Gas conversion-Heat loss-Second opinion

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Old 07-25-14, 07:04 AM
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Gas conversion-Heat loss-Second opinion

Hi all,

I haven't been on the forum lately due to warm weather but hope you are all well.

After hearing about my successful gas conversion last year, a neighbor asked my opinion about converting his 20+ year old, forced hot water oil system (179KBTUH in, 140K BTUH out). So I walked through a heat loss calc with him. According to our calculation his 1224 s.f., 2-story house built in 1931 with recently installed attic insulation, blown-in cellulose in walls and all new replacement windows has a heat loss of 25771 BTUH at 10 degree design temperature. (We are near Boston).

Although this is waaaaay lower than his existing system rating I am not surprised based on my own experience and what I have learned from this forum.

I think the Alpine ALP080BW-2T02 rated 16000-80000 BTUH is a good choice for him with the National Grid rebate. His existing chimney does not have a SS liner but access to the outside for high efficiency venting is easy. Gas is already in the house and last year he had a 1.25 inch new service line installed when National Grid upgraded the main in the street. There is an existing drain in the basement for sink, washer, and toilet so handling condensate should not be a problem.

The house has 391 s.f. of CI radiators for emitters on one zone. The piping splits into two halves so he could possibly zone it for north-south exposures. Currently the second floor overheats because the original radiators were sized for no attic insulation and the attic is now fully insulated (I'm guessing to R30+). We are going to see if we can valve them down or reduce the water volume in them if still overheating after the new system is in place. I think however the new system will heat the house satisfactorily with 145 degree or less water so the overheating (overshooting) may not occur to the extent that it does now

What do you think. Are we on the right track. He is gathering this info so he will be able to have knowledgeable conversation with installers.
 
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Old 07-25-14, 03:33 PM
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Heat loss is probably about right. My 'rule of thumb' of 25 BTUH/SF puts it at about 30K. If the insulation is as good as you say, 25K could be right.

Alpine ALP080BW-2T02 rated 16000-80000 BTUH is a good choice for him with the National Grid rebate
I know next to nothing about the Alpine, but depending on the rebate, it seems it could be a good choice. Being that NG is 'pushing' them, there should be no shortage of techs that understand them and their maintenance needs.

Is there a model they are pushing that has a lower top end and mods down lower?

Otherwise I would select Triangle Tube.

handling condensate should not be a problem
You know about the need for neutralizer I think...

The piping splits into two halves so he could possibly zone it for north-south exposures. Currently the second floor overheats because the original radiators were sized for no attic insulation and the attic is now fully insulated
Too bad it's not easily zoned for up/down!

We are going to see if we can valve them down or reduce the water volume in them if still overheating after the new system is in place
Good luck with that. It's usually a 'no joy' experience to attempt to balance heat output by messing with flow.

Depending on how they are piped ( in series? home runs? Monoflo tees? reverse return? ) you may not be able to adjust the flow anyway.

If the rads are piped anything but in series, you might consider TRVs (Thermostatic Radiator Valves) for the hotter rooms.

How would you propose to reduce the water volume in them?

I do think you are correct that the cooler water will mitigate the overshoot to some extent, if not entirely.
 
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Old 07-25-14, 05:28 PM
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My opinion would be to zone the up and down.. Do whatever it takes. Find the splits and run a line from there, the second floor to the boiler.. I would make this a priority.

But find out from troops comments here
Depending on how they are piped ( in series? home runs? Monoflo tees? reverse return? ) you may not be able to adjust the flow anyway.




It will never be comfortable one zone with two floors.

Last I dont know what the alpine costs but I would lean towards the peerless purefire.. About $3k

Peerless® PUREFIRE®

16-50k btu Stainless steel and has the built in neutralizer .. Also sealed combustion...

Otherwise I would select Triangle Tube.
There are a lot of recommendations for them, although I have never seen one in my area. And thats throughout my whole career. 30 years at least..

The solo is a 16-60k btu Probably about $3K

Prestige Trimax Solo Series | TriangleTube


Couple either of them with a Indirect supor stor contender ssc35. These only need 53k btu for full output.. About $700 bucks

SuperStor Contender Indirect Water Heater


All my opinion of course. And since natural gas from oil you may want to save some money and put a standard boiler in.. IMO costs less, less maintainace and better payback. Less stuff to go wrong. Although the rebates look appealing if you do the math you can figure it all out..

Whats the water quality? Not on a well? City water?

Anyway lets say a burham series 2 like this.. $1600..?? Oh my.. Since sandy boilers have went up through the roof.. This boiler used to be had for $1100..


P202-EI-NG - Burnham P202-EI-NG - P202 27,000 BTU Output, Electronic Ignition Cast Iron Boiler (Nat Gas)


Just a thought...




Refreshments all around....
 
