Adding radiant heat to existing hydronic baseboard heating

Discussion in 'HVAC Heating & Cooling' started by Thetruck454, Apr 16, 2018.

  1. Thetruck454

    Thetruck454 New Member

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    I want to add radiant heat to my hydronic heating system, but I’m not exactly sure how. The attached drawing is how I think it needs to be done, but I’d appreciate some input. I can’t get over the fear of a leak with radiant heat between the floor and subfloor so I’m running pex on the underside of the subfloor (unfinished basement) with heat reflective panels. The boiler outputs 150F-180F water and I’ve been told I need to drop that down to ~125F for radiant. I would use a relay to power the second circulator that only energizes when that zone valve opens so the circulator doesn’t run all the time. Is there a simpler way to do this or am I missing something else I need? Can I get away with a 3 way mixing valve and a monoflow tee on the cold side of the radiant heat or do I need the 4 way as shown?

    Sorry for the questions, I’m learning as I go with this.
     

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  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    That's similar to my system, but the installer put the pump before the mixing valve. You also want to add either a check valve, or use a circulator with a built-in one. Staple-up may require more heat verses where the pex is embedded in the floor, and adding insulation beneath the floor is quite beneficial as well. You'll also want a drain/purge valve(s) in there. Depending on the diameter of the pex tubing you use, you don't want any one run to be longer than about 200', so you may need more than one branch. IF so, then you may need a valve so that the flow can be balanced between them. An IR sensor can help to check the relative temperatures to aid in balancing them.
     
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  4. WorthFlorida

    WorthFlorida The wife is still training me.

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  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Also, regarding a thermostat for that room(s)...you may want to utilize a floor sensor. If you choose an air temp sensing one, some of them also incorporate the ability to sense the floor temp. Radiant floor heating has a much longer response time than air, so the heat actually must be turned off before reaching the desired set point so you don't get huge overruns...IOW, before the actual desired temp is reached, since it takes awhile for the heat to stabilize. Even with the pump off, the hot/warm water in the tubing will continue to provide heat. You'll also find that you may not want to use setbacks unless you're willing to wait a long time for things to heat back up. Convectors respond quicker. You'll have fair amount of mass to heat up to get the floor an actual radiant source, and since you won't have as large of a delta T to do it, it will take longer. In something like a cement slab, it could take days, but with wood, it's more like hours. The actual floor surface temp will likely be only in the low 80-degree range, if that, depending on how drafty and how well the room is insulated.
     
  6. Dana

    Dana In the trades

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    There are a lot of ways to do radiant, and it doesn't always have to be mixed down.

    Ultra-Fin convectors is just one way to DIY it with a high temp /no mixing without spending a lot of money or risking frying your feet:

    [​IMG]

    The "heat reflective panels" have no place in a radiant heating system. Most of the heat transfer with staple-ups is conducted. With suspended tube (or suspended tube enhanced with Ultra-Fin convectors) most of it is convective. What you DO need is real insulation to isolate the heat from the zone below. R11 is fine if it's above fully heated space, R20 if it's an unheated uninsulated basement, R30 if it's above a vented crawlspace.

    With staple-ups with aluminum heat spreaders (extruded or sheet metal) the insulation should be snugged up to subfloor. With suspended tube there needs to be at least a couple inches of clearance between the tubing and insulation, as well as between the tubing and the subfloor to allow the convection to occur.

    With suspended tube there is a modest improvement in zone isolation with a heat reflective surface on the top side of the insulation, the side facing the tubing & subfloor, but it's not worth spending extra on.
     
  7. Thetruck454

    Thetruck454 New Member

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    What if I were to go with just a kickspace heater for the bathroom instead since I’m not sure I want to keep a steady temperature? With monoflow tees that should integrate with the baseboard fine. The bathroom is 64 sq ft with the only outside wall being 7’x8’ which has a small 1.5’x3’ window. There is a single 32” door into the hallway. Walls are R-19 and ceiling is two layers of R-30. Currently it has 4’ baseboard which according to spec is only 1600BTU/hr (using 160F water). Online calculators say I should have ~ 3200 BTU/hr. Myson and Becon Morris makes small kickspace heaters which are ~3000 BTU/hr (using 160F water and low fan speed). I planned on making the bathroom it’s own zone with radiant so I’d do that for the kickspace heater as well. The next size up kickspace heaters from are 4100 and 5960 BTU/hr (using 160F water and low fan speed) which seam overkill for the bathroom.
     
