a discount). The smallest one that will work with DHW would be a CCN120. This is about twice the size that I need but the DHW is very attractive to not have a hot water heater. I am concerned that the low fire rate of 24k btu is too high for this setup though. The house itself only requires about 23k btu on design day. Because of this, a CDN070 with a low fire of 13k btu seems to be much better sized.

Also, I am thinking that I can vary the heat transfer plate spacing to modulate my heating output enough to heat the rooms adequately, However, since the output required is so low, I think that 3 zones in the house would be the max reasonable. (one per floor and one in the basement slab) plus one zone in the garage.

Am I rambling or does that all make sense?

Ironman

Size the boiler to the heat loss of the house, not to the indirect! Even the smallest indirect with the smallest boiler will produce far more hot water than the same size gas water heater. If you're gonna have something that requires an unusually large amount of hot water, such as a hot tub, then increase the size of the indirect, not the boiler.

The boiler sizing numbers in the literature for indirects is only there to show how many btus are needed to get the rated output; they're not a requirement.

Oversizing a boiler for an indirect is a common mistake made by those who are not versed in designing systems.

Zman

I would strongly recommend going with a properly sized boiler and an indirect. The mismatch in sizing between demand hot water and space heating is always the issue.
If you want to explore the whole combi boiler option, you will need to evaluate your hot water needs. How many fixtures and what flow rates would be a start...

delta T

Agreed, I have yet to see a single situation where a combi boiler is properly sized to handle both DHW (high demand) and space heating (low demand). 23kbtuh is your heat loss, chances are for instantaneous hot water generation you will need something in the neighborhood of 150kbtuh or higher to handle the DHW needs of an average household. That discrepancy will mean either not enough DHW production or a boiler that will shortcycle itself to death in short order trying to fulfill the space heating requirements. If space is the consideration, maybe consider a separate on demand water heater for the DHW.

I know it seems like you save some money on buying a combi unit, however the increased wear and tear on an oversized condensing boiler will mean a higher maintenance cost over the course of the boiler's life, which will now be greatly reduced.

RedNeckRacin

I was attracted by the possibility of not having a hot water tank what can I say? I knew it was oversized by a good margin and likely more so by the fudge factors in the manual J. I guess I'm going to look at an on demand DHW heater then.

gschallert

Ironman said:

Size the boiler to the heat loss of the house, ...

Just out of curiosity, what would be a good boiler for such a small heat loss? 23K is needed on design days only so what would fit that wouldn't short cycle to death.

RedNeckRacin

a lochinvar CDN040 has a low fire rate of around 8k btu, that would seem to be about right. I have a garage to heat with 3 10' wide doors so I'm a bit gun shy about sizing right at the edge. Part of my heat slab extends out underneath the doors.

delta T

RedNeckRacin said:

I have a garage to heat with 3 10' wide doors so I'm a bit gun shy about sizing right at the edge. Part of my heat slab extends out underneath the doors.

Did you account for this in your heat loss? If you want a little fudge factor, a KHN055 will give you more room on the top as compared to the CDN040 and will modulate down to 5500. Might be worth consideration, though the price-point is higher and it sits on the floor instead of hanging on the wall (though it does have a pretty low profile).

FWIW, I would seriously consider using a sidearm tank if you have the room. On demand water heaters are nice, but it may take some serious renovation (usually a new gas line and flue) to get it installed. There is also a significant amount of maintenance required to keep them in good working order. A stainless steel indirect water heater will need little to no maintenance (though your boiler will regardless, adding an IDWH will not change this) and should last a very long time as long as your water quality is not horrible. Installed cost of an IDWH will likely be close to, if not less than an ODWH but without the need for maintenance.

If space is really the deciding factor and you will not be able to fit a tank, then an ODWH will be the way to go. I would not install a combi boiler with a heat loss that is that low.

gschallert

RedNeckRacin said:

a lochinvar CDN040 has a low fire rate of around 8k btu, that would seem to be about right. I have a garage to heat with 3 10' wide doors so I'm a bit gun shy about sizing right at the edge. Part of my heat slab extends out underneath the doors.

