Thermal shock - boiler vs hot water heater for hydronic baseboard heat.

oddball72

Hello, new to this forum. In the process of building our retirement home. Home designed for old age (no steps, no tub, wheel chair/walker access throughout), energy efficient and easy to maintain/economical to build, a basic box with a smaller box on front for entrance, 2 bedrooms, 1.5 bath, total SQ'ft with entrace is 1204 sq'. Foundation is a "Frost Protected Shallow Foundation" basically its a concrete floating slab with 2" of foam under it and the exterior perimeter is also insulated with 2" foam running vertically and horizontally away from the slab. 2"x6" exterior stud walls, with 1/2" OSB sheathing on exterior (will be insulated with R19 fiberglass PLUS 1.5" of rigid foam board on exterior over the OSB). Pella Encompass energy efficient vinyl windows. Special order energy heal trusses which will allow 18" blown insulation, R60. EPA wood stove for supplement/emergency heat. Primary heat...either a Slant/Fin Victory VSPH 60 or a hot water heater in LP fuel that will circulate heated water to hydronic baseboard along the interior perimeter of home, 2 zones (1 zone for bedrooms/bathrooms, 1 zone for living room/kitchen/dining etc.) The question I have is: Since I will be utilizing the EPA woodstove in the winter to lessen the cost of LP, the water in the heat system will be cold most of the time (especially in the zone for Living room/kitchen/dining) except for when we would go on vacation or not burn wood on a certain day. The second zone that heats the bedrooms/bathroom etc. would cycle more than the first zone, leading the boiler's cast iron exchanger warm and then if first zone called for heat, the cold water would shock the cast iron exchanger?? This is why I might consider a hot water heater BECAUSE...the hot water heater has reserve capacity to absorb the thermal shock/water temp difference plus I could use an antifreeze solution. I did a heat loss calculation online at -15 temp (Southern Upper Peninsula of MI) and because the house is so well insulated...the calculator came to needing about 34,000 BTU/HR (I could have done the heat loss wrong but I think Im pretty close). Now that 34,000 BTU/HR is for WHOLE house heating not taking into fact that I will be using the woodstove. Now because of potential thermal shock to cast iron boiler etc. I was considering a closed system, using the boiler or hot water heater with "MF200 Axiom Pressure Pal Mini System Feeder" so that I can have the antifreeze solution in the water, as my code does not allow for an antifreeze solution WITH potable water fill. Anyone have any ideas on which would be best?? I will try and upload the floor plan so anyone can get a rough idea of the home. Thank you for any assistance.

Jamie Hall

No need at this point for a floor plan -- and the choice of heating device is simple. Use a boiler, designed for hot water heat, for the hot water heating. Use a water heater, designed for producing domestic hot water for your domestic hot water (you might consider using a tankless for that).

Don't even think about using a domestic hot water heater for your hot water/hydronic heating system. They aren't designed for that, their efficiency in that sort of work is poor, and they will live a short and miserable -- and expensive -- life.

If the system is properly designed, with a boiler matched to the loads, there will be no problem with thermal shock on the boiler. They're built for it.

EBEBRATT-Ed

I agree with @Jamie Hall

Use a propane cast iron boiler and a tank type LP water heater probably 30-40 gallon. This will provide the least maintenance and problems. Don't use a tankless wh too many problems and don't use an indirect wh because the boiler will not be operational when you are on the wood stove.

Use a common brand of equipment that parts are easily available like a Peerless or Weil Mclain boiler.

Being that tightly insulated you may want to consider an air exchange unit for fresh air. Also combustion air for the boiler and water heater

EBEBRATT-Ed

As far as thermal shock that is an easy fix. A three way mixing valve with the sensor on the boiler return set to 135 degrees will keep the return water to the boiler above the danger zone

