System Design - Hydroair plus Radiant

Dan_15

I've lived in an old house for a long time and dont know much about modern systems that would go into new construction--looking to get a reality check and a bit of education about the considerations for new systems. 



We are renovating an old house down to the frame--it will be a tight envelope with new windows, doors, icynene, etc.  There will be 3 floors plus finished basement, approx 4000+ sf when all said and done with various additions.  Our HVAC contractor proposed hydroair mainly because he says its a small incremental cost to add coils onto the AC ductwork that will be installed anyway.  I've always lived in a house with radiators, so I am a bit skeptical of hydro-air.  After discussing some more about comfort and efficiency, he thinks we can do radiant loops for the entire main level, which will be an open floor plan design, and that the 1st floor will act as a giant efficient radiator and the heat will rise to 2nd and 3rd floors.  He thinks hydroair will work sufficiently to supplement as needed on those levels.  He thinks panel radiators would be overkill on 2nd and 3rd levels.  we would also do radiant in basement since we are replacing the slab, and cost would be about the same as baseboard in that scenario.  For the radiant system, he proposed loops hung in aluminum "tracks" between joists (not sure if he meant extruded plates) with foil backed insulation and a small air gap.  We did not discuss loop length or size of PEX.



He proposed a W/M Ultra to supply the heat.  He thinks ODR will be well-matched with radiant on 1st level, but not so much with hydroair because temps will be higher and variable speed fan will do a lot of modulating based on call for heat.  I asked him to do a formal heat loss calc and he said certainly will do that, but not as worried about being too exact because modulating boiler will adjust itself accordingly.



He proposed running the vent through the roof to keep the appearance of condensation out of the way, and he did seem very sensitive to making sure there is nice neat piping with lots of shutoffs for service.



Does this sound reasonable or not....I'm sure I am not stating the design 100% accurately...are there any red flags with such a hybrid design that I should be asking about?

Thanks, Dan

Steamhead

Does the house

have radiators now? If so, keep them. They will out-perform any duct system.



The only advantage of hydro-air over the usual furnasty is that if the heat exchanger cracks, you get a water leak rather than a carbon monoxide leak. You still have all the other drawbacks of a duct system- accumulation of mold and other nasties, moving air makes you feel cold in the winter, pressurizing/depressurizing the house, air leaks from bad duct joints. From a comfort and efficiency standpoint, ductwork is the worst possible way to go.



If it's a choice between hydro-air and new panel radiators to add to the radiant, go with the panels.



The heat emitters must be sized to the heat loss of the spaces they're in. That's why we do the heat-loss calculation- to size the emitters as well as the boiler. Don't depend on the first-floor radiant to heat the entire house.



Don't know why that contractor is pushing hydro-air- maybe he really doesn't want to do hydronics. Maybe it's time to switch contractors.

Jean-David Beyer

I am not a heating professional.

"He proposed a W/M Ultra to supply the heat.  He thinks ODR will be

well-matched with radiant on 1st level, ... .  I asked him to do a formal heat

loss calc and he said certainly will do that, but not as worried about

being too exact because modulating boiler will adjust itself

accordingly."



I wonder if this is a problem with all W/M contractors. I have a W/M Ultra 3. My contractor did not do a formal heat loss; he paced around the outside of the house to estimate floor area, and guessed his way from there. I did not care for that, so I did a heat loss myself. Three ways. My old (oil) boiler took 70,000 BTU/hr input and always provided enough heat. So that was an upper bound on what I needed. I also did W/M's heat loss calculation:



http://www.weil-mclain.com/en/multimedia-library/pdf/weil-mclain-pdf/other-downloads/boiler_replacement_guide.pdf



This seemed oversimplified compared with the procedure in John Siegenthaler's book:



http://www.heatinghelp.com/products/Books/5/96/Modern-Hydronic-Heating-Second-Edition-br-by-John-Siegenthaler



I also used the Slant/Fin program.



I have never been sure if the results represent the heat input to the boiler, or the heat output. My guess is that these can be off so much that unless you have an awful boiler, it will not make much difference. Not because a 20% error is insignificant, but because the GIGO principle says if I make 20% errors in the inputs (infiltration losses, effectiveness of windows, solar inputs, effectiveness of insulation in the walls, ...), I should not expect much better as the outputs of the calculations.