So what's the heat loss of the garage? I'd also recommend an indirect stainless tank, love mine. If you use a lot of hot water back to back size the indirect capacity up don't bump up the boiler. What are your DHW needs? How many people in the house? How many bathrooms? How many feet is the furthest point of use?

keyote

I was able to download a free 30 day trial of loop cad that gave me the heat and cooling load calcs while allowing me to play with the loop design it gives you all the information you will need changing as you changes design like flow head water temp surface temp etc. it still works after 30 days but the changes made after 30 days dont stay when the program is closed and you can no longer export files. it was really easy to learn to draw with they have videos and instructions id do as much of that before the download clock starts. That said id say your loops are a little long i know 300 is a common rule of thumb but its a max and not ideal for several reasons maintains a consistent delta t is one but also it pushes your head flow ratios to a place where pump choice gets less than ideal.The other comment Id make is yes definitely plates but depending on your choice of flooring consider radiant ceilings instead. nailing hard wood is very difficult over radiant then you have the issue of surface temp which with your insulation probably wont be an issue but might, and finally leaks under hardwood are a disaster and people cover the floors up with stuff that can interfere with the heat. theres a co that makes a neat graphite plate embedded in foam boards thats cheap im going to use for the rest of the house on the ceilings, you will also want a 10-1 modcon boiler to be able to go low enough for your low loads i love my KHN085 mod cons work most efficiently when in the low end of their modulation so the lochinvar 085 and 55 both mod down to almost the same 8kbtu i went with the 085 for that efficiency and the ability to expand an addition and the better for the indirect hot water tank.
dont think you need the alumapex just an oxygen barrier pex

keyote

RED
you may not have considered this I didnt its not the cold design day that usually the problem its a boiler that can do the rest of the 364 days efficiently thats usually about half and even less in the early fall and spring, the LOchinvar KHNs mod down to 1/10 of rating still putting out 97 % efficiency very few boilers can do that so if your 23kbt design day you might be at the KHNs 8 kbt you on a fall day, this is also something I had to contend with when i want to zone every room the loads on a single room especially on a warmer day might be less than the lowest modulation of any boiler, buffer tanks and things get around this but its another expense and complication. I can tell you with only one manifold on the 085 and piped without primary secondary or a buffer the boiler can mod down on the warm day just fine and still roar up to 100% and heat a 60 gallon indirect in about 2 minutes
also you cn set the boiler up with different supply temps for say snow melt or a shop but that involves mixing valves the boiler though will control them

RedNeckRacin

Delta T- Yes I did account for that in my heatloss. I went back to the coolcalc.com Manual J and doubled checked all my numbers, My house numbers went down a bit but when I when I was going through room by room and printing a pdf report on them my garage numbers got really strange. The program calculated my gross wall area as over 11,000 SF which it is not. 32x40x10 building size with a shared wall with the house on the 40 foot side butted up to the 24 foot side of the house. I went to print the pdf sheet off and saw the number error and I back calculated that for my 2x6 r-21 wall it was figuring around 4.55 btu/sf loss. So I figured out my wall area including the area of the doors (the program calculated this area correctly) and I came up with around 1440SF*4.55 btu/hr = 6552 btu/hr loss through the walls which was much more reasonable than 72k. Ill post up the numbers I got room by room here later, someone has to build this own house today....

Thanks for the thoughts gents, I'll try and answer any questions that I skipped later.

Gordy

@RedNeckRacin where are you at in your construction phase? Roughed in, Drywall hung?

rick in Alaska

Delta T:
Did you account for this in your heat loss? If you want a little fudge factor, a KHN055 will give you more room on the top as compared to the CDN040 and will modulate down to 5500. Might be worth consideration, though the price-point is higher and it sits on the floor instead of hanging on the wall (though it does have a pretty low profile).

As far as I know, the 055 is still just a 5:1 and only goes down to 8300 btu. Unless they have changed it to a 10:1. That is why I like the KHN085. It has the same low end, but able to make domestic hot water with the upper end.
Rick

delta T

You are correct, I misread the website, the low fire for KHN055 is 7,790 output, low end of KHN085 is 8,075 according to this:

http://www.lochinvar.com/_linefiles/KHN-PS-01.pdf

Thanks for catching that

keyote

The last KHN info is correct another thing I liked was Gordy put a lot of charts up about the efficiency curves on mod cons and basically they are most efficient when modulating down the most, even more so in radiant low water temp situations. so although I only needed 52 kbtu on design day maybe half that on average using the khn085 i will be down in the most efficient bottom third sweet spot almost all of the time, and get the extra capacity for DHW and whatever else i never priced the 055 but i bet is close to same price.

