I posted here once previously (below), as my new modular and tightly sealed home (1100 sq ft) with a new Bosch 151 single zone FHW into +/- 30' of copper baseboard that seems to either misconfigured, misplumbed, or otherwise wrong. My two 120g LP tanks were filled on 11/22/17 and today (12/28/17), they are below 20%. The LP is used exclusively for the combi.
I am concerned that this seems to be fairly high usage for such an energy efficient system, in a well-insulated and air-tight home. It directs my attention again to my combi, and whether it was put in properly.
I am wondering what the experts think is normal LP usage for this system in an average modular very tight and insulated home with average temperature of 22.4-degrees F (Avg low of 13.3). Does ~150gal of propane for 30 days seem right?
My builder and the executor of any warranty service says it's normal, and that I am more likely to bother the HVAC installer than find a problem, but, as the below post details, something doesn't seem quite right. I still can't seem to alter room temperature unless the kitchen kick space heater is on.
Do some HVAC companies do quick visual inspections to help a homeowner determine if there is a plumbing or sizing problem?
Thank you for any insight you can lend.
https://forum.heatinghelp.com/discussion/163363/pri-sec-pump-mismatch-or-gravity-back-flow-homeowner-needs-help-long?
Comments
Once you have that, you can compare that to the amount of gas used -- which is somewhere, in your case, around 20,000 btu per hour. Comparing that to the expected heat loss will give you a pretty decent estimate of overall system efficiency.
(Considering today -- it's -4 where I am -- I wish I could come even close to that -- I'm running through close to 150,000 BTU per hour!)(of course, I have about 7 times the floor area, too).
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
30 feet of baseboard will only give you less than 20,000BTU/hour.
To me this could be kind of light for 1000 sq feet but like I said, no guessing do the heat loss.
You may be short of baseboard
How many BTUs does a Bosh 151 do??
If that is a 150,000 input, at full fire it consumes over 1-1/2 gallon per hour. A gallon of lp at around 90,000BTU.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
I agree about the lack of BB. 30' is gonna give you 15k btus output with 170* AVERAGE water temp. But why in the world would you want to run a mod/con at high temp like that? You're loosing all sorts of efficiency and defeating the purpose of the mod/con.
You're also experiencing the flaw of most combi boilers: in order to produce enough domestic hot water, they have to be grossly over-sized for space heating. The boiler is 151k btus and you only have enough BB to emitt 15K!
You can choose to do what you want, but you cannot choose the consequences.
For perspective my heatloss for 3,200 feet at -40f is 40,000 btu.
The clues are in that outdoor reset, or supply temp sensor were not even installed.
Put a HE boiler in get the rebate done. Such a waste of equipments possible potential.
However with a combi you will suffer from over sizing on the CH side to get the output for DHW, but there are some combis out there with higher tdrs to combat this scenario.
Your builder, and installer are praying on your lack of knowledge. Your getting a 90 plus boiler that may never see mid 80's efficiency until some changes are made. More emitter, implement odr. Get the return temps to the boiler below 130 to condense, and pickup efficiency points.
I would also bet that 30% or more of all outdoor reset systems have either been not installed, disconnected or adjusted to always shoot for a much high temp than needed.
Oversizing LP units affects the fuel bill more than oil or natural gas.
You are right, most combi's are way oversized for heating and should be limited to the proper applications. The only way in most cases the combi has any chance of working properly in both applications is if it is a 10:1 turndown.
If you size a combi for heating the house there is usually a higher hot water demand than combi's can supply.
I think you need about 3 times the baseboard that you have, and your boiler needs to be able to cycle down to less than 15,000 btu's to even begin to do a decent job of heating your new house,
you're leaking fuel
Your LP company is ripping you off
Another appliance or appliances is/are gobbling fuel
your combustion is poor and that needs to be addressed pronto
Your burning cleanly but the boiler is puttering away cycling like a dog, wasting energy
Your circulation is poor, can't move the energy.
Your heat emitter system is needing some luv, poor heat transfer.
your home is leaking heat at an abundant rate, any icicles?? Attic access open? Your snow looking good on the roof? better or worse than the neighbors?
or, last but not least, a combination of the above
Normally speaking, fuel burned equals heat generated.