These last two indicated I really needed between 30,000 BTU/hr and 40,000 BTU/hr on the design day (I have a small Cape Cod house in New Jersey). In spite of this, he suggested the WM Ultra 3 105,000 BTU/hr just to be safe, and not to worry, because it would modulate down to 21,000 BTU/hr. This did not make sense to me, because it seemed to me that it would always be running at the low end, so I would not be getting any modulation to speak of. So I insisted on the 80,000 BTU/hr one (their smallest) that goes down to 16,000 BTU/hr. (all these are input to the boiler). And having run it for a winter now, I wish they made a 50,000 BTU/hr model that would go down to 10,000 BTU/hr as my upstairs heating zone needs little heat and cycles on and off except on the coldest days. (Not as fast as the old oil boiler did, but still more often than I would like.)



So do not let him fool you into taking too large a mod|con boiler for your needs.

Dan_15

System Design - Hydroair plus Radiant

Thanks for all your thoughts.  So....the house currently has standing cast iron rads throughout (which I know are great).  I guess my only beef with them--and maybe this is not completely legitimate--is how they will look in a modernized space, as well as the loss of floor and wall space.  I'm also concerned that repiping would be very painful if I ever decided to replace them with something like panel radiators, especially with supply and return on the same side of the panel.



You're right, I dont want to rely on a guess about heat loss to the 2nd and 3rd floors. My main take away here is to get a real heat loss done, and size the boiler and emitters properly--whether they be panels, rads or ducts.  Proper sizing and install is more important than whether to choose WM Ultra versus Lochinvar. 

Thanks again, Dan

Steamhead

Keep the radiators then

That's one less thing you'll have to buy. If cleaned up they'll look great, and you can't beat the comfort (and therefore the efficiency) they will provide.



Why replace something that works well?



Ask your contractor that and see what his answer is.

CMadatMe

System Design

I would get a second opinion on this. The thought process that the radiant 1st floors heat would rise is off base. There is very litttle to no convection in radiant and we are not heating the air but controlling the heat loss of the objects in the room to include humans. So you will not get the rise your being told.



The first mistake that is made when combining hydro air and radiant is the non use of set point controls/floor sensors. The use of sensors allows you to maintain some type of floor temp so you maintain floor warmth and limits dead bang cold floors or the radiant having to come up from dead cold.



 As for panel rads. They work great in conjunction with radiant. You can use a radiant manifold for them and if sized correctly can run the same water temps and the same 3/8" pex tubing you are using for the radiant. I would like to know what the definition of overkill is. I never thought the comfort and efficiency I recevied from my heating system was overkill. It's just the opposite.

 For your joist heating if you are using good plates there is no need for air gaps between the plate and the insulation so as long as you are using an insulation with a valuve of R-19 you should be good to go.



Again you may want a second opinion or do yourself a favor and do a little more research on what system you want. Best of Luck

bob eck

heating system

take a look at using triangle tube prestige solo boiler 95% AFUE boiler.

first floor radiant sounds great. look at installing cast iron radiators or aluminum radiators.

size the radiators to run on 120*F low water temp coldest day/night. the lower the water temp you send to radiant and radiators the lower your energy costs will be. triangle tube prestige solo does not require high head circulators this boiler also comes with outdoor reset control use their smart stainless steel indirect water heater for domestic hot water. can get 5 or 10 year parts and labor warranty on this boiler thru a professional heating contractor. spend a little more money on the original design and install to make the heating system as efficient as you can because the cost of energy is always going up.

bob eck

heating system

take a look at using triangle tube prestige solo boiler 95% AFUE boiler.

first floor radiant sounds great. look at installing cast iron radiators or aluminum radiators.

size the radiators to run on 120*F low water temp coldest day/night. the lower the water temp you send to radiant and radiators the lower your energy costs will be. triangle tube prestige solo does not require high head circulators this boiler also comes with outdoor reset control use their smart stainless steel indirect water heater for domestic hot water. can get 5 or 10 year parts and labor warranty on this boiler thru a professional heating contractor. spend a little more money on the original design and install to make the heating system as efficient as you can because the cost of energy is always going up.

bob eck

heating system

take a look at using triangle tube prestige solo boiler 95% AFUE boiler.