  8. Dana

    Dana In the trades

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    What online load calculators are you using? Even if it were a corner bathroom where 2 of the walls were 2x6/R19 it wouldn't have a heat load of 32oo BTU/hr even at -10F (probably colder than your design temp) unless you keep that tiny window open! Even the 1600 BTU/hr of baseboard is overkill if kept at temp all the time, but it would be slow to heat it up on the coldest morning of the winter from a deep overnight setback.

    With UltraFin and 150F water you'd be able to get at least 25 BTU/hr per square foot out of the floor into a 70F room. At 180F it'll be more like 40 BTU/hr per foot. Assuming only 30 of the square feet of is available after deductions for the toilet, cabinets, etc (it's fine to heat directly under the tub too if you like, but not the toilet, lest the wax seal melt) that means you can get 750-1200 BTU/hr out of the floor.

    The U-factor of a typical 2x6/R19 16" o.c. wall is about U0.077 BTU/hr per square foot per degree-F. You have about 5 square feet of presumably at most U0.6 window, and about 50 square feet of wall. The U-factor of the ceiling is ridiculously low- too low to matter. At -10F outdoors, 70F indoors you have a temperature difference of 80F.

    Wall losses:

    50 square feet x 80F x U0.077= 308 BTU/hr

    Window losses:

    5 square feet x 80F x U0.6= 240 BTU/hr.

    OK, you're up to ~550 BTU/hr, so where's the the other (3200-550=) 2650 BTU/hr of the heat load coming from?

    When the room is actually occupied deduct 300 BTU/hr for one warm human sitting on the can, now you're at 250 BTU/hr.

    If you have a couple of 15 watt LED lights that's another 100 BTU/hr and it's 150 BTU/hr.

    Do you REALLY want to put 3200 BTU/hr of kick space heater in there?

    The only time it needs to be actively heated is when it's not occupied, or the window is open.

    Seriously, go with the UltraFin solution and keep the room up to temp (to avoid the lag-time issues). Even 20 square feet of radiant floor would be enough cover the likely load and it'll be nice and warm under bare feet and comfortable, even if the room isn't quite 70F.

    Making several tiny zones can create severe short-cycling issues for the boiler. If the bathroom is your only micro-zone it might still work with a high-mass boiler, since the total amount of heat emitted can probably not short-cycle, even with just the thermal mass of the boiler to work with, if it's cast-iron. What do have for a boiler? Any buffer tanks on the system?
     
  9. Thetruck454

    Thetruck454 New Member

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    Aparrently a bad online calculator haha.

    Boiler is an oil fired Vega B10/4. Currently the office, kitchen, and living room are one zone, bedroom and two baths are a second, and indirect hot water heater is a third. The house stays at 60 untill evening when we're home, then up to 70. At bed time even thing goes back to 60, cept the bedroom stays at 70. I was thinking the bathroom on it's own because I would only turn the heat up during weekday mornings to maybe 73 and maybe weekend too. If I left just that bathroom hot all day it wouldn't make sense would it?
     
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    WIth radiant floor heating, the response time is a lot slower than with radiators that are heating the air. It has to do with the difference in temperature...a radiator might have 180-degree water going into it for maybe the goal of 70-degree air. Radiant flooring at the surface is limited to maybe 80-90-degrees, so the difference that can heat the air above it is nowhere near the same delta. So, radiant takes longer to respond. A side benefit is that you can feel warm with a lower air temperature with radiant heat and the radiant floor heat is a lot more even verses a smaller surface area of say a toe kick or conventional radiator.
     
  11. Dana

    Dana In the trades

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    Is your B10-4 set up for oil, or is it gas?