oddball72

@Jamie Hall & @EBEBRATT-Ed : Thank you both for the information. So, basically, trying to keep the system as simple as possible etc. I would go with the Slant/Fin VSPH series as its a "sealed combustion" boiler. I also looked at some Peerless such as PSCII-03 but not easily found. Then instead of a gas hot water heater, I think I would like to go to electric 40 gallon because there is something politically happening with our propane delivery service and "Line5" possible shut down. Since the LP boiler will only have 2 zones, I tried to look up some "3 way mixing valve piping diagrams" and all I could find was for in floor radiant heat NOT hydronic baseboard...is it possible that because there will not be the same amount of water in the hydronic baseboard zones vs infloor radiant zones that boiler will suffer much shorter thermal shock on the return piping? because I will be using hydronic baseboard elements, those operate at a higher temperature so it helps eliminate condensation within the boiler correct? I did download and read the Slant/Fin instructions and they state "Radiant Floor, Low Water Temperature and large water volume systems: A boiler by-pass loop, three way valve arrangement, or primary secondary pumping (with a boiler loop) must be used to provide a minumum 130˚ return water temperature to the boiler. This will prevent condensation on the cast-iron sections that can result in improper operation of the boiler." I know that radiant floor operates at a lower temperature so that is comfortable on the feet etc. but that does not apply here? If I don't need the mixing valve, it would make it a much simpler setup. Now, one other question for EBEBRATT-Ed - you stated that I might want to consider an "air exchange unit for fresh air" but will this be necessary in the following situation: I will be installing a fresh air kit on the EPA woodstove, Im sure this will leak some and provide air into the home, if the boiler is sealed combustion, water heater is electric, clothes dryer is electric also, would I need this air exchange unit? is there an alternative to it (something short of just cracking a window) because I looked at most installation instructions and for a single story home they don't show anything, they do for multi story or homes with basements in which intake and exhaust of the unit are separated by levels in the home requiring good size lengths of intake and exhaust piping etc. The only other air using appliance would be the bathroom exhaust fan and Im not sure how that will negatively affect the home. Again, thank you both and I look forward to more info from members such as you guys.

Jamie Hall

You can use a mixing valve with that boiler, if you need it. However, you may not. My concern is that if your heat loss figures are anywhere near right, that is too big a boiler, and that's never good. You could look at the Slant/Fin Sentry series, the smallest of which is in your range. However, I would also suggest you look at the Weil-McClain Ultra series, the UG-80, which, while it is bigger, is a modulating and condensing boiler which will run most of the time at a much higher efficiency than the Slant/Fin, and can modulate down to well within your heating requirements.

Much will depend on the quality of the installation.

On fresh air, the general consensus is that two to our air changes per hour are needed to maintain indoor air quality. This was not a problem in older houses, of course, but in newer ones it most certainly is. There are any number of good units available, and some can be installed satisfactorily in an unheated attic above a single story house with no basement. They do need some ductwork to ensure reasonably even distribution of the air.

Jon_blaney

Some thoughts:

Have you considered oil as fuel? Maybe LP is cheaper where you are but oil may be worth considering.

A gas or oil fired water heater can be used to heat a home but is used in conjunction with an air handler. I have been using such a system for 20 years with no problem. It is an open system which provides DHW and heat to part of my house. I think it works well with my woodstove. I think the reaction time would be better than you baseboard system. With all these systems water quality is important. Ductwork in a new building should be easy. Look up hydroair.

Go with two full baths. It will make staying in you home easier over the long term.

I would consider a boiler room attached to the outside of the house. Keeps all that dirty equipment out of the living area and provides easy access. It also may make venting easier.

Ctoilman

Central air is nearly automatic in new homes so I'd consider a hydro-air system.  A small 3 section cast iron oil boiler with an indirect hot water tank (assuming you want to fill a tub?) would be my choice.

ethicalpaul

I like the electrical water heater to avoid having to deal with another burner and combustion air source/exhaust hassles.

Be sure to check out the Rheem marathon with its rust-free plastic tank and good insulation.

Or if you really like to save money, try a Rheem "hybrid" (heat pump) water heater which in my limited but observant experience has been wonderful.

EBEBRATT-Ed

Electric water heater is not a bad choice for hot water with generally two people in the house. No burner or fuel and they last pretty well and are easily replaced.

I wouldn't use an indirect because your planning on burning wood part of the time.

I would use a simple Cast Iron boiler. I would use propane with your small heat loss and burning wood part time the smallest oil boiler would be way oversized and then you have the oil tank issue.