first floor radiant sounds great. look at installing cast iron radiators or aluminum radiators.

size the radiators to run on 120*F low water temp coldest day/night. the lower the water temp you send to radiant and radiators the lower your energy costs will be. triangle tube prestige solo does not require high head circulators this boiler also comes with outdoor reset control use their smart stainless steel indirect water heater for domestic hot water. can get 5 or 10 year parts and labor warranty on this boiler thru a professional heating contractor. spend a little more money on the original design and install to make the heating system as efficient as you can because the cost of energy is always going up.

bob eck

heating system

take a look at using triangle tube prestige solo boiler 95% AFUE boiler.

first floor radiant sounds great. look at installing cast iron radiators or aluminum radiators.

size the radiators to run on 120*F low water temp coldest day/night. the lower the water temp you send to radiant and radiators the lower your energy costs will be. triangle tube prestige solo does not require high head circulators this boiler also comes with outdoor reset control use their smart stainless steel indirect water heater for domestic hot water. can get 5 or 10 year parts and labor warranty on this boiler thru a professional heating contractor. spend a little more money on the original design and install to make the heating system as efficient as you can because the cost of energy is always going up.

HDE_2

More than that

Hydro air offers more advantages than that

Besides ducts for AC, you can have simple yet whole-house humidification, air cleaning, UV and so on

IMO a great heating system involves both radiant and a smaller amount of supplemental Hydro air with a ECM blower.

hydrohead

The Best

A proper heat gain/loss is a must.A properly designed and installed duct system with a steam injection humidifier and whole house air purifier using an ecm blower as part of a complete hydro air system can not be beat...warming the floors is nice too.size the radiant for floor warming only.heat with hydro

Dan_15

Second Opinion

Thanks again for all the comments.  We will certainly plan to get another opinion, from someone more familiar with radiant, and of course, do a proper heat loss calculation for sizing the boiler and emitters.  I am still skeptical of hydro-air and have the impression that keeping the CI radiators on 2nd and 3rd levels will go nicely with ODR and lower temps, which is an agreeable scenario for pairing with radiant on the 1st level. 



I have also heard mixed reviews of W/M Ultra, and will look into other boilers such as Lochinvar, Buderus GB and TT Prestige.  Viessman may be a bit out of price range.  I am a fan of sophisticated and integrated control strategy and would prefer something highly customizable.  I love the controls on my Buderus G215 boiler in our current house.  Any opinions about the choice of boiler for this kind of application would be much appreciated!

Dan

CMadatMe

I second that thought

Go with the rads. The Viessmann is priced competatively with the other mod/cons and you can really tune in the 2 heating curves very easily.

Jean-David Beyer

heard mixed reviews of W/M Ultra

I have a W/M Ultra 3 (80K BTU/hr in put model). But I have had it only a year and it worked just fine this winter. I read a lot of reviews about it, and they seem to be of three types.



1.) Some were installed by people who did not know what they were doing, and they got bad results. But this could happen with any badly installed boiler, I guess.



2.) The early production of the Ultra 3 models had a problem with the U-control control board. The problem turned out to be that there was no pre-pump interval, and this could result in the boiler shutting down because the return water was much hotter than what was in the boiler, and gave a temperature rising too fast diagnostic message. This is the interval they run the circulator before letting the boiler fire. Later production came with a new control board (that I have) that has has a pre-pump interval that is set to 20 seconds by default (and I have left it there). I had no problems with it that way. It can be adjusted from 0 to 240 seconds.



3.) Concern about life-time of the aluminum heat exchanger. I think this is the most serious issue. I do not know if the votes are all in on this. Some argue that aluminum has greater heat conductivity than stainless steel. While that is true, it has to be thicker and my guess is that, on balance, the greater thickness will balance out the higher conductivity. So how long will it last? Presumably, if designed right, it should not burn out from the fire on one side and the water on the other, though I suppose it could. The thing I worry about is the steel and copper pipe and cast iron circulators, flow check valves, etc., and the aluminum heat exchanger. W/M are explicit about the water chemistry, and mine seems to be within the limits they specify (pH between 7.0 and 8.5), hardness less than 7 grains, and chlorine concentration less than 200 ppm. I may know more next week when my first service is done and they are supposed to disassemble the heat exchanger and in spect the fire side and clean it if necessary.