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Old 07-28-14, 11:59 AM
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Thanks for your expert opinions. Makes me feel all warm and fuzzy now about our conclusions as I hope my neighbor will feel next winter if he goes ahead with this project.

depending on the rebate, it seems it could be a good choice
NG price in MA for the Alpine ALP080BW-2T02 Energy Star HE stainless steel condensing boiler is $2,869.02 including sales tax. The rebate is $480 gift card and $1500 mail-in rebate. That makes the net price $889.02. Why would you not take advantage of that? This is the lowest rated one they have.

My comment about condensate drainage refers to the discharge AFTER neutralizing. In answer to Lawrosa the feed water is high quality city water.

My neighbor has asked me to take a look at something else this week and I will investigate the piping further when I am there. The basement piping is large diameter black steel and the emitters are all CI radiators so I don't think we have to deal with monoflow tees or series connections. (The second floor units may be on common risers with the first floor radiators but probably not since they are not always located directly above.) TRVs are a definite possibility for the warmer rooms.

you may want to save some money and put a standard boiler in
That would require a new SS chimney liner and add about $2500 to the cost.

Couple either of them with a Indirect superstor contender ssc35.
His current HW heater is a direct gas fired unit, fairly new and in excellent condition. Indirect HW will be a future consideration.

How would you propose to reduce the water volume in them?
I will give you a short reply here based on my own experience but it might develop into a discussion that deserves it own thread.

In my own living room I have two very large CI radiators (180 s.f. total) both in cabinet enclosures. In an adjacent foyer that is open to the LR there was a small radiator (about 16 s.f. as I recall) that has been removed. Even before the conversion that room was greatly overheating. Part of the reason is that I have a "whole house" humidifier that blows through one of the large emitters (and maybe that's even another thread)--it acts like a fan-coil unit and increases the heat output of the emitter enough to notice. After the house was insulated and weatherstripped the need for so much radiation was obvious. I removed the small radiator in the foyer but still needed to reduce the heat. Recognizing that my system builds up air in the radiators from time to time I was bleeding them annually. So I decided just to not bleed those in the living room for a while and see how it went. Still plenty of heat.

So I tried this:

Closed off as much of the system as I could to isolate the LR radiators.

Connected an air compressor to the bleed valve at the top of the radiator by slipping a plastic tube onto the bleeder valve neck. (They are an old fashioned type that even have a slight ridge at the outlet like you would connect a rubber hose to on a faucet--no threads just a flare to slip a tube onto.)

Set the air compressor for low pressure (about 10 #) so as not to "overcharge" the expansion tank or blow the relief valve.

Opened the boiler drain valve and let out a small amount of water.

The idea was to drive some of the water out of the selected radiators.
Less water = less flow volume = less heat.
It seems to have worked. The room temperature now tracks nicely to the rest of the house.

The supply and return connections are both at the bottom of the radiator and the piping is large (low flow velocity) so the likelihood of purging the air out of the radiator and into the system is low. Probably not the most scientific way to do it but worth a try.
 
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Old 07-28-14, 12:40 PM
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Make sure to flush the system good to get all the crude out the rads..Install a strainer..

Or better yet fore go the P/S piping and strainer and install a hydrolic separator.. You get air vent/ strainer all in one..

http://www.taco-hvac.com/uploads/FileLibrary/100-76.pdf

Also a 3 speed pump.. You may need more flow if the end room rads dont get hot enough.. At least youll have the option...
 
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Old 07-28-14, 03:00 PM
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gas conversion-heat loss

Have you considered an out door reset control which will pretty much eliminate over heating. I would like to recommend the Viessmann Vitoden 100w as it is condensing and comes with an out door reset . The more heat emitters the lower the supply temperature and the lower the return temperature and the higher the system efficiency as the return temperature establishes the boiler efficiency. There is a 1% fuel savings for every 3 degrees f the system water temperature is lowered .This is what I have learned from reading articles in HPAC magazine .
 
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Old 07-28-14, 04:25 PM
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Don't all mod-cons come with outdoor reset?

Yes, I believe that they do and the Burnham Alpine is no exception, which he can get for under a grand after rebates and beer cards?
 

Last edited by NJT; 07-28-14 at 07:01 PM.
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Old 08-02-14, 09:23 AM
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Regarding the design load calc, take it with a grain of salt, especially if you didn't run a blower door. Old houses especially can have wide variation in air infiltration which can have a big impact on design load, and you don't mention air sealing the attic flat. In any event, the boiler you propose has plenty of power for this application - just make sure to pipe it for a future indirect DHW. For single zone, especially, it might be nice to have interior temp feedback to the reset curve - but I'm not aware of that being available for your application, so that's a topic for another day.
 
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Old 08-03-14, 06:59 AM
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I could see a problem with rads half full, oxygen, turbulence, and maybe a little noise. I would try to reduce the air flow through the rad. An extreme remedy, remove a few sections from the problem rads.
Just saying.
Sid
,
 
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