Edited....I have heard that LP company theft exists, probably does and probably the nasty 1% of our society
Wilson Services, Inc
Northampton, MA
www.wilsonph.com
[email protected]
" I still can't seem to alter room temperature unless the kitchen kick space heater is on"
That's my clue that he is short on baseboard for his heat load.
Yes, their are other issues maybe the wrong boiler and maybe on set up properly etc.
1 gallon of propane has 91333 btus
150 gallons in 30 days. However I don't trust % gauges on propane tanks as accurate measurement.
That's 13,699,950 btus for 30 days
456,655 btus per day avg.
19,027 btus per hour avg.
.21 gallons an hour avg. consumption. 4.99 gallons a day.
Hot water is not accounted for.
Sorry one must consider the whole system not just the boiler. No a btu made is not necessarily going to what it's made for. Out the vent.
I am hoping to be able to come to them with some hard facts, and this thread gave me very much info to help me with that. I think the roughly 15k max of 30' of baseboard, and the min load on the combi of 46.4k means it is always cycling.
I also mentioned the lack of the ODR or the factory-recommended and included room thermostat to the HVAC contractor, who said "your system is too small to need that ODR, and the Bosch Comfort Sensor is for a different type of system." He gave no explanation for these opinions, however.
A complicating factor is that these modular homes are usually built for a buyer to spec, and this one was built to sell. Many of the features and decisions that are usually made by the home-buyer were either made by a random uninvolved contractor, or not at all. I don't know if the HVAC contractor considers me the customer, or the builder. I certainly don't feel served, but I won't give up.
One last question raised by a comment here: Should I be trying to run lower FHW temps for the condensing boiler? I saw a reply that said to shoot for return temps around 130F. Is a rule of thumb that I should run the lowest FHW temp possible to heat the space?
Thank you again, and I will check back in when I have my calc figures. I am hoping to find that adding a certain number of BB feet will help.
From what hvac contractor has told you solidifies my assumptions as he is incompetent. I would ask for his card so you can “not”recommend their services to others......
Because your probably short on baseboard you can't lower the water temperature...you won't get enough heat. Basboard output changes with water temp the higher the temp the more heat you get but boiler efficiency goes down
The boiler is another issue, if the lowest your boiler can produce is ~45k, that is always going to be a problem with a house that has a design heat loss of ~20k, or less.
If re-doing the baseboard is possible, this is the option I'd recommend you pursue. Install as much as you can. Use a high output baseboard.. Offer to pay the cost of materials. Do the room by room heat loss calc and post it, we can help you size the radiation.
System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
Your "tightly sealed 1100 sq ft home" could realistically have only 11K BTU's heatloss on the coldest days of the year, and considerably less on less than frigid days.
30 ft of baseboard (assuming 170F Average Water Temp) is probably sufficient.
A mod-con with a minimum output of 36K BTU's is outrageously oversized for this application and will be a short cycling disaster with a short life.
With such low heatloss, there's literally no Mod-Con boiler (running at efficient return temps in condensing range) that won't short cycle on all but the coldest days.
To "do it right" you probably need to almost double your radiation, and replace the boiler with a 10:1 high turndown small mod-con like the HTP UFT-80W which has a minimum output of 8K BTU's.
Just to keep things in perspective.... a modern gas stove top burner puts out 8K BTU's.....
I ordered two 70,000 BTU boilers and it took over a week to get them. "Oh, would never sell a 70,000 BTU boiler, we have the 110,000 and the 155,000 here though, are you sure 70,000 is big enough?"
Yeah.......
But now I live with 3 of them
I also have a Lochinvar Cadet in the shop and a Nobel in my home. Properly applied they work great. Only the Cadet in my home is close to the correct size for heating at design, still I included a small buffer.
In the shop I have a portion of the 500 gallon wood buffer connect to the Cadet, so it never short cycles with a 30K design load.
The nicer combi models have ramp delay and electronic limiting to tame the heating side down to 20% of max fire. The max fire of course for DHW.
So they are appropriate in many applications where small space dictates a single unit, or the loads match, or you buffer and limit their firing.
The combis are opening some interesting hydronic markets for small, tight space applications.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
I bet that a manufacturer would not sell many though, I hope I'm wrong about that though.
The ceavate is in low load homes you may only need just above set point water temps. So the love of warm floors goes away. Then it becomes when does radiant make sense.Neutral should be the goal no matter what anyway.
