Need help choosing heat source

[tomb9712]

Ok here's my dilemma I have a 3 story 30 x 45 garage and the second floor has PEX in the floor radiant heat tube installed but no heat source for the tubing as of yet. I have no natural gas in my area so my options are propane and electric.

Below are the specs of the garage:

Outside walls are 10" thick cement block with a 6" air gap and then R21 fiberglass insulation. The walls themselves are 1/2" plywood all the way around the building. The inner walls are all R15 fiberglass insulation. The ceiling is 1/2" hard board insulation with R30 blown in insulation above that.
The PEX tubing is stapled directly to the floor with a reflective barrier below it with R21 fiberglass insulation below that in the ceiling of the first floor. The ceiling height is only 6' 6" high not the standard 8'.

The second floor is set up into 4 separate zones.
Zone one is roughly 400 square feet and would need to be heated to normal room temperature.
Zone two is roughly 300 square feet and would need to be heated to 77-79 degrees.
Zone three is roughly 200 square feet and would need to be heated to 72-75 degrees.
Zone 4 is roughly 75 square feet with a 5' 5" ceiling height (yes it's really low) and needs to be heated to 86-89 degrees.

I'm located NE PA so winter here can be pretty brutal. The current overnight is about 10 degrees.

I also need potable hot water for a bathroom sink, and a wash basin for cleaning things. The potable water will not be used too much.

What I need help with is figuring out what type of unit to heat the hot water. I've been told an electric hot water heater in a closed loop system would be best by one local plumber and an electric boiler in the same set up by another. Yet another plumber suggested a propane boiler with an electric on demand hot water system for the potable hot water. I'm so confused and have no clue what to do. Any help would be great. If you need more info please let me know. Thanks Tom

 

[matt_i]

A conversion I looked up is that 1 gallon of propane is energy equivalent of 27 kW-hr. Seems like propane sells for around $2.00/gal so 7.4 cents per kW-hr. There is the efficiency of the burner to be thrown in also, which I didn't do. If you have an 82% efficient appliance you get only ~22 kW-hr of heat energy to use, so closer to 9 cents per kW-hr.

You'd have to check your existing electric bill but my guess is most are going to be higher than 9 cents per kW-hr. Its around 15 cents per kW-hr here.

It seems like you are going to heat this regularly, so I would go with the lower unit energy cost. There's of course the weight of the installation costs, presumably electric needs no venting and whatever the heating appliance costs up-front to also be considered.

Just some info to help you make a more numerical decision.

 

[tomb9712]

It will need to be heated 24/7. Checked on the cost of electric and it's 12 cents per KW here. Propane works out to be 10 cents per KW so not a huge difference.

 

[tomroblee]

In the principles of operation there isn't much difference between a water heater and a boiler. A boiler is probably designed better for the long run times required by radiant heat and may be more reliable.

In the event of equipment failure, it MIGHT require more lead time to get a replacement boiler.

An electric water heater or boiler is probably more efficient in energy usage than a propane boiler.

I'm guessing that your cost per Kwh were based on current prices. Propane prices seem more volatile than electric costs.

Propane requires a tank. Getting a huge tank will be more expensive than a smaller tank---but may allow you to only refill in the summer when prices are lower. "Renting" a tank from you supplier may require the least cash up front, but will lock you into using the same supplier for a number of years.

Do you currently have sufficient electric service at your garage for electric heat? There could be significant costs if you have to upgrade your service--especially if you would need to add a second meter.

 

[thickhead]

Is an oil burner out of the question?

 

[theoldwizard1]

Propane condensing boiler. Small, under sink, electric "on demand" water heater.

 

[tomroblee]

You say that it is a three story garage. Is the ceiling height 6 1/2' on all three floors? I'm not sure from your post whether the first and third floors will be heated and (if they are heated) to what temperatures.

I'm not well versed in radiant heat, but I can see some sizing issues with a total radiant heat system. Multiple zones sound good in theory, but designing and operating them can be difficult when you have a large single heat source and tiny zones---especially if the smallest zone is to have the highest temperature.

When ONLY the 75 sq. ft. zone is calling for heat, I would think that the controls would try to direct the entire output of your water heater or boiler to that zone. Heating only a low ceiling bathroom sized room with a boiler that was sized to heat a three story building doesn't sound very efficient.

 

[cork]

I can't help much with the heat, but I'm curious why the need
For the consistent high temperatures?

 

[matt_i]

It will need to be heated 24/7. Checked on the cost of electric and it's 12 cents per KW here. Propane works out to be 10 cents per KW so not a huge difference.

Seems like a 20% difference is not insignificant to me. Just saying over 1 kW-hr its no big deal but when you are pouring out 100,000 kW-hr (over time, additive, don't know how many years it will take to get there) the difference of 0.02 x 100,000 kW-hr = $2000.00

As I said before its not all "free money" to be harvested because the cost of the install could be different, but the "2 cent conveyor" isnt ever going to stop.

 

[tomb9712]

In the principles of operation there isn't much difference between a water heater and a boiler. A boiler is probably designed better for the long run times required by radiant heat and may be more reliable.

