Mod CON? Or Power vent 85%?

Gordy

Provided the emitters closely match the load in each zone. The best method to dial in ODR is turn the thermostat above desired set point. Adjust curve until the desired set point is reached. This will take a period of time, (weeks, or a season), and adjustments need to be made in small increments. This will insure the lowest supply temp required for the emitters. The thermostat then becomes a high limit device for loads such as solar influence, alternative heat sources, large gatherings.

Accurate heat loss calcs get you close to a starting point.

Suzook

NY_Rob said:

65K BTU's for a 2,200 sqft area works out to about 30BTU's/sqft.

I got this from Dana Dorsett from Green Building Advisor when I was first looking i to replacing my old system last year...

******************************************************
"It's better to NOT use xxBTU per square foot as a rule of thumb, but keep it in mind for sanity-checking other estimation methods.

For NY/NJ and southern New England for a 2x4 framed house 15 BTU/ft is somewhere near the middle of the bell curve, but its' a fat middle, and there are the exceptions that are truly north of 25 BTU/ft @ +15F, usually small houses with lots of window area, and an uninsulated foundation.

When discussing it with contractors present the fuel-use calculated number first stating that its based on weather & fuel use data, then if they protest point out that it's still 20 BTU per foot, which is a typical real-world number for code min houses in Anchorage AK (at -9F!)."
*******************************************************

After doing the calculations with my actual gas usage for a year, our local HDD's and my heated square footage... his "15 BTU/ft is somewhere near the middle of the bell curve" statement was pretty darn accurate as my house came in at 15.37 BTU/ft with a 50 deg rise at 15F DD.

The whole idea is to get your heating output to closely match your heating loss with the correct supply water temp, not to simply blast overly hot water through the radiators and cycle the boiler on/off many times per day. If your heatloss figure is not accurate the ODR curve won't match actual heatloss and efficiency will be out the window.

To illustrate the difference between supply water temps on a 2,200 sqft home with a 30BTU/ft heatloss and even a 20BTU/ft heatloss look at the calculations below:

You have 150ft of fintube right?
-To get 65,000 BTU's (at 30k BTU/ft heatloss) out of 150' of fintube you need 170F SWT (160F AWT).
-To get 44,000 BTU's (at 20k BTU/ft heatloss) out of 150' of fintube you need 145F SWT (135F AWT).

The ODR curves between the two SWT examples above will be drastically different. One will be in condensing mode for much of the heating season, the other won't.

Sorry, was late at work, pulling #'s out of my head. I have 2250 sq ft house, 36k btu heatloss.

NY_Rob

^ that sounds much more reasonable!

NY_Rob

Here's my settings on the "installer menu"... of course every home has different needs.
My ODR (OutDoor Reset) settings (items 4-7) can probably be "tweaked" for lower SWT (Supply Water Temp.) temps this winter because I added additional radiation since the spring.

With the ODR settings on pg 1- any time it's above about 19F outdoors I'm condensing.

Tim McElwain

I along with many others have enjoyed this posting. I have however received a number of phone calls from folks who are not necessarily trades people. They have a problem with the use of acronyms and abbreviations. I have been able to help most of them up to this point but it might help if a some place in the posting those are explained. It makes it more interesting for everyone. Thanks a lot and yes everyone in the world seems to have my phone number.

gschallert

you could always refer them to https://heatinghelp.com/systems-help-center/what-the-heck-do-those-letters-stand-for/

or even Google ;-)

Suzook

Thanks @NY_Rob
You really have been an amazing help! Couple of questions on settings.
Why turn down combustion rate? This have to do with your heatloss, and size of home? I am guessing it causes the boiler to run longer, and condense? And I am assuming the DHW settings wont work for me, as I have an aquastat on DHWH?

NY_Rob

^ I limit combustion rate because I want to prevent overshoot on my system. My shortest zone is 43' so when it's the only zone calling for heat... I don't need to throw 80K BTU's at it all at once- I'd rather heat it up a bit more slowly which is why I also have "Step Modulation" (37:CM) enabled. I wanted to extend run time even on the shortest zones.
IIRC when calculating the max combustion figure I used my 156' of fintube at 160F SWT which gave me 150F AWT (Average Water Temperature) which can radiate 380BTU's per foot for a total of 59,280BTU total radiation. If I limit my 80,000BTU boiler to 75% that gives me 60,000BTU's output... a pretty good match for my radiation at the highest temps I'll probably see.

The "Step Modulation" (37:CM) feature is very useful with low mass fintube baseboard. It "steps" up to max fire rate in six one min. increments rather than starting up at max fire rate. If you limit combustion, the "steps" are that much lower too.