RedNeckRacin

Gordy said:

@RedNeckRacin where are you at in your construction phase? Roughed in, Drywall hung?

Gordy, I'm at the rough in phase. Just set my last exterior door saturday and still hanging some siding.

Do all of the Knight boilers have DHW? I don't know why I was only looking at the cadets...

RedNeckRacin

ok fellas, here is the room by room report on the house. I think the garage numbers are a little off, but the website isn't being completely cooperative. Also, to get my SF to work out, I had to add some area to the stairs. I think thats all the quirky things that I ran into. Also, I added closet space into the room that it was in.

Ironman

RedNeckRacin said:

Gordy said:

@RedNeckRacin where are you at in your construction phase? Roughed in, Drywall hung?

Gordy, I'm at the rough in phase. Just set my last exterior door saturday and still hanging some siding.

Do all of the Knight boilers have DHW? I don't know why I was only looking at the cadets...

All of the knight boilers will do domestic with the addition of an indirect tank. This is the way you wanna go. Forget about a combi: it's a poor choice for your application.

RedNeckRacin

@Ironman Thanks. that's the sort of direction I am looking for. Any recommendations on brands or setups to look at? I am going to have a dishwasher, kitchen sink, and a full 2 bathrooms that could potentially use hot water.

Ironman

Since the KHN 085 has about the same bottom end modulation (8k btus) as the 055, you could use that with a 30 - 40 gal. indirect and you'd have more hot water than a 50 gal. gas water heater would give.
You may also want to look at the HTP UFT085. It also has a fire tube HX and 10 to 1 turn down at a lower price point than the Loch because of less complexity.

keyote

My KHN 085 heats a Triangle tube 50 gallon in about 3 minutes after a long shower, i cant make that system run out of hot water. Lochinvar makes its own indirect and you can look into tanks that have extra ports for solar

Gordy

A few things to keep in mind for the wallet. You have chosen a fine company with lochinvar, and their condensing boiler line up.

Each line of Mod/con has its advantages over the other. So what advantages do you need, and what ones will you not need becomes a question.

The KHN is the top of the line up with 10:1 turn down ratio, and a whole bunch of other bells, and whistles in its control strategy.

Next step down is the WHN its a wall hung with a 5:1 TDR. similar controls as the KHN

Then there is the CDN, and the KBN both have a high head HX verses the Fire tube HX if the WHN, and KHN i would stick with the fire tube HX.

Go to lochinvars website and read the literature, and sizing for all lines. Look at the controls of all lines. All come with outdoor reset which is a must.

How many different water temps will you need to control in various zones? are they all the same water temp?

One determining factor will be the difference if any in floor coverings of the different zones. Another will be the zones heat loss.

Try to keep your zones at the very least to the min. modulation of your boiler selection. I would even go higher. This is because at design temp meeting minimum modulation of the boiler will be very different then the warmer times of the winter which will lead to short cycling.

The reason I asked where you are at in the construction phase is this. Give a hard look at radiant ceilings. You do not have the draw back of high R value floor coverings killing the output. Or furniture, and cabinetry taking away from available output SF.

Save the floors for bare foot areas of tile etc. Baths, kitchens etc. You could even do both if you need the extra btus for the load.

RedNeckRacin

@Gordy Should be 4 zones, garage, basement, first floor, second floor, So that should be two temperature zones (slabs vs subfloor). I should have only tile and carpet for the different floor coverings. Slabs will not be covered.

I thought about the ceilings, but the idea of warm floors really appeals to me. Also, I was planning on insulating between the floors anyways to help with noise reduction. I know its more efficient to heat the ceiling but I think the attachment to the floors is more permanent if that makes any sense. I was considering adding extra tubing for the bathrooms and kitchen possibly.



Any thoughts on a storage tank? Positives or negatives?