If you want air conditioning you can use an air handler with a cooling coil and a hot water coil (look at Majic Aire or First Company)

and that is another way to bring in some fresh air. Have an outside air duct tied into the air handler return and it will be automatically heated or cooled

EBEBRATT-Ed

Also look up "Caleffi 1" Thermomix" Mixing valve on Supply House.com. The brochure shows how to pipe it

oddball72

its wordy but here goes and thanks for all the great info from discussion contributors...

@Jon_blaney & @Ctoilman: I did consider oil as it supposedly burns hotter than propane, but maintenance etc. and minimum sizes for them just about rule them out for consideration. This retirement home has no bathtubs, main bath is "roll in - no threshold" shower stall with a bench designed in it, other bathroom is just a toilet and sink and all had to be wheelchair/walker accessible for old age. Wanted to keep the system as simple as possible, when a person ages, they don't want to keep messing around with maintenance etc., especially if I kick the bucket before my wife, she isn't going to want to monkey or pay for high maintenance. Can't go with 2 full baths as the house is already standing (when we poured the slab last OCT, I formed the shower pan into the slab), we pre-bought all the materials in March of last year BEFORE "epidemic" hit and lumber prices soared, even tho' the house was designed to be economical to build...I wouldn't even consider building it at today's lumber/osb prices. Design also has its own boiler/mechanical room in the center area of the house already, in that room will go the boiler/hot water heater/well pressure tank/water softner/electric panel, so it works out good.

@ethicalpaul: yes, I too like the idea of electric hot water, easy to maintain, my FIL still has his original electric hot water heater in his house he built....its 43 years old...just a electric water heater that is glass lined tank, he maintains it every year...the only problem he has is it only uses one element now as one failed and no parts available for it due to its age... IMPRESSIVE on his part to maintain it. So that might work out good for us as again we don't use a lot of hot water etc.

@EBEBRATT-Ed, I ruled out the indirect fired water heater...we had one in our other house we built and gave to our son...worked awesome but its a bigger house with 1 3/4 bath. That house we built 22 years ago and at the time Weil-Mclain had come out with their rubber o-ring cast iron boilers....a local HVAC had 12 boiler failures due to those O-rings...so we went with...a Utica SC4 (full cast iron boiler and cast iron push nipples between boiler sections, life time warranty on heat exchanger) and indirect fired water heater...Never had any serious issues until last year just before we moved out, we had 2 service companies come out...remember this is an old boiler, very simple to fix (at least I thought so), one guy said there was no "diagnostic" panel and he would have to get someone else to come look at why it wouldn't fire (never did come back), the other just took one look at the boiler and said it was too old to fix...quoted me $10k to replace it with a peerless boiler. So I ended up taking my time to learn everything I could about the boiler, discovered the gas valve had failed intermediately due to faulty wiring harness, fixed it myself for $350 and its working just like new. Now...things have changed a lot over the years...first no longer can get Utica boilers here and they don't make the SC4 anymore, I cannot buy any kind of boiler or major boiler parts here locally from plumbing supply stores without a license but I can from Menards or Homedepot (1 hr travel), so I'm stuck with what I can get online, most likely supplyhouse.com will be my purchasing place for this new setup. I saw the mixing valve and I like it and that will go into the system, and I still have preference for that Slant/Fin boiler...it seems a lot simpler than Burnham's ESC series with a "stepping gas valve" and "outdoor reset" sure that Burnham might be more energy efficient but how much will I actually save over the long run? all the programming features etc. and I still yearn for simplicity of the Slant/Fin. So before I decide on which boiler I'm actually going to use...I gotta ask you or anyone ( @Jamie Hall ) who can contribute...best online heat loss calculator as I think I better re-run my numbers again just to make sure. I'll have to tackle the fresh air intake as I learn more about them as that's completely new to me. Much appreciated everyone.

Jamie Hall

On the heat loss calculator -- I really like the one from Slant/Fin, here: https://www.slantfin.com/slantfin-heat-loss-calculator/

You can use it either on your smart phone, if you like, or if you scroll down to the bottom there is a place -- rather well hidden -- where you can click to use it on your personal computer. It's a little conservative in its values, I think, but not particularly so. It also calculates heat loss room by room -- and being sponsored by Slant/Fin, will make recommendations as to what products and how much of them you need, which you can ignore or use as you please.