In the event of equipment failure, it MIGHT require more lead time to get a replacement boiler.

An electric water heater or boiler is probably more efficient in energy usage than a propane boiler.

I'm guessing that your cost per Kwh were based on current prices. Propane prices seem more volatile than electric costs.

Propane requires a tank. Getting a huge tank will be more expensive than a smaller tank---but may allow you to only refill in the summer when prices are lower. "Renting" a tank from you supplier may require the least cash up front, but will lock you into using the same supplier for a number of years.

Do you currently have sufficient electric service at your garage for electric heat? There could be significant costs if you have to upgrade your service--especially if you would need to add a second meter.

I have 3 local places I can get an electric or propane boiler quick if I need it right away would pay way more then online prices but can get it right away.

Plenty of electric service that's not an issue at all. Was previously set up as a metal fabrication shop/semi truck garage.

 

[tomb9712]

@ thickhead Yes oil is out of the question. Getting a tank put in would be way too expensive.

 

[tomb9712]

Propane condensing boiler. Small, under sink, electric "on demand" water heater.

That's what I was thinking but I've been told conflicting info on running a propane boiler with the pex tubing directly attached to the floor. Was told since the boiler runs at about 160 degrees the wood floor would be very hot and most likely start to warp due to the heat. No clue if that's true or not but would hate to spend $3000 on a boiler and find out it won't work.

 

[tomb9712]

You say that it is a three story garage. Is the ceiling height 6 1/2' on all three floors? I'm not sure from your post whether the first and third floors will be heated and (if they are heated) to what temperatures.

I'm not well versed in radiant heat, but I can see some sizing issues with a total radiant heat system. Multiple zones sound good in theory, but designing and operating them can be difficult when you have a large single heat source and tiny zones---especially if the smallest zone is to have the highest temperature.

When ONLY the 75 sq. ft. zone is calling for heat, I would think that the controls would try to direct the entire output of your water heater or boiler to that zone. Heating only a low ceiling bathroom sized room with a boiler that was sized to heat a three story building doesn't sound very efficient.

First floor has an 8' 3" ceiling height and is heated by the heat created by several large freezers, refrigerators, and electric wine fridges in one half. It stays about 60 degrees. The other half does not need heat as it's just storage right now it's about 48-50 degrees. We have day time temps in the 20's and night time temp about 10 degrees.

Third floor is not heated at all right now as it's unfinished till spring/summer. Between the third floor/ceiling of the second floor has R30 blown in insulation. Not sure the ceiling height there. If I had to guess i'd say just under 8'.

The smallest zone is actually the furthest from the heat source. . The pex run for that room is 298 feet round trip but because it's so small and so well insulated it should stay hot for a long time and not call for heat too often. We have a 60 watt light bulb in there now and it warms the room to 66 degrees. The lines for the small room also run parallel to the other zones so when that line calls for heat it will also transfer some heat to the other zone lines as well so not too wasteful, or at least that's the theory anyway.

 

[tomb9712]

I can't help much with the heat, but I'm curious why the need
For the consistent high temperatures?

I professionally breed and keep reptiles. It's easier to manage everything with warm/hot rooms, and a lot cheaper too.

 

[tomb9712]

Seems like a 20% difference is not insignificant to me. Just saying over 1 kW-hr its no big deal but when you are pouring out 100,000 kW-hr (over time, additive, don't know how many years it will take to get there) the difference of 0.02 x 100,000 kW-hr = $2000.00

As I said before its not all "free money" to be harvested because the cost of the install could be different, but the "2 cent conveyor" isnt ever going to stop.

Good point. I wasn't thinking over the term of a year or longer.

Was told by a friend I should be eligible for a business rate on electric and propane as the garage is used solely for my business and has a separate electric meter (or if I go with propane will have separate tanks) from the residence on the property. Might be cheaper but won't know till I can call them and talk to someone.

 

[tomroblee]

Just for information purposes, the government tracks various fuel source prices by state, by week. I have no idea how these might relate to your specific situation.

http://www.eia.gov/opendata/qb.php?sdid=PET.W_EPLLPA_PRS_SPA_DPG.W

Electric rates seem to be getting more complicated every year. When trying to decide between various fuel sources you need be sure that you are pricing electricity at the marginal rate for additional usage. In my city (Indianapolis), there is a fixed monthly charge, one (higher) rate for the first 500 KWH per month, a lower rate for usage over 500 KWH, and even a lower rate for usage over 1000 KWH if you have electric heat. In addition, there are a long list of "riders" which allow the utility to adjust rates monthly for things like changes in their fuel costs, costs associated with environment compliance, etc. (The purpose of the "riders" is to allow the utility to adjusts their rates as their costs vary without having to go through a full blown rate case.)

With your additional information I have a better idea of the heat loads involved. Your situation certainly isn't typical for members of this forum.

If you are trying to closely control the temperature of the second floor to raise reptiles, supplying heat in very cold weather sounds like the easier part. As the weather gets more moderate to downright hot, you may be wanting to heat your hot zone while supplying no heat (or even air conditioning?) to the other zones. Keeping a boiler operating 365 days a year just so you can heat a 75 sq. ft. zone a long distance from the boiler doesn't sound very efficient.