    The Vega/Biasi B10 -4 has about 40lbs of water thermal mass and another 30 or so of water-equivalent cast iron thermal mass, for ~70lbs total. There may be another 10 lbs of water etc in the distribution & radiant plumbing to the bathroom micro-zone. Pulling 1200 BTU/hr (60 BTU/minute) out of it the temperature of that 80 lbs water-equivalent mass drops in temperature at about 60/80= 0.75F per minute. If the controls are set up for a 15F temperature swing (low limit to high limit) it'll take 15/.75= 20 minutes between firings when serving just that zone, or about 3 burns per hour max, delivering ~1200 BTU into the zone in that 20 minutes. The heat loss of the zone even at design condition is lower than that, so it'll really be fewer than 2 burns per hour on average.

    The burner rate of B10-4 puts 96,000 BTU/hr (1600 BTU/minute), so the burns will be dauntingly short (lesst han a minute) and inefficient when serving just that zone, but at 1-2 burns/hour that's not going to abuse the boiler or ruin the average efficiency. (If all zones were that small it would be an efficiency disaster!)

    The B10-4 would be ~2x oversized for most homes in NH, and if that's true here it won't hit it's nameplate AFUE. If it isn't currently fitted with a heat purging boiler control it probably should be retrofitted with one to cut down on standby loss, maximize burn times for a higher as-used AFUE.
     
  12. Thetruck454

    Thetruck454 New Member

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    Set up for oil with a Carlin ez-1 burner and non powereed direct vent. When you talk about purge, what do you mean? I know when a call for heat comes from the taco zone controller, the burner will run the fan for maybe 20 seconds before the oil control valve opens and it lights off. It does have a post purge where after oil is cut off the fan runs for I want to say 5 minutes, I don't remember which setting the dip switches were set at. As far as water temp, it's set up for a 30 deg swing, but here's where I'm not sure. The aquastat on the boiler output is set for 170-200. Yet when I watch the temperature gauge on the burner side that goes into the water jacket shows a range of 145-175, so not sure which is accurate.

    Part of the reason the previous owner may have gone so big with the boiler is the 24x24 garage was heated with a forced hot water modine. When I rebuilt the garage into a 30x40 I took that out and use a 5kw electric heater for only those times I need it. Im surprised on a 1200sqft garage that little heater will bring temps up the the 50's with it being zero out.

    What if I were to tie the bedroom zone on the controller to both the bedroom and bathroom zone valve to increase the load, yet if the bathroom calls for heat, say to heat up more in the mornings, it could then come up on it's own. During that time the bathroom temp goes up, the indirect water heater will probably also be calling for heat to increase the load. Or maybe I'm overthinking this...

    In regards to the ultra fin, how far from the toilet should i stay with tile floor and where does the response time fit between baseboard and traditional in floor radiant heat?
     
  13. Dana

    Dana In the trades

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    A heat purging boiler control on a new call for heat will not fire the boiler until the boiler's temperature drops to the programmed low-limit temperature. Some "learn" the system, and figure out how to turn off the burner prior to the end of call for heat to finish off the call for heat by purging heat from the boiler, parking it a lower temperature between burns (for lower standby loss) . By maximizing the minimum to maximum temperature swings it also utilizes the thermal mass of the system to ensure longer more efficient burns.

    With an oil burner a low-limit of 140F is fine, and if it can be set up for a 30F or higher differential swing the number of burns will be cut in half, and the burn times will be at least doubled from my prior napkin-math example using just 15F swing.

    Part of the inefficiency of very short burns is the flue purge prior to firing. The 20 seconds of fan prior to firing is taking heat out of the boiler. It's not much heat in absolute terms, but if it's 20 seconds of flue purge and 45 seconds of burner on-time, between the several seconds it takes for the burner to get near it's steady state efficiency and the flue purge losses it adds up to a double-digit percentage of the total heat imparted by the burn. Don't sweat it if it's just one zone doing that a dozen times a day. As long as the average burn times (all zones) are more than 5 minutes the total efficiency hit is low. If it's doing a dozen 1-2 minute burns per hour rather than per day it's taking a serious hit in efficiency and putting a lot of wear & tear on the boiler, which is something needs to be done about it.