One minor comment (and for your heat load I agree with your assessment of oil vs. gas) -- it's not so much that oil burns hotter; the actual combustion temperatures are not that different -- as it is that oil has half again as much energy available per gallon than LP. A detail sometimes overlooked in price comparisons -- but what it really means is that very roughly speaking you will get at much heat out of gallon of oil as out of a gallon and a half of LP.

Zman

Where is the concern about thermal shock with low mass baseboard and a cast iron boiler coming from?
Systems like the one you are proposing have been installed for 80 years with no issues. I don't think thermal shock is a concern. Aside from the exhaust fan, a simple cast iron boiler with baseboard heat is about as simple and low maintenance as it gets.

EBEBRATT-Ed

3 way valve is cheap protection for the boiler as it may get some cold starts

Zman

This thread has tons of great solutions. I sure hope these solutions find the problem they are desperately searching for.
The boiler is going to cold start, it is designed to. The few gallons of water in the baseboard loops are not going to make any substantial difference in the time it will take to get above condensing temp. The original question was thermal shock which absolutely won't happen in this situation.

aperson

Hello. I live in the northern part of lower MI. I decided as well to make my boiler my hobby after way too many HVAC company fiascos. I am glad you will be having a wood stove there is a primal beauty in heating with wood. I have a slant fin boiler, she is about 30 years and works great. I included pictures of her and my water heater set up. My water heater is a separate zone and heated by my boiler. I have a basement, main floor and small upstairs all on separate zones. I keep the basement at 53 degrees or 51 in the winter. I keep all floors at 51-53 degrees at night. I too also heat with wood. I have not had a problem with thermal shock. My boilers top operating temp is 180 degrees. If no zones are calling for heat the boiler temperature falls to room temp until a zone calls for heat then she works her way up to 180 but will stop when the set zone temp is reached regardless. The coldest water she(boiler) will get hit with will be 53 degrees because that is the lowest temperature of the floor zones. Also I don't know how my water heater pulls this off but she too does not constantly maintain level 4 hot water, the water heater kicks on at a lower temp.

oddball72

many thanks to all contributors. The only reason I asked about thermal shock is because of how welly insulated the house will be which will reflect on how long it holds the heat and how often the boiler will cycle which appears that it will only cycle mostly on the second zone (the bedrooms/bath) that does not get fully heated with the woodstove. Now all that's left is to double check my heat loss numbers to verify boiler sizing, haven't done it yet due to working on the house so much during the weekends. @aperson NICE setup, have a similar setup at my other house except for using a Utica boiler. Thanks again everyone for the education.

Hot_water_fan

@oddball72 Props to you on designing such an efficient forever home! It'll provide you years of comfort. I think one heating option that hasn't gotten it's due and fits your house well would be a cold climate heat pump (think Carrier, Mitsubishi, LG, or Fujistu).
First, you have a low heat loss due to your levels of insulation and floor size. Almost all LP or Oil boilers will be significantly oversized and prone to short cycling with a low mass system.
Second, on a fuel cost basis, propane and heating oil are extremely expensive in comparison, especially if you're considering a standard efficiency boiler. Using Michigan's average propane price of $2/gallon from the EIA and its average electricity price of $.14/kWh, and a boiler efficiency of 80% and a seasonal heat pump COP of 250%, the heat pump comes in 40% cheaper on a MMBtu basis (calculations attached). It could be even cheaper than wood, but those costs are more variable and individual. Plus wood can be fun. If you're expecting ~8900 Heating Degree Days (output of 90MMBtu/year or so), a heat pump would save about $1000/ year vs. propane.
Third, these cold climate heat pumps can heat well into the negative temperatures. Adding electric resistance heat gives you a 3rd level of redundancy (wood stove, heat pump and back-up electric). The electric resistance could be either integrated into the air handler or electric baseboards to give room by room control.
Fourth, you can buy down the price of electricity with solar, either now or in the future after further cost declines. It's likely that solar can already beat the average Michigan electricity price handily, which would pair well with your plan for an electric water heater. There are options to do this with no upfront cost.
Fifth, with a low load home, you'll find that the wood stove is prone to overheating the place if it's warmish outside. A heat pump can modulate down to a low output at the milder temperatures, better matching the load at high efficiency to boot. Using Newberry, MI as an UP example: 70% of daily average temperatures are greater than 30 degrees, which is a heat loss of ~15,000 Btu for your house. Can you find a stove that can comfortably output 5k Btu/h? 35% of all days will be cold enough to need heat but need less than this output.
Sixth, depending on your floor plan, you could use a small ducted unit which could be inconspicuously added to serve the two bed rooms and living area from a centralized location.
Last, a heat pump provides AC and dehumidification (may be desirable now or in the future) and can easily filter your indoor air. With a modulating fan, energy use is low and airflow is barely perceptible, allowing for 24/7 circulation/filtration at low cost.

