Hi,

I just finish building 2 story ICF house in Connecticut. I had someone run Manual J for me with following results.
1st floor heating 14,583, cooling 7,098
2nd floor heating 16,024, cooling 8798

I also have done my own Manual J (CoolCalc) and BeOPT.

CoolCalc Manual J.

• Per room, 1st Floor heating 18,101
• Per room, 2nd floor heating 9,618
• Total Heating 33,509, Cooling 21,534

(I don’t understand why per room sum of outputs does not add up to final CoolCal output, is this bug in CoolCalc? (18,101 + 9,618= 27,719)
My 1st and 2nd floor dimensions are equal except I have more inner rooms with no outside wall exposure on the 2nd floor (laundry, walking closet, hallway, bathroom) these rooms have very small load which I think is throwing this imbalance between 1st and 2nd floor load. 1st floor more than half floor is 1 open space.

BeOPT My own beopt calc,
House heating 28,900, cooling 18,000.
I’m planning on installing propane on demand boiler/water heater (Rinnai, Navien, Buderus, etc)

I have couple questions:
1. Which boiler would be good for family of 4 with occasional additional 2 to 4 occupants? BTW I’m on the well at 3.5 GPM.

2. I want to install underfloor in joist heating. How should I limit the output from PEX as at max rate 35 btu per foot I will be overheating my house. I need approximately 12 btu per foot.

3. Should I only have 1 run of ½ PEX per joist with heating shield to limit amount of PEX and control rest with water temp and flow?

4. Here is my main question. I’m not sure how I can calculate ratio of footage/temp/flow to get right output? Is there a formula that I can use for this?

BTW I’m working with heating/plumbing supply house to design my heating system but I’m not having full confidence that they are doing this correctly. I would like to educate myself so I can design or at least confirm someone else calculations.
Any help or direction to some source would be very much appreciated.
Thank you.
Jerry.

Yes, I would suggest that you first get well-educated on how to design a HR heating system before proceeding with anything. The best way to accomplish that is to get a copy of John Siegenthaler’s “Modern Hydronic Heating”. You will find the proper design methodology and engineering equations needed to successfully accomplish this design mission.

We have information and free software on our website for DIY HR design. It is much easier to use HR design software than working it out with a pencil. You definitely do not want someone who is not well-versed in HR design (e.g., typical plumber, typical HVAC company or HR component vendor) to design your HR heating system or you will likely end up with hot and cold areas and/or an overly complicated HR system that unsuccessfully attempts to remedy these problems.

The first step is always an accurate room-by-room heat loss analysis (ACCA Manual J8 or ASHRAE equivalent).

I don't think you have to worry about over heating because you are going to have some type of thermostat to control it. Turn the pump(s) on for heat and off for no heat.....

Not a fan of the complexity of a broiler....this can be done with a good old fashion tank hot water heater for quarter to half the cost.

Others will argue that. Good Luck and ask questions.

Some pointers are to figure out your loop lengths and keep them around or under 200 feet.

Why didn't you plan for heated floors from the start?

Rule of thumb on heating is you cannot have too much capability. It turns off when you don’t need it. My radiant system is run by a boiler about 3x the size of my heating load (and I have radiant in the garages so I have that option if I want to melt my tires). Since the boiler modulates and heats a buffer tank it can run a low load or a high load when needed. I have thin slab radiant and I can run the water temp around 95F most of the winter. When we are below zero I turn the valve up to 105F.

Under floor radiant requires much higher temperatures. In my mind that was not a good option. If you are doing radiant you want to do it right. The control setup and design takes a bit of thought. I’d recommend not to overlook that.

If your home is efficient the radiant won’t run all the time, so the floors won’t always be warm, but the house will be very comfortable.

Rule of thumb on heating is you cannot have too much capability. It turns off when you don’t need it. My radiant system is run by a boiler about 3x the size of my heating load (and I have radiant in the garages so I have that option if I want to melt my tires). Since the boiler modulates and heats a buffer tank it can run a low load or a high load when needed. I have thin slab radiant and I can run the water temp around 95F most of the winter. When we are below zero I turn the valve up to 105F.

Under floor radiant requires much higher temperatures. In my mind that was not a good option. If you are doing radiant you want to do it right. The control setup and design takes a bit of thought. I’d recommend not to overlook that.

If your home is efficient the radiant won’t run all the time, so the floors won’t always be warm, but the house will be very comfortable.

If you actually know how to properly design HR floor heating, you can have the same temperature everywhere (rooms with many windows and rooms with no widows) and accomplish it with one thermostat and one supply temperature to all the circuits. The HR design determines the proper PEX spacing and circuit flow rates such that the required and variable heat gain needed for each square foot is provided consistent with the room-by-room heat loss analysis and the actual heat loss. As you deviate from a proper HR design, more thermostats and mixing valves will be required, and you may still find that you have areas that are under or over heated and your heat source will always be running because some area will always be calling for heat.

In an energy efficient home, you will never have warm floors. You just won’t have cold floors. Typical HR floor surface and supply temperatures in an energy efficient home are 72F and 85F, respectively. If you are doing concrete slab HR floor heating, it is all the more important to get the HR design right because of the long time delay associated with these high thermal mass emitters in reaching the required surface temperature that provides the required heat gain consistent with the actual heat loss.

Hot water heaters or any heat source that is not rated for space heating are not allowed where we operate.

At CT style propane & electricity pricing you'll be better off going with cold climate heat pumps, correctly sized for the heating load, which will also cover your cooling loads. (Do NOT go with the "ductless head in every room" approach, which will grotesquely oversize the system.) What is your 99% outside design temperature?

sailawayrb has it right- at your heat loads you won't ever have warm floors, just less-cool floors. If you still want to take the chill off the floors, a small electric boiler operated on a floor thermostat can work, but let the heat pumps do the heavy lifting.