 

[tomb9712]

Just for information purposes, the government tracks various fuel source prices by state, by week. I have no idea how these might relate to your specific situation.

http://www.eia.gov/opendata/qb.php?sdid=PET.W_EPLLPA_PRS_SPA_DPG.W

Electric rates seem to be getting more complicated every year. When trying to decide between various fuel sources you need be sure that you are pricing electricity at the marginal rate for additional usage. In my city (Indianapolis), there is a fixed monthly charge, one (higher) rate for the first 500 KWH per month, a lower rate for usage over 500 KWH, and even a lower rate for usage over 1000 KWH if you have electric heat. In addition, there are a long list of "riders" which allow the utility to adjust rates monthly for things like changes in their fuel costs, costs associated with environment compliance, etc. (The purpose of the "riders" is to allow the utility to adjusts their rates as their costs vary without having to go through a full blown rate case.)

With your additional information I have a better idea of the heat loads involved. Your situation certainly isn't typical for members of this forum.

If you are trying to closely control the temperature of the second floor to raise reptiles, supplying heat in very cold weather sounds like the easier part. As the weather gets more moderate to downright hot, you may be wanting to heat your hot zone while supplying no heat (or even air conditioning?) to the other zones. Keeping a boiler operating 365 days a year just so you can heat a 75 sq. ft. zone a long distance from the boiler doesn't sound very efficient.

This past summer we had left thermometers in all the rooms which told us the highest temp and the lowest. There was 2 or 3 days the temps were way too high but the rest of the summer it was right where we'd want it to be. T
We did a test with a portable job site propane heater and cranked it up got the all the rooms to about 100 degrees and to see if we could cool them down if need be. We have a large exhaust fan that once the doors were open to the stairwell and first floor the rooms were all cooled off in less then 10 min.
The issue is heat for the winter it's 41 degrees on the second floor right now, it's 8 degrees outside. The third floor is even colder at 36 degrees but that floor needs to be finished and insulated correctly.

 

[Unregistered Guest]

That's what I was thinking but I've been told conflicting info on running a propane boiler with the pex tubing directly attached to the floor. Was told since the boiler runs at about 160 degrees the wood floor would be very hot and most likely start to warp due to the heat.

Are you doing this install yourself? If you aren't then run away from who told you that. That's what mixing valves are for. It mixes the cool return water with the 160-180 degree boiler water to lower the supply temp down to 100-115.

 

[NCDave]

I'm in NC, so our winters are not as extreme as yours, but there are lots of factors to consider. I'm a residential builder and over the years several clients have requested heated floors in large areas for both animals and automotive hobbies. I've also been a dealer for several years of gas water heating equipment above the level of what you see on the shelves at Lowes or HD. In the earlier years I used a HE power vented tank unit with space heating taps to handle this type of need but in the past decade or so I've leaned toward tankless water heaters for this application. A tankless heater won't replace a boiler system, but your application doesn't sound like it would warrant the cost of a boiler system.

A Gas powered tankless water heating system can work efficiently at lower temps than the boiler (140 is usually the max on a tankless unit), but as they are computer controlled with variable output burners, they are much less costly to operate. And they have several other advantages:
- They can be a diy install in many instances if you have a working knowledge of plumbing.
- They are compact. In fact, they can be mounted outside the building. This is my favorite method. They pretty much all now have anti-freeze technology and with proper installation are not weather sensitive.
- If you do have a failure, you don't have to wait a week on a plumber. With proper installation and care, they have a typical lifespan of 20-25 yrs.
-Mounted in an open loop system, they can also supply domestic hot water.
- They will heat a lot bigger space than you would imagine.

A couple of years ago I broke with my norm and installed an electric tankless unit to heat the floor of a 26 x 32 garage. The heater I used came from Home Depot Online and was a Rheem 60kw 220v unit. I think the heater itself was about $260. That combined with 500' of pex tubing buried in the floor over a radiant barrier, a recirculation pump, isolation valves, a controller and a thermostat was all that was needed for the system. The system supplied both water for the floor and served hot water faucets on the outside of the garage. The first winter of operation (2015) had some pretty cold temps and the owner monitored the garage temps every day (retired guys can do that, I guess). He set the thermostat at 60 and said he only saw it drop once under that and that morning it was 56 after a night in the teens. It was back to 60 by 9 am.

I don't think you can get by with an electric system for your application, but a propane powered tankless water heating system would do the job.

The key on any system's success is DESIGN. Your building would have to be assessed for heat loss (not extremely complicated) in order to determine the system capacity you need. VERY FEW hvac people do this unless it's a building code requirement and the job is permitted. In my 30+ years as a builder and renovation contractor, I have found that small systems, as well as system replacements, most hvac guys don't want to inconvenience the county or city officials with permits and inspections. And most fly by the seat of their pants on system sizing on the non-permit jobs. Their equipment type recommendations appear to have more to do with what they get the best deal on as opposed to what you actually need to do the job. Most residential heating systems are geared towards homes from about 1,000 sf and up, so most anything these guys are going to suggest is going to be oversized for your application.

Just something to think about.