Congrats again on the well designed house.

Ctoilman

Big problem with heat pumps is the equipment is maybe good for 10 yrs then expensive repairs crop up....negating any efficiency savings.  A more long term perspective should be considered.

Hot_water_fan

Saving $1000/year for ten years more than pays for a new one, and if it's 15 years, even better. Plus cooling/ cleaner indoor air.

Ctoilman

1gallon of oil (115,000 usable btu) for $2.35 compared to an equivalent $7.05 in electricity. And heat pumps in cold climates need backup heat (electric resistance elements).  Ouch.  And if you want an emergency generator to run home heat (remember the catastrophe in Texas?) a heat pump system will need an expensive large generator, whereas a fossil fuel system needs the equivalent power source for a microwave.  Something to think about.

Hot_water_fan

All these costs are in included in the $/MMBtu calculation above - your oil example ($2.35 x 1,000,000/115,000) = $20.43/MMBtu is 20% more expensive. The $7.05 you mention is at $7.05/(115,000/3412) = $.21/kwh, 50% above the Michigan average, plus solar could be an option to bring the rate lower. The 20% savings already includes electric backup heat, which will be used only sparingly with the cold climate heat pumps (Mitsubishi makes a heat pump that puts out ~30,000 Btu at -5). The OP is installing a wood stove as a backup heat source and can keep a small generator.

SuperTech

Hot_water_fan said:

Saving $1000/year for ten years more than pays for a new one, and if it's 15 years, even better. Plus cooling/ cleaner indoor air.

Cleaner indoor air? Have you ever seen the black fuzzy crap that accumulates on the blower wheels of these mini splits? Every one I see has it all over the wheels and the white plastic by the blower after one year, even in the cleanest homes. I wouldn't want to be breathing that air. 

Regarding the "smallest oil boiler will still be over sized", I haven't come across a single home that this problem couldn't be solved with a buffer tank or reverse indirect water heater. I'll take a proper hydronic heating system that will last reliably for decades over any mini split. A ducted A/C system will dehumidify much better and be easier to service.  

Ctoilman

And so what if the oil or gas boiler cycles some??!!  Do you really think that is going to dramatically influence fuel usage?  In 35 yrs in the biz, so to speak, an oversized unit, within reason, may use a bit more fuel but will offer the capability of home heat load expansion (pool heater?, addition?, etc) and not require a larger boiler down the road.  If ya wanna get fancy (complicated) then modulate boiler temp with outdoor reset.  Better yet, save fuel with better windows and insulation....now that's money in the bank.

Ctoilman

FYI: those HP's that advertise low temp performance put out barely warm room air temps when outside temps are frigid my customers don't like that all.....it feels like a draft coming from the unit.  Don't get me wrong HP's and mini-splits are pretty good in the shoulder seasons and summer, but where it gets really cold out they struggle.  Overall, not for me.

EBEBRATT-Ed

I used to do service and spent many a 0 degree day on a roof working on roof top units.Not fun

I don't see Heat Pumps as primary heat in a cold climate. The simple fact that they loose efficiency as the temperature drops is one reason.

I also wouldn't want to change a compressor on one when the temp is 0 degrees.