Combi boilers are a terrible choice for low heating load/moderate-to-high hot water needs. If a mod-con boiler or combi boiler has a minimum firing rate half the design heat load or higher it's not really a good fit. There is nothing about the description that points toward a combi boiler (or any fossil-burner really) as being a good fit here, though it could be MADE to work. The minimum firing rates of combi-boilers big enough to deliver reasonable hot water service is much higher than ideal for your zone loads, but there are some mod-cons that can go low enough to modulate at least some of the time.

This is one where you should probably just lose the propane tank and go all-electric using better heat pump technology.

Even though your well is 3.5gpm your maximum water flow won't be limited to that. A 199KBTU combi boiler will only be good for about 5 gpm on tub fills in winter at CT incoming water temps. A tank can deliver at whatever rate your system pressure will allow. A heat pump water heater sized for the biggest tub you need to fill can peel off some of the sensible cooling load and provides dehumidification during lower cooling load summer days.

Hi,

Thank you for all responses. I been busy installing Pacific Energy FP30 fireplace and doing some DWV plumbing so my reply comes few days after your responses.


Sailawayrb,

Thank you for book recommendation. Just started to look thru the book and I did some heat loss calculations. It feels so empowering to know and understand how the inputs and outcome numbers are related. This books is awesome and how is written it makes one of the best textbooks.

I just wish I have bought real book or epub version instead this stupid vbk format from textbooks.com that needs its own reader and you can only print 2 pages at a time with not very good quality even at price difference of 100.00. But I will manage.



Dana,

I already have 1000 gal tank in ground I will be using this for cooking, hot water and I was thinking heating.

My reason for propane was that I can fill up once a year when prices make economic sense, for electricity I have to pay whatever current rate is in given month.

But I do love mini-splits and I'm planing to install 2 ducted units (basement and attic) to cool house and 1 head unit in bonus room over garage that is attached to the house but not part of the main house. This is 2x6 construction. Boss is not approving wall units in other house areas.

I'm really intrigued by your heat pump comment. I didn't think this was economical option as I assumed in temp below 30's the COP for AHP be at 1.0 however it seem that some of these can run at COP 2.0 well into very low temperatures.

If this is really truth and AHP can achieve COP of 2.0 then my cost per MMBtu could be lower by $10.00 vs. propane. Which at 66+ annual usage of MMbtu calculates to a difference of around $625.00. Now if I can put solar panels this would go even further.

On other hand we like the feel of that radiant heat on these very cold days and nights. I do think that I may need other form of heating besides AHP in my town for CO.

Since I already have propane thank do you have any recommendation what would be my best way for radiant heat, ideally radiant floors and hot water if not COMBI heater?


Thank you.

Cold climate heat pumps with vapor-injection scroll compressors can run at a COP of ~2 even at -10F outdoors, and COPs of 3 or better if modulating in their sweet-spot levels at +10F to +30F. These aren't very much like your grandma's single stage R12 heat pumps of the 1980s.

Mitsubishi's new mono-directional MLZ ceiling cassettes designed to fit between 16" o.c. joists can be married to cold-climate multi zone compressors completely avoiding the wall-blob look. Those can also be married to fully modulating single zone compressors, but alas not a cold-climate single zone compressor. :-( (Maybe next year...) eg:

http://meus1.mylinkdrive.com/files/M_MLZ-KP12NA_SUZ-KA12NA2_SUBMITTAL-en.pdf

http://meus1.mylinkdrive.com/files/MLZ-KP18NA_For_MXZ_MULTI-ZONE_SYSTEMS_Submittal-en.pdf

There are also floor mount versions of single zone mini-splits that can be tucked into partition walls & cabinets, etc.:

http://meus1.mylinkdrive.com/files/MFZ-KJ18NA-U1-MUFZ-KJ18NAHZ-U1_ProductDataSheet.pdf

There are also ducted mini-splits from Fujitsu using the right type of compressor, but without pan heaters to clear defrost ice build-up aren't rated for extended operation below -4F. They still work at lower temps and are fine for use in CT if you're willing to check the pan drain for ice plugs when it's consistently below freezing for a week or more. (I know of a few people in central MA heating/cooling with them.)

http://www.fujitsugeneral.com/us/resources/pdf/support/downloads/submittal-sheets/18RLFCD.pdf

With any modulating heat pump solution sizing it correctly is critical to getting the performance out of it. This is even more true if going with a multi-zoned compressor, since the cassettes/heads don't fully modulate with load the way single-zone mini-splits do.

I'm partial to fire-tube modulating condensing boilers with big turn-down ratios for hydronic radiant floors that will run nearly 100% duty cycles during the depths of winter for maximum efficiency. The fire -tube boilers can usually be set up to be pumped direct rather than primary/secondary (which is almost essential for combi-boilers) and are fairly forgiving for DIY installations.

A low cost but decent unit that would cover the heat loads of 95 out of 100 houses in the US is HTP's UFT-080W, which can modulate down to about 7500 BTU/hr out in condensing mode, but over 70K at high fire at non-condensing temps. It's pre-designed with a secondary port and controls for managing an indirect water heater. You're only a few hours drive from their national HQ, and could heave the thing through their front window if it craps out on you and you can't get satisfaction, but it's been out there for a few years now with a largely favorable reputation.

Yes, I would second the HTP UFT-080W as a great mod con gas solution. We haven’t seen hardly any issues with HTP and when we did, their customer support was stellar. Using a combination of mini splits and HR floor heating is good approach too, especially when you need AC. Please be sure to accomplish the heat loss analysis before sizing and selecting the heat source(s).