If you notice... also have "CH Anti-Cycling Time" (16:Ft) enabled and set to 10min to help get my zones a little closer in sync with each other.

All the above was "tweaking" I did after observing my base system over time at varying outdoor temps. It was all done to custom fit my boiler to my house/radiation.
When you get your system running... you need to observe the burn times for your zones. If they're long, no need to make adjustments like I did. If they're short (under 10min) you'll need to address that- possibly like I did.

************************************************************

The DHW settings will still be in effect with an aquastat, except for the Temperature Setpiont (21:dH) and Differential Setpoint (22:dd) which will both be handled by your DHW tank's aquastat.

Suzook

Gas pressure test went without a hitch, inspector even did the final inspection of install!!!Just got to get the meter set on Friday, and I will be burning gas.

NY_Rob

Great news!
Congrats....

Suzook

^ You helped me get to this point. I'm thinking this may be the longest thread on this board???

NY_Rob

^ And some here (and some no longer here) helped me set up my system!

Pay it forward right?

A good group of guys here!

Suzook

^ Absolutely. I see in another post you added something to activate both or 3 of your zones in warmer weather to help condensing. Care to share?? Sounds like something I can benefit from.

NY_Rob

This is the $7 relay/thermostat that I use to combine two zones into one large zone on "warmer" (over 42F IIRC) days:
https://www.amazon.com/gp/product/B00GWFK7FA/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

You place it's thermistor probe outdoors in the shade, and program it to close it's relay when the outdoor temp rises above where your shortest zone would short-cycle.

You connect a lead from the "hot" wire terminal from each of your zone valves across the device's relay terminals. When it activates due to high outdoor temps- the relay closes and connects the "hot" leads from your zone valves.

Any time either of the zones call for heat now both zone valves energize giving you one large zone to prevent short-cycling.
As soon as the outdoor temp drops below your preset level.. the relay opens and the zones activate individually again.

It worked really well for me last season especially in the spring where we had 28F mornings with 65F afternoons.

Suzook

Well, I am burning gas!!!! I do have an issue with some air in my HW zone though...I made a mistake and have no air eliminator in it. I might have to bite the bullet and buy an additional dirtmag for that zone( yea...I know). I can't believe how fast this thing heats water!!! 10 mins to get 40 gallons in my HW heater to 140! Will I have any issues with some air in system for a few days???

JUGHNE

Usually 1 air eliminator/scoop will eventually take care of the entire system, unless you have severe upper loop that would trap air and keep the water from moving at all. In that case a manual key type vent for initial purge would cover it....just like a BB heater.

D107

If the water supply in a house is very hard--especially with things like lime--would that be problematic for a mod con? I know heating system water can be treated and is generally considered isolated but I've heard that mod cons are more sensitive to water issues.

Gordy

a combi, or tankless is vulnerable on the domestic side. A boiler no if you do your initial system fill with an exceptable water source meeting the installation manual recommendations. It's a closed system.

NY_Rob

Suzook said:

Well, I am burning gas!!!!

Congrats!

Suzook said:

I do have an issue with some air in my HW zone though...I made a mistake and have no air eliminator in it.

That's why I mentioned a few times the factory diagram is wrong and it needs to be piped differently.

You can still easily repipe to always include the dirtmag in the circuit any time CH or DHW loop is flowing.

D107

@Gordy re: modcon water supply. This may apply more in general than to Suzook's situation: it would be a closed system until there was a leak or a repair had to be made that required any water to be drained. Hopefully anyone who has a mod con --or any boiler--would have isolation valves on each circulator, expansion tank, etc. I don't believe I've heard of reliable whole house water filtering systems that would address this situation. So I guess the good water has to be pumped in to start and then a supply kept on hand for contingencies. It's fairly easy to get the house water tested by Rhomar--good to know what you have.

Gordy

Right. The Main thing is to stay in manufacturers outlined spec in the I/O manual. They usually have their exceptable limits on what they find to be potential issues with fill water quality.

Suzook

Water supply in my area is within HTP's guidelines. Not a problem for me. Unit is making my DHW now, and condensing! I am thinking I could have gotten away with a smaller Indirect. I have a 40 gallon. No big deal, always nice to have extra if needed.

Gordy

That's great. I wouldn't get to excited about the uft in the other thread either. Until that incident never seen such problems at least on this site.

Suzook

^ Yea, thats my paranoia setting in, LOL. I need to step back, and stop worrying too much sometimes. I am just a little leary with this "new" tech.

hot_rod

If you fill and purge a new system with hard water, you are going to coat the HX surfaces as the water warms and minerals come out of solution. Some of the minerals in water will fall out as you heat it, see bottom of tea kettle. Others will stay in solution as you heat water but still coat out surfaces as they circulate, the ones you see at faucet aerators, ideally you rip out ALL minerals + and - charged. Only RO, DI or distilling will do that.