I think radiant ceilings in a low load structure reaps the rewards of cheaper panel assemblies, and not having to grief about not having the floors warm, floor covering hassles,cabinetry, and furniture. Ceilings gives the abilities of higher tube densities than floors to keep those water temps low.
I have two questions:
- High-output emitters; can you point me in a direction to research those? Of course I will google it in the meantime.
- Do you think the possible design flaws in the plumbing of the Pri/Sec loop (>4" separation) can be affecting this as well?
I am new to the Pri/Sec concept, and at first, I just couldn't wrap my head around the idea of not having the flow always directly through the exchanger. Now I think I understand that concept, but am not sure it has been implemented in a way that serves the primary purpose of sending hot water out to my baseboards and getting cooler water back to the boiler to heat. I will take new measurements since my lowered pump settings (described in my original post, linked in this post), but it still seems that radiators alone should be able to heat the space, without a kick-space heater running at full bore, and that my return temperature shouldn't be so drastically different. Also of concern is that, if the p/s loop is poorly plumbed, could it be pulling it's own hot ware back into the return side instead of sending it out to the baseboards?The following is not important, and just my rant/vent/opinion/wishes/dreams:
I really wish I could just say, "Something's wrong here," and the builder and HVAC folks would do their magic and help.
I'll stay optimistic and wait for my heat-loss figures. Perhaps my home really does only need 10 to 15k BTU. Yesterday was -25 in the AM, and climbed up to 9 by 3pm. This morning, it was -10. The house did not drop temperature overnight, so it can maintain temp, but the need to have the kick-space heater fan on high makes watching TV difficult, not to mention it seems like it is supposed to be an accessory, not a required component.
I have seldom-used rooms with doors closed and baseboard vents closed completely to help get more heat into the main spaces. I think the last time I looked at the Combi special functions, I saw that it is always running at 30% on the FHW side. I would guess that is its lowest possible modulation. I don't know if my flow rates are right, if I have enough baseboard, or if the plumbing was done properly. I only know that I have filled our tanks three times now, and we expected to be using roughly half the energy we have used so far, for the entire year, based on our research and the claims of the builder. January 2 and we've already spent $1,350 on propane.
Oh, one last question: When we moved in, we were horrified to discover that this combi can't modulate low enough for DHW when we shower, so we get hot/cold cycles after the first 2 to 5 minutes of showering. The builder/plumber/HVAC folks came and removed the water saving shower heads, and told us to take two showers at a time, if possible. Does that seem like another flaw in these combi units? the inability to heat a DHW flow less than 2.7 gpm seem like a flaw with shower head rated for <2gpm, and mixers set at some hot and some cold would mean you are rarely flowing even 1.5gpm through the DHW system when using a water-saving shower.
Thanks for all your help! I wish the folks taking my money were half as helpful as you lot of strangers!
The contractor chose the wrong equipment, and applied it to a poor design and doesn't understand what they are installing. You have a contractor problem plain and simple.
Personally I would hire a knowledgeable contractor to do a consult on what the proper design should have been, then hire an attorney to go against the installing contractor. The results are either he pays to have a proper system installed by someone who knows what they are doing or they rip out what you have to install the proper system.
And people wonder why contractors get a bad reputation. This is a perfect example.
EcoSteam ES-20 Advanced Boiler Control
Boiler pictures updated 2/21/15
https://www.facebook.com/media/set/?set=a.10202744301871904.1073741828.1330391881&type=1&l=c34ad6ee78
His last wood burning stove "contractor" burnt his house down because he never secured the flue pipe and the sections disconnected from each other inside the exterior wall!
Permits, training, certifications... lol... got a truck? You're a contractor
EcoSteam ES-20 Advanced Boiler Control
Boiler pictures updated 2/21/15
https://www.facebook.com/media/set/?set=a.10202744301871904.1073741828.1330391881&type=1&l=c34ad6ee78
Again, you have an incompetent, dishonest contractor.
You can choose to do what you want, but you cannot choose the consequences.
Then there is high output base board. Or add more of the same to what you have. The more emitter the lower the water temps.
With a mod/con boiler the goal is to always have the system side flow (secondary) greater than primary side (boiler). This assures that the boiler will always get the lowest return water temp possible for better boiler efficiency.