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Oil Boiler -) NG + new AC

Posted by permesso (My Page) on
Thu, Apr 28, 11 at 13:48

Hello all,

My wife and I have had enough of our 45 year old but mostly functional oil boiler (heat and DHW) and window air conditioners. We have cast iron baseboard heating elements that are in decent shape and we have recently replaced all windows with new good qualtiy Pella windows. We have no duct work and no natural gas hookup at this time. But I was able to confirm that we CAN get NG install at our house. We knew it would be an expensive undertaking but decide it was worth the cost to us especially with high oil prices and our poor DHW production in the winter.

I had 3 companies do estimates for a solution to get off oil for heating and install central air. We left the design options open (forced air vs hot water, gas vs. geo, etc). All 3 companies suggested that we stick with hot water heating with a ModCon NG boiler and then install seperate AC with new duct work. The duct work is a bit tricky in some spots (part of the house is on slab with rooms above) but do-able especially if only for AC. Eventually, all 3 concluded on the same basic duct design paths.

Only one company actually did a Manual J load calc and they even provided me the full report. After researching more and more, they seem to be doing and saying all of the right things. Not suprisingly, they are the more expensive of the 2 quotes that I have received. They seem to be the winner. They provided 2 options for heating and 2 for cooling. So, what I am hoping for is:

1) Opinions on if the overall design plan sounds right
2) Which equipment options you would choose. Specifically, is the additional cost of the more expensive units are worth it. I have read that a 2-stage AC unit may provide a more comfortable experience and that higher SEER will cost less to run. But the additional cost seems high and I don't think the cost may be worth it (at least for just a higher SEER rating).

Details:

Split-level/2 Story house (2 levels on one side of the house)
Near Philadelphia, PA
1519 sq ft room area (measured)
Heating Load - 46,962 Btuh
Cooling Load - 25,771 Btuh / 2.481 Tons (based on 77% sensible capacity)
(many other details in the Manual J report)

Options:

Heat --
Currently single zone oil boiler system. Quotes are to make it 3 zones including all hardware/plumbing. Also includes running NG lines to install area

1) 95% AFUE Triangle Tube PE110 Combi-Boiler w/ zoning system - $13,699
2) 90% AFUE Navien CH240 Combi-Boiler w/ zoning system - $11,499

Both appear to modulate to low enough to not be oversized for my load. Both would do DHW internally.

Cooling --
Include duct work, electrical all other stuff needed with a brand new install

1) Carrier 3 ton Infinity 21 Model 24ANA136 2 Stage AC, Infinity Model FE4ANF002 Air Handler, Infinity Control - $12,999
2) Carrier 2.5 ton Comfort 16 Model 24ACC630 1 Stage AC, Performance Model FV4CNF002 Air Handler, Edge Termidistat Control - $11,399

All have rebate options from my electric company be they are same no matter which I pick. Since I used the tax credit for my new windows in the last 2 years, my understanding is that I am not eligible for any further federal tax credits.

Your opinions or comments would be very much appreicated!


Follow-Up Postings:

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RE: Oil Boiler -) NG + new AC

if your gong to spend the money to get ductwork and A/C, you should upgrade to the A/C to a heatpump. Depending on how much you pay for electricity having a heatpump can be an efficient and comfy way to heat your house when its not very cold out (above freeziing). It will also protect you incase natural gas gets expensive. If you want to continue heating with the hot-water I understand since thats such a nice type of heat.


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RE: Oil Boiler -) NG + new AC

You may not get the savings from the conversion to NG unless you plan to stay in the home for a long time. At those prices you are looking at a 5-8 year payback depending on oil/NG prices.

Either way definitely keep the hot water heat. Heatpumps are not really effective in the northeast due to our cold winters and electrical rates are some of the highest in the US.

I would also ask about an indirect hot water tank instead of using a coil in the boiler. The indirect will give you unlimited hot water and it prevents having to keep the boiler running at all times to keep the coil hot. it may add about $1-2k to your price but its well worth it. the size is about the same as your NG water heater.


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RE: Oil Boiler -) NG + new AC

I agree with neo about getting a heat pump instead of straight AC unit.

I live in midwest and have 1931 home with hot water boiler. AC had been installed in the '80s. Last year finally konked out, and we replaced with a heat pump.

HOW DELIGHTFUL to have heat quickly when it's 67 daytime/45 nighttime. With only the boiler, it took a few hours before the house really would warm up to be comfortable on spring/fall days like this. We now have very inexpensive heat on days like this, and wow do we like it. We have ours on 1 Thermostat with the boiler. The heat pump cuts out at 40 degrees and switches over to the boiler at that point. That was where we ended up being the most comfortable. Others will run them at even lower outside temps.

Getting back to your system. Have you considered 80% boilers instead of the 90% condensing boilers? They are much simpler systems, with fewer complex parts and as they are cast iron, are less expensive. If you can get one into the space, I would look at the cost/benefit to that as well.

I agree with mnk about considering a straight hot water heater for bathing and cooking water. Just an option to also consider. Do the math and see what works out the best.


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RE: Oil Boiler -) NG + new AC

I really appreciate the feedback. In general, I haven't noticed it taking a long time to heat up the house. According to the HVAC company, doing forced air heating presents some additional challenges. They seem to think that the duct work that they can do is sufficient for cooling but may not be sufficient to heat properly. Or something to that effect. Two rooms are pretty difficult to get to with duct work. But, I doubt that would matter if it is used in conjunction with the hot water boiler.

But, even with a 80% boiler, I am guessing the total cost would go up on the system and it is already quite high. Also, we have fairly high energy prices as I understand it.

As for the DHW, juliekcmo my have misunderstood as mnk was talking about an indirect tank not a straight hot water heater. I do think indirect tank is a good route but I have heard good things about the triangle tube. This model actually has an integrated 14 gallon tank (tank in a tank) that I understand to be like a small indirect tank. Since we only have a single shower, I think this is a good fit.


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