A good example is when you pull an element out of an electric water heater. Yank it out after only several months of service and you will see at least a coating, possibly a thick build up. The less expensive, short high wattage density elements are more prone. Those long swirly type elements have more surface for the wattage and tend to handle hard water better, SandHogs, etc.

Here is a scale that shows the GPG or PPM for hard water classification. I'd guess 70% or more of the potable water in the US is hard or worse. The UK claims 60%

Softness test kits are inexpensive, test all boiler fill water! TDS also.

flat_twin

Condensing while making DHW? For the first couple minutes perhaps unless your boiler water temp setting for DHW is set pretty low. What are your DHW settings for boiler temp? Indirect aqua stat setting? Mixing valve?


I'm happy that our recently installed 40 gallon indirect can recover more quickly than it can be used up while the shower is in use. I also wondered initially about a smaller indirect for just two people and one shower but we can make several short hot water draws including a quick shower without making the indirect call the boiler for heat so maybe it's about the same. I think the larger tanks have less standby temperature loss due to their mass so that helps some too.
FWIW our DHW is set at
boiler temp 155
aqua stat 140
mixer to
faucets 125

Got my first NG bill with no heating, only DHW costs. We used 6 CCFs in June, $7.70 for gas / $8 service fee. To be fair we were also away for a week but still that's not much for operating a NG indirect.

Gordy

There can be some condensing on start up of a dhw call. Depends on storage temps as to how long that happens.

Suzook

flat_twin said:

Condensing while making DHW? For the first couple minutes perhaps unless your boiler water temp setting for DHW is set pretty low. What are your DHW settings for boiler temp? Indirect aqua stat setting? Mixing valve?

Boiler temp 130, Aquastat 120

Gordy

Like that.

Gordy

Not a tank storage temp conducive in keeping legionella in check however.

Suzook

^sorry, on my phone Boiler temp of 140

Gordy

On cold start any boiler will condense for a short period of time until steady state is reached especially if the storage temp is 120.

Suzook

Quick update. Boiler running great! So in order to get my co, I need an electrical inspection. Uhmmm, the boiler plugs into an existing outlet! So now I need to waste a vacation day, and $200 for the inspection. Unreal.

Gordy

Separate circuit with disconnect?

Suzook

^No. Boiler in new spot, but used old feed from boiler switch to feed an existing outlet where new boiler is.. Boiler has a plug, and a switch to turn it on and off too.

Suzook

So el inspection was a joke, guy walked in, and right out. Oh well, I passed!!! I haven't got around to installing another dirtmag/air eliminator on my HW zone. I do have a little air I can't purge. Is this a big deal? Any issues I could cause to the boiler??

Gordy

How much have you actually been running it? Have you even had it up to operating temps for a long period? I'd see if the air finds its way to the removal device once you are operational in the heating season. You should only need one air separator for the system.

Air comes out of solution as water gets hotter. The higher the pressure the more air will stay in solution.Finally a little dawn dish soap can help get trapped air moving to the separator.

NY_Rob

You could try by running 34:AP (pump-purge mode) for the CH circuit till it's quiet, then run it for the DHW circuit, then run it for the he CH circuit again... maybe multiple times for 30min or longer till both circuits are quiet.

The problem is both circuits are completely isolated from each other (and never run concurrently) with only the three gallons in the HX in common. With air in the DHW circuit not passing through the air strainer, you have to mix that in with the air free water in the spaceheating circuit three gallons at a time via the HX and then purge that from the larger spaceheating loop which does pass through the air strainer. During heating season that would happen naturally several times a day... but with no calls for spaceheating during the summer- it will never happen.

Personally, having used this boiler for over a year now- knowing how sensitive it is to air... I'd re-pipe to have both the spaceheating and DHW loops run through the Dirtmag 24/7/365. Keep in mind that you only run the spaceheating loop six months of the year around here so for the other six months you'll be bypassing the 3-function Dirtmag for all your DHW heating the way it's piped currently.

Gordy

Nothing is isolated. Air should end up at the sep.

NY_Rob

Unfortunately, the factory recommended layout (in the I&O manual pg 37) by HTP doesn't account for an off-season install and completely leaves the air separator out of the DHW loop. Proof that the factory layout is flawed is that the OP has been running his boiler for 2.5 weeks now and still has air in the DHW loop....
I also had the same problem with my (June install) HTP UFT when I followed the factory diagram.

If you only use the boiler for DWH for the first few months after the install... how do you get air out of the DHW loop with the factory recommended layout?