    Give the toilet about foot of clearance from the heated part of the joist bays, and block off the joist bays to prevent convection from the actively heated part to the part under the toilet.

    Increasing the size of the zone doesn't help until/unless the combined radiation can emit a large fraction of the 96,000 BTU/hr of burner output. Is there 40-50' of baseboard in the baseboard in the bedroom ? (I'm thinking probably not.) Ideally all of the other zones would have more than 40' of baseboard (per zone) to minimize cycling of the boiler and increase burn times.

    If your putting 2 gpm of 105F water through the bathroom shower or filling a tub with 110F water, the water heater is heating the bathroom (even though a large fraction of the heat from the shower is going down the drain.)

    Don't use temperature setbacks with radiant floors- the response time is just way to slow for that to work as a strategy.

    If you're curious about your oversizing factor, run a fuel-use heat load calculation (using wintertime only fill-ups, to minimize the error from hot water use and solar gains, etc.) You're probably not going to be replacing the boiler any time soon, but having firm stakes in the ground bracketing where the true heat load is allows you to avoid oversizing errors in the future. In the unlikely event that your oversize factor is really only 1.2x a retrofit heat purge controller isn't going to buy you much. If the boiler is 3x or more oversized for the 99% heat load heat purge controls can buy quite a bit- often in the ~10-15% range for annual fuel savings- even more if the boiler has been short cycling a lot and the heat purge control cuts the number of burn cycles in half.
     
  14. Thetruck454

    Thetruck454 New Member

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    So if I used ultra fin for the bathroom, it would be the only part of the house that doesn't have a setback, how would that work? I'd think the bathrooms would constantly be losing heat to the rest of the house which would cause the zone to call for heat repeatedly and cause even more short cycling? Or is that thinking wrong?

    Also I'm boxing in part of the bedroom to make a walk-in closet. IIwas trying to figure a way to heat it with having no wall space and installing ultra fin in line with the bedroom baseboard may be the solution.
     
  15. Dana

    Dana In the trades

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    A 2x4 partition wall between rooms with half-inch wallboard on each side is about U0.25. A hollow core door is about the same. So if it's 60F in the rest of the house and 70F in the bathroom, assuming 175 square feet of partition wall + door and a temperature difference of 10F you're looking at:

    175' x 10F x U0.25= 480 BTU/hr of heat loss from the bathroom to the rest of the house

    Add that to up to 550 BTU/hr losses on the insulated exterior wall (only that high when it's -10F outside) and you're at ~1000 BTU/hr, when nobody is home, and it's -10F outside. So the worst-case really is the 1200 BTU/hr I used in the short-cycling example. Most of the time the heat loss of the room will be a LOT less than 1000 BTU/hr room loss, so an Ultra-Fin zone sized to emit 1200 BTU/hr won't actually be emitting that much continuously- there will be extended pauses when the thermostat is satisfied.

    When it's actually -10F outside the other zones will be intermittently calling for heat to keep the place at 60F, and there will be overlapping calls when both the bathroom & other zones are active, reducing the number of short-cycles, which only occur when it's just the bathroom zone calling. When it's 50F outside with essentially no calls for heat from the other zones, the total heat loss from the bathroom to both outdoors +house will be no more than 600 BTU/hr, which means longer periods between the calls for heat, and fewer short-cycle burns to keep it at temp.

    The heat loss of a walk in closet is extremely low unless it also has windows. Run the simple IBR napkin-math load calc I used in the bathroom example to ballpark it.

    In your original post you stated "The boiler outputs 150F-180F water..." . Does that mean the low-limit is set to 150F, with a high limit of 180F? If yes, that's twice the temperature swing I used in the short-cycling example, cutting the burns per hour in half- a burn every 45 minutes or so instead of 20 minutes or so.