Maybe someone can tell me how to correctly evacuate a system at that temperature. It can't be done, any moisture that gets in will stay in the system. You can't pull a low enough vacuum at that temp to boil water

Hot_water_fan

@SuperTech Doesn't have to be a mini-split, a ducted heat pump would have similar fuel costs. I was talking about the ducted Mitsubishi above, the black fuzzy crap doesn't apply.
If OP is concerned about fuel cost (as stated), propane/oil are just hard to justify, plus propane/oil prices fluctuate while electricity prices are stable and you can decrease them with solar. Natural gas would be a different story cost-wise, but still provides no cooling. Adding a buffer tank/modulating boiler/ODR would of course help with cycling but then you quickly get to the point where a 30-year boiler's lifetime cost with no maintenance is significantly more than 3 heat pumps if you go with the pessimistic lifespan. I appreciate hydronic systems most, if only air-to-water heat pumps were more widely available we could have the best of both worlds. I agree with @Ctoilman, dumping more cellulose in the attic or being more choosy with the windows is the best investment.

Jamie Hall

Honestly, for new build construction there is no excuse not to go with very good insulation, controlled air changes (heat recovery ventilators) -- and 80 plus percent direct passive solar heating. My father in law (since deceased) and I were designing and building such houses (and a school dining hall, among other things) 60 years age (yes, early 60s). In New England.

Heat pumps do have a place, no question. That place is not retrofitting buildings which were designed for 140 plus hot water heat in winter conditions. Never mind higher temperature systems -- and certainly never mind steam.

A craftsman will use the right tool for the job, not attempt to make the latest whizzy thing work -- never mind his or her own pet concept. A good engineer will do likewise.

Politics may force us all to do things which are somewhere between impractical and insane, but in the meantime let's ate least try to do the best job we can for the client.

oddball72

Wow, intense discussion....@Hot_water_fan, I'd like to research more into alternatives, however...for my limited knowledge of heat pump systems, I can surely tell you that I have no way to install that and I refuse to work with any local heating/plumbing contractors because, in this epidemic, they got the buyers by the b@lls so to speak...our whole goal with this retirement home was, energy efficient and ECONOMICAL to build...all these other alternatives (Heat pumps, solar, etc.) are beyond the scope of my abilities and what I'm willing to pay to have the house built. When you reach a certain age, you just want a place to lay your head and be happy, not needing a fancy home, just someplace to prepare for your next journey, keeping things simple and easy to maintain without having to rely on so called professionals that just seem to see $$$ signs. I'll give you an example and these are real world...I had 3 estimates to do the DWV system, just the rough-in stub outs so I could get the slab poured, each plumber I contacted was over $ to put this in place...this was for $ worth of PVC, and each one had said good luck finding someone to come during this epidemic. I've done plumbing before, no expert here and not claiming to be, I did the whole DWV on my own and passed the first inspection and the inspector himself said I did a great job and I kept the costs down. Second, our plans originally called for in-floor radiant heat. Now this I've never done before and I researched and researched to all ends even contacting design firms etc. even received tubing layouts etc. and materials list for just the rough in...Was not comfortable trying to do this on my own, and again contacted heating contractors who quoted over $ just to lay the tubing and provide the manifolds, nothing else, to do the complete system with condensing hotwater boiler, $. I just couldn't do it, where I live you have to know how to do many things just to survive, so I did what I know how, hydronic baseboard, putting wrapped/insulated soft copper under exterior door ways and will run the hydronic baseboard as this is how my other house was done. This retirement house was assigned a complete budget price of $ (turn key) WITH well and septic and I will meet that mark, live with the results as best I can, we look at it like this - sure beats living in cardboard box.

I really appreciate all recommendations and if money was no object I would consider alternatives. So I will more than likely be going with a sealed combustion cast iron boiler with zone valves, highly reliable/easy maintenance and within my abilities. Then an electric water heater, electric clothes dryer, electric stove all to minimize dependence on LP but that then makes me reliant on electricity more and here in the U.P. you can lose electric for a few days and that's normal, so if that happened during the winter, the wood stove which requires no electricity, would keep the whole house from freezing up. For all the research I've done so far, again I think the HRV's are going to be my biggest issue...all of the ones I have seen are for bigger homes than what I have and their installation/duct balancing diagrams are for multi level, I have contacted a few companies asking to get in touch with their engineer's or tech support for a diagram for single story home, no one replies these days.....and I might have hit a road block on that for now.

Many many thanks to all contributors, each of you have given me much information and assistance, even if its something I'm not going to utilize, its still appreciated, random people read these comments/replies...and contributors ARE helping to educate many others and you all deserve a pat on the back and a cup of coffee (or even a beer n cheer ).