    At 150F Ultra-Fin in 16" o.c. joist spacing with the fin pairs space 2' on center puts out about 25 BTU per square foot, at 180F it puts out about 40 BTU/hr per foot at 180F. So with 40 square feet of radiant floor it'll deliver output of 1000 BTU/hr or so at the cool end of the swing, 1600 BTU/hr at the 180F high limit. That takes about 13-14 fin-pairs. (square feet of floor divided by 3). If you don't have that much floor to work with tighting it to 15" on center spacing it'll put out a bit more, if need be, but it won't be quite the same BTUs per pair. They're sold in boxes of 100s (50 pairs), so you really aren't going to run out. Putting them under the tub or shower area will be about the same as putting them under floors. Putting the under cabinets would deliver may half what it does under floors. If you fit the insulation underneath but don't install the ceiling gypsum in the basement until later you'd be able to play around with it a bit to find what works, but it's unlikely you'll need more than something between 10-15 pairs to keep the place warm 100% of the time. Fewer fins mean a lower emittance, and a longer draw-down period on the boiler's thermal mass, fewer short-cycles, but it also means less heat. You might be able to do it with just 6-8 pairs and 25-30 square feet of floor, since the 1600 BTU/hr baseboard is probably overkill.

    Pore over the details in the manual before committing, but it's really a forgiving and fairly cheap system. A 100' of half-inch oxygen barrier PEX is less than $50 even at box stores, and a box of 100 Ultra-Fins is under $150, sixty square feet bags of R15 rockwool or fiberglass is less than $25, about the same price as 40 square feet of R21-R23 rock wool or fiberglass (if the basement is truly cold). So all-in you're looking at maybe $300, even with the ceiling gypsum sealing it all in as an air-barrier. Use only high density batts, otherwise the air leakage will interfere with performance. Don't be tempted to use crummy R19 instead of R21 fiberglass or R23 rock wool, or R13s instead of R15s.

    Insulate the entire floor, not just under the Ultra-Fin, and be sure to make some sort of air barriers in the joists to prevent convective losses to the basement through the joist bays with the Ultra-Fin. Where there is no tubing or fins snug the batts right up to the subfloor.
     
  16. Thetruck454

    Thetruck454 New Member

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    My heating pipes are 3/4". All I can find is ultrafin for 1/2" pex, how much of an issue will that be with all the other zones being 3/4?
     
  17. Dana

    Dana In the trades

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    If you break the half-inch PEX into two equal lengths to manifolds connecting to the 3/4" pipes on both the incoming and outgoing end it will have about the same pumping head as one 3/4"pipe the length of one of the halves. It it's only 40-50' of PEX splitting it might not be necessary unless the length of 3/4" plumbing on the zone is really quite long. Most systems are over-pumped in the first place, and the difference in heat output between 1 gpm flow & 4 gpm flow isn't likely to make it or break it. Roughly how much 3/4" plumbing (including the lengths of baseboard) are we talking on that zone?
     
  18. Thetruck454

    Thetruck454 New Member

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    The ultrafin will be the only thing on that zone and I'd be running 3/4 copper up to where I change to the 1/2 pex just before the ultrafin. Then back to 3/4 copper after the ultra fin. Total copper length is probably 20' to and 20' from the boiler.
     
    Last edited: Apr 26, 2018
  19. Dana

    Dana In the trades

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    You don't have to worry about even 50' of half-inch PEX then, and could even use half-inch for the copper runs to the boiler. Have you estimated the total length of PEX that would even be possible to run in those joist bays yet?
     
  20. Thetruck454

    Thetruck454 New Member

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    5 bays at under 9' a bay then you have to acount for the turns, but you also don't go to the edges of the rooms so I bet 50' is close
     
  21. Dana

    Dana In the trades

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    Even if it turned out to be 100' of half inch, a handful of 90 degree ells and some other random stuff ((such as zone valves a and mod-con boiler, etc) adding another couple feet of head to it, a typical old-school circulation pump like a Taco 007 would push more than 2 gpm through it. Just about any pump will be able to deliver adequate flow through the zone plumbing described. If it turns out to be noisy due to excessive flow (probably won't be, but it might) you may even want to throttle it back a bit with a ball valve.
     
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